Merge refreshed schema DSL into canonical tool outputs

2026-08-15 21:04:50 +00:00 · 2026-07-22 22:46:10 +08:00
parent 8930a63b18 c51c02cafa
commit 3d9240e423
32 changed files with 1208 additions and 61 deletions
--- a/.agents/notes/implemented/testing/2026-06-19-acp-snapshot-tests.md
+++ b/.agents/notes/implemented/testing/2026-06-19-acp-snapshot-tests.md
@@ -18,6 +18,8 @@ A snapshot test boots the real ACP example, drives its stdio protocol from a det

 Each scenario's `session.jsonl` is harvested from a real run. `assistant/chunk` events reproduce the model streams; tool, message, and boundary events capture the harness behavior. One ordinary session artifact therefore serves as both replay source and behavioral expected output.

+When a scenario pins an alternative physical storage layout, its fixture is mechanically derived from a real unpacked counterpart. The scenario test requires every intended storage-row kind and exact event-for-event equality after decoding before the ordinary replay and log comparison proves that the assembled process consumes and reproduces that layout.
+
 ### Replay derives the model script from the log

 `llm-replay` short-circuits the provider-agnostic `llm/stream` waterfall. `deriveReplayScript()` groups recorded chunks by `(turn, step)` and serves one group per model call. The loop makes one stream call per step, so the grouping is exact and includes error finish chunks without special handling.
--- a/.agents/notes/implemented/testing/2026-07-08-shared-acp-snapshot-package.md
+++ b/.agents/notes/implemented/testing/2026-07-08-shared-acp-snapshot-package.md
@@ -18,7 +18,7 @@ The machinery lives in [`packages/support/acp-snapshot`](../../../../packages/su

 **`src/normalize.ts`** — the pure normalizers, hook-free by policy: when a future event carries a new volatile field (an approval duration, say), the shared normalizer learns it in the same change, keeping one home for what "normalized" means rather than per-suite scrub extensions.

-**`src/suite.ts`** — the `Scenario` type and `defineAcpSnapshotSuite(options)`, registering the per-scenario compares, record/refresh fixture write-back, the header pin with its live uniformity guard, and the fixture guard block (no orphan scenario dirs, required files present, exactly one pin per class, every JSONL a `scrubSystemPrompts` fixed point, non-pinning fixtures also `scrubRequestHeaders` fixed points). A scenario directory's `session.jsonl` plus contiguous `session.<n>.jsonl` siblings are its ordered primary/child inventory, so the scenario table declares policy without duplicating a child count. The pinned-header contract ([pinned-header Agent Note](2026-07-06-pin-request-header-content-in-one-scenario.md)) is per-suite: each header class flags exactly one `pinsHeader` scenario, whose `system-prompt.expected.md` and JSONL tool list split the composed header into reviewable artifacts; the uniformity guard compares both against every live header in that class. A pinning scenario declares any legitimate changed-header count, and its Markdown artifact records every full changed prompt. The pure helpers (`sessionFixtureNames`, `fixtureContext`, `normalizedHeaders`, `normalizedSystemPrompts`, `formatSystemPromptSnapshot`, `headerChangeCount`) are exported from the module for direct unit coverage.
+**`src/suite.ts`** — the `Scenario` type and `defineAcpSnapshotSuite(options)`, registering the per-scenario compares, record/refresh fixture write-back, the header pin with its live uniformity guard, and the fixture guard block (no orphan scenario dirs, required files present, exactly one pin per class, every JSONL a `scrubSystemPrompts` fixed point, non-pinning fixtures also `scrubRequestHeaders` fixed points). Refresh expands packed timing envelopes before aligning existing volatile event times, so switching between packed and unpacked layouts cannot shift later records; fresh chunk-fragment arrays remain authoritative because their boundaries are replay behavior. A scenario directory's `session.jsonl` plus contiguous `session.<n>.jsonl` siblings are its ordered primary/child inventory, so the scenario table declares policy without duplicating a child count. The pinned-header contract ([pinned-header Agent Note](2026-07-06-pin-request-header-content-in-one-scenario.md)) is per-suite: each header class flags exactly one `pinsHeader` scenario, whose `system-prompt.expected.md` and JSONL tool list split the composed header into reviewable artifacts; the uniformity guard compares both against every live header in that class. A pinning scenario declares any legitimate changed-header count, and its Markdown artifact records every full changed prompt. The pure helpers (`sessionFixtureNames`, `fixtureContext`, `normalizedHeaders`, `normalizedSystemPrompts`, `formatSystemPromptSnapshot`, `headerChangeCount`) are exported from the module for direct unit coverage.

 ## Alternatives considered

--- a/docs/config-catalog.md
+++ b/docs/config-catalog.md
@@ -60,6 +60,8 @@ export interface Config {
  sessionTitle?: NonNullable<agentCore.Config['sessionTitle']>
  /** Directory the JSONL session backend writes under. Defaults to `./.sessions`. */
  persistenceRoot?: string
+  /** Write delta-chunk runs as packed storage rows (the JSONL backend's `packChunks`). Defaults to `false`. */
+  packChunks?: boolean
  /** JSONL artifact encoding; defaults to checksummed Zstandard frames. */
  persistenceCompression?: JsonlCompression
  /** Controls automatic AGENTS.md/CLAUDE.md loading; configure a byte budget or set `false`. */
@@ -638,7 +640,7 @@ export interface ReplayModelConfig {
 }
 ```

-Source: [`packages/support/llm-replay/src/index.ts:385`](../packages/support/llm-replay/src/index.ts)
+Source: [`packages/support/llm-replay/src/index.ts:387`](../packages/support/llm-replay/src/index.ts)

 ## `@deepseek-ai/dsh-llm-retry`

@@ -889,7 +891,7 @@ Source: [`packages/sandbox/sandbox-policy/src/index.ts:44`](../packages/sandbox/
 Requires: `sessions`

 ```ts config-catalog
-/** Plugin config: where the JSONL backend keeps its session logs (`root` is required — no default). */
+/** Plugin config: where the JSONL backend keeps its session logs, and the packed-row write switch. */
 export interface Config {
  /**
   * Root directory for all session files. Required (no default): a default of
@@ -897,6 +899,15 @@ export interface Config {
   * (bash calls, subprocesses). Sessions group under per-cwd subdirectories.
   */
  root: string
+  /**
+   * Write runs of consecutive `assistant/chunk` delta events as packed
+   * `text-chunks`/`reasoning-chunks`/`tool-call-chunks` rows (lossless,
+   * ~60% smaller logs measured on a real session). Off by default while
+   * snapshot fixtures stay in the one-event-per-line layout: recording with
+   * packing on rewrites every golden `session.jsonl`. READING packed rows is
+   * unconditional — a log's layout never depends on this switch.
+   */
+  packChunks?: boolean
  /** Physical encoding; defaults to checksummed Zstandard frames. */
  compression?: JsonlCompression
 }
--- a/docs/cordis-catalog/events.md
+++ b/docs/cordis-catalog/events.md
@@ -569,7 +569,7 @@ Creation announcement during session publication. A synchronous throw vetoes and

 Types: [Scoped](../core-data-structures/scope.md) · [Session](../core-data-structures/session.md)

-Source: [`packages/core/session/src/index.ts:68`](../../packages/core/session/src/index.ts)
+Source: [`packages/core/session/src/index.ts:70`](../../packages/core/session/src/index.ts)

 ### `session/disposed` — emit

@@ -590,7 +590,7 @@ Emitted once when an announced session leaves the store, including publication r

 Types: [Scoped](../core-data-structures/scope.md) · [Session](../core-data-structures/session.md)

-Source: [`packages/core/session/src/index.ts:78`](../../packages/core/session/src/index.ts)
+Source: [`packages/core/session/src/index.ts:80`](../../packages/core/session/src/index.ts)

 ### `session/event` — emit

@@ -613,7 +613,7 @@ Post-commit, fire-and-forget append feed. The listener snapshot resolves before

 Types: [Scoped](../core-data-structures/scope.md) · [Session](../core-data-structures/session.md) · [SessionEvent](../core-data-structures/core.md)

-Source: [`packages/core/session/src/index.ts:90`](../../packages/core/session/src/index.ts)
+Source: [`packages/core/session/src/index.ts:92`](../../packages/core/session/src/index.ts)

 ### `session/flush` — parallel

@@ -634,7 +634,7 @@ Awaited parallel durability checkpoint: every listener runs and the caller await

 Types: [Scoped](../core-data-structures/scope.md) · [Session](../core-data-structures/session.md)

-Source: [`packages/core/session/src/index.ts:100`](../../packages/core/session/src/index.ts)
+Source: [`packages/core/session/src/index.ts:102`](../../packages/core/session/src/index.ts)

 ## `subagent/*`

--- a/docs/cordis-catalog/services.md
+++ b/docs/cordis-catalog/services.md
@@ -1059,7 +1059,7 @@ fork(source: SessionForkSource, boundary?: number, childSessionId?: SessionId):

 Types: [CreateSessionOptions](../core-data-structures/persistence.md) · [OutOfBandSessionEventType](../core-data-structures/session.md) · [Session](../core-data-structures/session.md) · [SessionEvent](../core-data-structures/core.md) · [SessionEventMap](../core-data-structures/session.md) · [SessionId](../core-data-structures/core.md) · [TurnTrigger](../core-data-structures/session.md)

-Source: [`packages/core/session/src/index.ts:592`](../../packages/core/session/src/index.ts)
+Source: [`packages/core/session/src/index.ts:594`](../../packages/core/session/src/index.ts)

 ## `ctx.sessionTitle` — `SessionTitleService`

--- a/docs/core-data-structures/session.md
+++ b/docs/core-data-structures/session.md
@@ -538,6 +538,6 @@ The hook bridges' `hook/invoked` / `hook/result` provenance pairs (from `@deepse

 ## Durability contract

-What a persistence backend relies on: the durable log persists every event verbatim, **including** `assistant/chunk` — `seq` must stay contiguous, so chunks cannot be filtered out of the canonical log. All `event.data` must be JSON-serializable; `Session.append` enforces this at the source (throwing on non-serializable data), so a bad event never enters the log and `session.events` always equals what a backend can persist. Adding an event type that carries non-serializable data, or that breaks the turn/step nesting checked by the session invariant companion, is a breaking change to the on-disk format.
+What a persistence backend relies on: the durable log persists every event losslessly, **including** `assistant/chunk` — `seq` must stay contiguous, so chunks cannot be filtered out of the canonical log. A backend may choose its own storage encoding for an event batch as long as `load` returns the exact appended events (the JSONL backend's opt-in packed chunk rows are such an encoding — see [persistence.md](persistence.md)). All `event.data` must be JSON-serializable; `Session.append` enforces this at the source (throwing on non-serializable data), so a bad event never enters the log and `session.events` always equals what a backend can persist. Adding an event type that carries non-serializable data, or that breaks the turn/step nesting checked by the session invariant companion, is a breaking change to the on-disk format.

 The backends that consume this contract are on [persistence.md](persistence.md).
--- a/docs/event-producer-consumer.md
+++ b/docs/event-producer-consumer.md
@@ -31,10 +31,10 @@ This matrix shows which packages dispatch each harness-owned event and which pac
 | `fs/write-intent` | `waterfall` | [`packages/fs/fs/src/index.ts:54`](../packages/fs/fs/src/index.ts) | [`tool-fs`](../packages/fs/tool-fs) (`waterfall`) | [`fs-policy`](../packages/fs/fs-policy) |
 | `goal/changed` | `emit` | [`packages/goal/goal/src/types.ts:167`](../packages/goal/goal/src/types.ts) | [`goal`](../packages/goal/goal) (`emit`) | [`goal-session`](../packages/goal/goal-session) |
 | `llm/stream` | `waterfall` | [`packages/llm/llm/src/index.ts:52`](../packages/llm/llm/src/index.ts) | [`llm`](../packages/llm/llm) (`waterfall`) | [`agent-loop`](../packages/core/agent-loop), [`llm`](../packages/llm/llm), [`llm-replay`](../packages/support/llm-replay), [`session-checkpoint-policy`](../packages/session-persistence/session-checkpoint-policy), [`session-title`](../packages/session-title/session-title) |
-| `session/created` | `emit` | [`packages/core/session/src/index.ts:68`](../packages/core/session/src/index.ts) | [`session`](../packages/core/session) (`events.dispatch`) | [`compact`](../packages/compact/compact), [`goal`](../packages/goal/goal), [`hook-protocol`](../packages/hooks/hook-protocol), [`jsonrpc`](../packages/ui/jsonrpc), [`llm-retry`](../packages/llm/llm-retry), `runtime`, [`session`](../packages/core/session), [`session-persistence`](../packages/session-persistence/session-persistence), [`user-approval`](../packages/ui/user-approval) |
-| `session/disposed` | `emit` | [`packages/core/session/src/index.ts:78`](../packages/core/session/src/index.ts) | [`session`](../packages/core/session) (`events.dispatch`) | [`agent-loop`](../packages/core/agent-loop), `runtime`, [`session-persistence`](../packages/session-persistence/session-persistence), [`session-title`](../packages/session-title/session-title) |
-| `session/event` | `emit` | [`packages/core/session/src/index.ts:90`](../packages/core/session/src/index.ts) | [`session`](../packages/core/session) (`events.dispatch`) | [`acp`](../packages/ui/acp), [`cli-demo`](../packages/examples/cli-demo), [`compact`](../packages/compact/compact), [`goal`](../packages/goal/goal), [`goal-session`](../packages/goal/goal-session), [`hook-protocol`](../packages/hooks/hook-protocol), [`jsonrpc`](../packages/ui/jsonrpc), `runtime`, [`session`](../packages/core/session), [`session-persistence`](../packages/session-persistence/session-persistence), [`session-title`](../packages/session-title/session-title), [`token-meter`](../packages/llm/token-meter), [`tui`](../packages/ui/tui), [`user-approval`](../packages/ui/user-approval), [`workspace-context`](../packages/context/workspace-context) |
-| `session/flush` | `parallel` | [`packages/core/session/src/index.ts:100`](../packages/core/session/src/index.ts) | [`session`](../packages/core/session) (`events.dispatch`) | [`session-persistence`](../packages/session-persistence/session-persistence) |
+| `session/created` | `emit` | [`packages/core/session/src/index.ts:70`](../packages/core/session/src/index.ts) | [`session`](../packages/core/session) (`events.dispatch`) | [`compact`](../packages/compact/compact), [`goal`](../packages/goal/goal), [`hook-protocol`](../packages/hooks/hook-protocol), [`jsonrpc`](../packages/ui/jsonrpc), [`llm-retry`](../packages/llm/llm-retry), `runtime`, [`session`](../packages/core/session), [`session-persistence`](../packages/session-persistence/session-persistence), [`user-approval`](../packages/ui/user-approval) |
+| `session/disposed` | `emit` | [`packages/core/session/src/index.ts:80`](../packages/core/session/src/index.ts) | [`session`](../packages/core/session) (`events.dispatch`) | [`agent-loop`](../packages/core/agent-loop), `runtime`, [`session-persistence`](../packages/session-persistence/session-persistence), [`session-title`](../packages/session-title/session-title) |
+| `session/event` | `emit` | [`packages/core/session/src/index.ts:92`](../packages/core/session/src/index.ts) | [`session`](../packages/core/session) (`events.dispatch`) | [`acp`](../packages/ui/acp), [`cli-demo`](../packages/examples/cli-demo), [`compact`](../packages/compact/compact), [`goal`](../packages/goal/goal), [`goal-session`](../packages/goal/goal-session), [`hook-protocol`](../packages/hooks/hook-protocol), [`jsonrpc`](../packages/ui/jsonrpc), `runtime`, [`session`](../packages/core/session), [`session-persistence`](../packages/session-persistence/session-persistence), [`session-title`](../packages/session-title/session-title), [`token-meter`](../packages/llm/token-meter), [`tui`](../packages/ui/tui), [`user-approval`](../packages/ui/user-approval), [`workspace-context`](../packages/context/workspace-context) |
+| `session/flush` | `parallel` | [`packages/core/session/src/index.ts:102`](../packages/core/session/src/index.ts) | [`session`](../packages/core/session) (`events.dispatch`) | [`session-persistence`](../packages/session-persistence/session-persistence) |
 | `subagent/end` | `emit` | [`packages/subagent/subagent/src/index.ts:139`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`events.dispatch`) | [`hooks-claude`](../packages/hooks/hooks-claude), [`jsonrpc`](../packages/ui/jsonrpc), [`subagent`](../packages/subagent/subagent) |
 | `subagent/provider-added` | `emit` | [`packages/subagent/subagent/src/index.ts:113`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`emit`) | [`subagent`](../packages/subagent/subagent), [`tool-subagent`](../packages/subagent/tool-subagent) |
 | `subagent/provider-removed` | `emit` | [`packages/subagent/subagent/src/index.ts:119`](../packages/subagent/subagent/src/index.ts) | [`subagent`](../packages/subagent/subagent) (`events.dispatch`) | [`subagent`](../packages/subagent/subagent), [`tool-subagent`](../packages/subagent/tool-subagent) |
--- a/examples/acp-agent/packed-chunks.cordis.snapshot.yml
+++ b/examples/acp-agent/packed-chunks.cordis.snapshot.yml
@@ -0,0 +1,45 @@
+# Keyless replay counterpart of packed-chunks.cordis.yml. Patches do not
+# compose across includes, so this applies the packChunks config and the
+# DeepSeek-to-replay swap directly to `cordis.yml`.
+- id: base
+  name: '@cordisjs/plugin-include'
+  config:
+    path: ./cordis.yml
+    patches:
+      - id: llm-deepseek
+        name: '@deepseek-ai/dsh-llm-deepseek'
+        disabled: true
+      - id: sandbox
+        name: '@deepseek-ai/dsh-sandbox-local'
+        config:
+          runnerCommand:
+            - bash
+            - -c
+            - while [ "$1" != "--" ]; do shift; done; shift; exec "$@"
+            - passthrough-runner
+          runnerFailureSignatures:
+            - 'passthrough-runner: profile rejected'
+      - id: acp-agent
+        name: '@deepseek-ai/dsh-acp-demo'
+        config:
+          provider: deepseek
+          model: deepseek-v4-flash
+          persistenceRoot: !!js process.env.DSH_SNAPSHOT_SESSIONS_ROOT ?? './.sessions'
+          persistenceCompression: 'none'
+          packChunks: true
+          workspaceContext:
+            maxBytes: 65536
+          persona: |
+            You are a coding assistant powered by the {{model}} model. Your working directory is {{cwd}}. Your bash tool runs under a file sandbox — a `[sandbox: file access denied …]` result is policy, not a command bug.
+
+            Verify your work by running the code or tests. Keep answers brief and factual.
+      - insert:
+          - id: llm-replay
+            name: '@deepseek-ai/dsh-llm-replay'
+            config:
+              providers:
+                - id: deepseek
+                  name: DeepSeek
+                  models:
+                    - id: deepseek-v4-flash
+                    - id: deepseek-v4-pro
--- a/examples/acp-agent/packed-chunks.cordis.yml
+++ b/examples/acp-agent/packed-chunks.cordis.yml
@@ -0,0 +1,23 @@
+# The packed-chunk-rows overlay: the base tree with the JSONL backend's
+# `packChunks` switched on, so delta-chunk runs persist as packed storage rows.
+# A config patch replaces the whole app config, so unchanged base fields are
+# restated below.
+- id: base
+  name: '@cordisjs/plugin-include'
+  config:
+    path: ./cordis.yml
+    patches:
+      - id: acp-agent
+        name: '@deepseek-ai/dsh-acp-demo'
+        config:
+          provider: deepseek
+          model: deepseek-v4-flash
+          persistenceRoot: !!js process.env.DSH_SNAPSHOT_SESSIONS_ROOT ?? './.sessions'
+          persistenceCompression: !!js "process.env.DSH_SNAPSHOT === undefined ? 'zstd' : 'none'"
+          packChunks: true
+          workspaceContext:
+            maxBytes: 65536
+          persona: |
+            You are a coding assistant powered by the {{model}} model. Your working directory is {{cwd}}. Your bash tool runs under a file sandbox — a `[sandbox: file access denied …]` result is policy, not a command bug.
+
+            Verify your work by running the code or tests. Keep answers brief and factual.
--- a/examples/acp-agent/tests/acp.snapshot.ts
+++ b/examples/acp-agent/tests/acp.snapshot.ts
@@ -1,7 +1,10 @@
 import { fileURLToPath } from 'node:url'
+import { readFileSync } from 'node:fs'
 import { dirname, join } from 'node:path'
 import { homedir } from 'node:os'
+import { expect, it } from 'vitest'
 import { defineAcpSnapshotSuite, type Scenario, type SnapshotSuiteOptions } from '@deepseek-ai/dsh-acp-snapshot'
+import { decodeStorageRecord } from '@deepseek-ai/dsh-session'

 /**
 * The acp-agent example's snapshot suite: the scenario table for
@@ -32,8 +35,18 @@ const WORKSPACE_CONTEXT_CONFIG = fileURLToPath(new URL('../workspace-context.cor
 const ADVANCED_CONFIG = fileURLToPath(new URL('../advanced.cordis.yml', import.meta.url))
 const FS_CONFIG = fileURLToPath(new URL('../fs.cordis.yml', import.meta.url))
 const DEPTH_TWO_CONFIG = fileURLToPath(new URL('../depth-two.cordis.yml', import.meta.url))
+const PACKED_CHUNKS_CONFIG = fileURLToPath(new URL('../packed-chunks.cordis.yml', import.meta.url))
 const SESSION_SANDBOX_ROOT_CONFIG = fileURLToPath(new URL('../session-sandbox-root.cordis.yml', import.meta.url))
 const LSP_CONFIG = fileURLToPath(new URL('./lsp.cordis.yml', import.meta.url))
+const SNAPSHOTS_DIR = join(dirname(fileURLToPath(import.meta.url)), 'snapshots')
+const PACKED_CHUNKS_SOURCE = 'hook-cc-pretool-deny'
+
+function fixtureRecords(name: string): unknown[] {
+  return readFileSync(join(SNAPSHOTS_DIR, name, 'session.jsonl'), 'utf8')
+    .trimEnd()
+    .split('\n')
+    .map(line => JSON.parse(line) as unknown)
+}

 function snapshotModeFromEnv(value: string | undefined): SnapshotSuiteOptions['mode'] {
  switch (value) {
@@ -73,6 +86,10 @@ const SCENARIOS: Scenario[] = [
  // Its prompt and tool-schema sidecars pin the composed header.
  { name: 'text-turn', hasModelTurn: true, recorded: true, pinsHeader: true },
  { name: 'tool-call-turn', hasModelTurn: true, recorded: true },
+  // Authored from the real PACKED_CHUNKS_SOURCE recording under the same app
+  // composition. The contract below pins decoded equality and all three row
+  // kinds; replay additionally proves the assembled app re-packs identically.
+  { name: 'packed-chunks', hasModelTurn: true, recorded: false, configPath: PACKED_CHUNKS_CONFIG },
  // The fs overlay only adds the spill stack (the sandboxed filesystem tools
  // live in the base tree), so these scenarios share the default header class.
  {
@@ -232,7 +249,20 @@ const SCENARIOS: Scenario[] = [

 defineAcpSnapshotSuite({
  agent: AGENT,
-  snapshotsDir: join(dirname(fileURLToPath(import.meta.url)), 'snapshots'),
+  snapshotsDir: SNAPSHOTS_DIR,
  scenarios: SCENARIOS,
  mode: snapshotModeFromEnv(process.env.DSH_SNAPSHOT),
 })
+
+it('packed ACP fixture retains every chunk row kind without changing the logical session', () => {
+  const source = fixtureRecords(PACKED_CHUNKS_SOURCE)
+  const packed = fixtureRecords('packed-chunks')
+  const rowTypes = packed.flatMap((record) => {
+    if (record === null || typeof record !== 'object') return []
+    const type = (record as { type?: unknown }).type
+    return type === 'text-chunks' || type === 'reasoning-chunks' || type === 'tool-call-chunks' ? [type] : []
+  })
+
+  expect([...new Set(rowTypes)].sort()).toStrictEqual(['reasoning-chunks', 'text-chunks', 'tool-call-chunks'])
+  expect([packed[0], ...packed.slice(1).flatMap(record => decodeStorageRecord(record))]).toStrictEqual(source)
+})
--- a/examples/acp-agent/tests/snapshots/packed-chunks/input.json
+++ b/examples/acp-agent/tests/snapshots/packed-chunks/input.json
@@ -0,0 +1,7 @@
+{
+  "steps": [
+    { "op": "initialize" },
+    { "op": "newSession" },
+    { "op": "prompt", "text": "Use the bash tool to run exactly: echo HELLO. Report the tool result you got back verbatim, then stop." }
+  ]
+}
--- a/examples/acp-agent/tests/snapshots/packed-chunks/session.jsonl
+++ b/examples/acp-agent/tests/snapshots/packed-chunks/session.jsonl
@@ -0,0 +1,32 @@
+{"type":"session","version":0,"id":"ff1c1e99-3bd4-4ef8-a954-80d607d628ba","createdAt":1783352165190,"cwd":"/tmp/acp-snap-cwd-wDnkVo","delegationDepth":0}
+{"type":"turn/start","seq":0,"time":1783352165195,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
+{"type":"user/message","seq":1,"time":1783352165196,"data":{"content":[{"type":"text","text":"Use the bash tool to run exactly: echo HELLO. Report the tool result you got back verbatim, then stop."}],"source":{"kind":"user"}},"surfaceOp":"append"}
+{"type":"session/title","seq":2,"time":1783352165196,"data":{"title":"Use the bash tool to","messageSeqs":[1],"source":{"kind":"fallback"}}}
+{"type":"step/start","seq":3,"time":1783352165198,"data":{"turn":1,"step":1}}
+{"type":"request/header","seq":4,"time":1783352165199,"data":{"header":{"config":{"provider":"deepseek","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
+{"type":"assistant/chunk","seq":5,"time":1783352165899,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":0,"blockType":"reasoning"}}}
+{"type":"reasoning-chunks","seq0":6,"time0":1783352165899,"data":{"turn":1,"step":1,"index":0,"dt":[149,27,0,0,1,0,0,28,0,1,0,0,28,0,27,0],"texts":["The"," user"," wants"," me"," to"," run"," a"," simple"," bash"," command"," and"," report"," the"," result"," verb","atim","."]}}
+{"type":"assistant/chunk","seq":23,"time":1783352166218,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":1,"blockType":"tool-call"}}}
+{"type":"tool-call-chunks","seq0":24,"time0":1783352166218,"data":{"turn":1,"step":1,"index":1,"dt":[32,0,0,28,1,0,0,29,0,1,0,27,1,28,0,0,0,29,0,28,0,0,0,31],"id":"call_00_JliP571Bh0QQ8QExbSPk0080","name":"bash","args":["","{","\"","command","\"",": ","\"","echo"," HE","LL","O","\"",", ","\"","description","\"",": ","\"","Run"," echo"," HE","LL","O","\"","}"]}}
+{"type":"assistant/chunk","seq":49,"time":1783352166512,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"reasoning","text":"The user wants me to run a simple bash command and report the result verbatim."}}}}
+{"type":"assistant/chunk","seq":50,"time":1783352166512,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":1,"block":{"type":"tool-call","id":"call_00_JliP571Bh0QQ8QExbSPk0080","name":"bash","arguments":"{\"command\": \"echo HELLO\", \"description\": \"Run echo HELLO\"}"}}}}
+{"type":"assistant/chunk","seq":51,"time":1783352166512,"data":{"turn":1,"step":1,"chunk":{"type":"usage","usage":{"inputTokens":2878,"outputTokens":83,"cacheReadTokens":0,"reasoningTokens":17}}}}
+{"type":"assistant/chunk","seq":52,"time":1783352166512,"data":{"turn":1,"step":1,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}}
+{"type":"assistant/message","seq":53,"time":1783352166514,"data":{"turn":1,"step":1,"content":[{"type":"reasoning","text":"The user wants me to run a simple bash command and report the result verbatim."},{"type":"tool-call","id":"call_00_JliP571Bh0QQ8QExbSPk0080","name":"bash","arguments":"{\"command\": \"echo HELLO\", \"description\": \"Run echo HELLO\"}"}],"provenance":{"provider":"deepseek","model":"deepseek-v4-flash"},"usage":{"inputTokens":2878,"outputTokens":83,"cacheReadTokens":0,"reasoningTokens":17}},"sourceEventSeqs":[5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52],"surfaceOp":"append"}
+{"type":"tool/call","seq":54,"time":1783352166514,"data":{"turn":1,"step":1,"callId":"call_00_JliP571Bh0QQ8QExbSPk0080","name":"bash","arguments":"{\"command\": \"echo HELLO\", \"description\": \"Run echo HELLO\"}"}}
+{"type":"hook/invoked","seq":55,"time":1783352166515,"data":{"turn":1,"point":"PreToolUse","dialect":"claude","handlerId":"claude:PreToolUse:1","matcher":"bash"}}
+{"type":"hook/result","seq":56,"time":1783352166528,"data":{"turn":1,"point":"PreToolUse","handlerId":"claude:PreToolUse:1","decision":"block","exitCode":2,"stderrSummary":"bash is disabled by policy in this session","durationMs":12.367074000000684}}
+{"type":"tool/result","seq":57,"time":1783352166528,"data":{"turn":1,"step":1,"callId":"call_00_JliP571Bh0QQ8QExbSPk0080","content":[{"type":"text","text":"Error: bash is disabled by policy in this session"}],"isError":true},"sourceEventSeqs":[54],"surfaceOp":"append"}
+{"type":"step/end","seq":58,"time":1783352166529,"data":{"turn":1,"step":1}}
+{"type":"step/start","seq":59,"time":1783352166529,"data":{"turn":1,"step":2}}
+{"type":"assistant/chunk","seq":60,"time":1783352167307,"data":{"turn":1,"step":2,"chunk":{"type":"block-start","index":0,"blockType":"reasoning"}}}
+{"type":"reasoning-chunks","seq0":61,"time0":1783352167308,"data":{"turn":1,"step":2,"index":0,"dt":[132,29,0,0,0,0,1,27,0,28,1,0,31,0,25,0,29,1,1,0],"texts":["The"," bash"," tool"," is"," disabled"," by"," policy","."," I"," need"," to"," report"," this"," error"," verb","atim"," back"," to"," the"," user","."]}}
+{"type":"assistant/chunk","seq":82,"time":1783352167613,"data":{"turn":1,"step":2,"chunk":{"type":"block-start","index":1,"blockType":"text"}}}
+{"type":"text-chunks","seq0":83,"time0":1783352167613,"data":{"turn":1,"step":2,"index":1,"dt":[30,29,29,0,1,28,0,1,0,0,0,26,1,0,0,0,28,0,31,0,25,30,1,0,27,1,0,31,1],"texts":["The"," tool"," returned",":\n\n",">"," Error",":"," bash"," is"," disabled"," by"," policy"," in"," this"," session","\n\n","I"," cannot"," run"," the"," command"," because"," the"," bash"," tool"," is"," disabled"," by"," policy","."]}}
+{"type":"assistant/chunk","seq":113,"time":1783352167933,"data":{"turn":1,"step":2,"chunk":{"type":"block-end","index":0,"block":{"type":"reasoning","text":"The bash tool is disabled by policy. I need to report this error verbatim back to the user."}}}}
+{"type":"assistant/chunk","seq":114,"time":1783352167933,"data":{"turn":1,"step":2,"chunk":{"type":"block-end","index":1,"block":{"type":"text","text":"The tool returned:\n\n> Error: bash is disabled by policy in this session\n\nI cannot run the command because the bash tool is disabled by policy."}}}}
+{"type":"assistant/chunk","seq":115,"time":1783352167933,"data":{"turn":1,"step":2,"chunk":{"type":"usage","usage":{"inputTokens":167,"outputTokens":52,"cacheReadTokens":2816,"reasoningTokens":21}}}}
+{"type":"assistant/chunk","seq":116,"time":1783352167933,"data":{"turn":1,"step":2,"chunk":{"type":"finish","reason":{"kind":"stop"}}}}
+{"type":"assistant/message","seq":117,"time":1783352167934,"data":{"turn":1,"step":2,"content":[{"type":"reasoning","text":"The bash tool is disabled by policy. I need to report this error verbatim back to the user."},{"type":"text","text":"The tool returned:\n\n> Error: bash is disabled by policy in this session\n\nI cannot run the command because the bash tool is disabled by policy."}],"provenance":{"provider":"deepseek","model":"deepseek-v4-flash"},"usage":{"inputTokens":167,"outputTokens":52,"cacheReadTokens":2816,"reasoningTokens":21}},"sourceEventSeqs":[60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116],"surfaceOp":"append"}
+{"type":"step/end","seq":118,"time":1783352167934,"data":{"turn":1,"step":2}}
+{"type":"turn/end","seq":119,"time":1783352167934,"data":{"turn":1,"reason":{"kind":"completed"}}}
--- a/examples/acp-agent/tests/snapshots/packed-chunks/stdout.expected.jsonl
+++ b/examples/acp-agent/tests/snapshots/packed-chunks/stdout.expected.jsonl
@@ -0,0 +1,75 @@
+{"jsonrpc":"2.0","id":1,"result":{"protocolVersion":1,"agentInfo":{"name":"deepseek-harness-acp","version":"0.0.1"},"agentCapabilities":{"loadSession":true,"promptCapabilities":{"image":false,"audio":false,"embeddedContext":false}},"authMethods":[]}}
+{"jsonrpc":"2.0","id":2,"result":{"sessionId":"{{sessionId}}","modes":{"availableModes":[{"id":"default","name":"default"},{"id":"plan","name":"plan"}],"currentModeId":"default"},"configOptions":[{"id":"model","name":"Model","description":"Sets this session's provider and model.","category":"model","type":"select","currentValue":"[\"deepseek\",\"deepseek-v4-flash\"]","options":[{"value":"[\"deepseek\",\"deepseek-v4-flash\"]","name":"deepseek-v4-flash"},{"value":"[\"deepseek\",\"deepseek-v4-pro\"]","name":"deepseek-v4-pro"}]},{"id":"permission","name":"Permissions","description":"The session permission preset: each choice bundles a sandbox mode and an approval policy.","category":"mode","type":"select","currentValue":"danger-full-access","options":[{"value":"workspace-write","name":"workspace-write","description":"Write inside the workspace and permitted temporary directories; wider retries require approval."},{"value":"danger-full-access","name":"danger-full-access","description":"Full file access without approval prompts."}]}]}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"available_commands_update","availableCommands":[{"name":"goal","description":"set or view the goal for a long-running task","input":{"hint":"[<objective>|clear|edit <objective>|pause|resume]"}},{"name":"plan","description":"Enter plan mode","input":{"hint":"[message]"}}]}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"session_info_update","title":"Use the bash tool to","updatedAt":"{{updatedAt}}"}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":"The"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" user"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" wants"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" me"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" to"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" run"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" a"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" simple"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" bash"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" command"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" and"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" report"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" the"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" result"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" verb"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":"atim"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":"."}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"tool_call","toolCallId":"call_00_JliP571Bh0QQ8QExbSPk0080","title":"echo HELLO","kind":"execute","status":"in_progress","rawInput":"echo HELLO","content":[{"type":"content","content":{"type":"text","text":"Run echo HELLO"}}]}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"tool_call_update","toolCallId":"call_00_JliP571Bh0QQ8QExbSPk0080","status":"failed","content":[{"type":"content","content":{"type":"text","text":"```console\nError: bash is disabled by policy in this session\n```"}}]}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":"The"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" bash"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" tool"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" is"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" disabled"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" by"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" policy"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":"."}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" I"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" need"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" to"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" report"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" this"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" error"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" verb"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":"atim"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" back"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" to"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" the"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":" user"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_thought_chunk","content":{"type":"text","text":"."}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":"The"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" tool"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" returned"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":":\n\n"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":">"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" Error"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":":"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" bash"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" is"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" disabled"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" by"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" policy"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" in"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" this"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" session"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":"\n\n"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":"I"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" cannot"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" run"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" the"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" command"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" because"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" the"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" bash"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" tool"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" is"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" disabled"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" by"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":" policy"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":"."}}}}
+{"jsonrpc":"2.0","id":3,"result":{"stopReason":"end_turn"}}
--- a/examples/acp-agent/tests/snapshots/packed-chunks/workspace/hooks.json
+++ b/examples/acp-agent/tests/snapshots/packed-chunks/workspace/hooks.json
@@ -0,0 +1,12 @@
+{
+  "hooks": {
+    "PreToolUse": [
+      {
+        "matcher": "bash",
+        "hooks": [
+          { "type": "command", "command": "echo 'bash is disabled by policy in this session' >&2; exit 2" }
+        ]
+      }
+    ]
+  }
+}
--- a/packages/core/session/README.md
+++ b/packages/core/session/README.md
@@ -48,6 +48,10 @@ Plain class (not a Cordis Service). Create via `ctx.sessions.create()`.

 Durable values need one accepted representation, not a check followed by a second read. `isJsonValue(value)` is the boolean predicate; `snapshotJsonValue(value)` iteratively validates and copies a plain value in one pass, returning `undefined` for invalid input and propagating a throwing getter. The snapshot helper accepts finite JSON numbers except `-0` (JSON rewrites it to `0`), dense ordinary arrays, and plain or null-prototype objects; it rejects cycles, unsupported scalars, and exotic prototypes before normalization without imposing a call-stack depth limit.

+### Chunk-row storage codec (`chunk-rows.ts`)
+
+Providers stream token-sized deltas, so a raw log stores hundreds of `assistant/chunk` lines whose JSON envelopes dwarf their payloads. `packChunkRuns(events)` packs each run of ≥3 consecutive same-block delta chunks into one storage row — `text-chunks`, `reasoning-chunks`, or `tool-call-chunks` (bare slash-less tags: storage vocabulary, not `SessionEventMap` members) — and `decodeStorageRecord(value)` expands a parsed line back into its exact events (`seq0`/`time0` + per-member `dt` gaps reconstruct every `seq`/`time`). The encoder whitelists exact shapes and stores anything unrecognized verbatim; the decoder validates row-tagged values and throws on malformation. Owned here so the JSONL backend and the fixture readers (`dsh-llm-replay`, `dsh-acp-snapshot`) share one codec; the write-side switch is the backend's `packChunks` config.
+
 ### Surface types

 - `SurfaceOp` — how an event entered the ordered surface: `'append'` (normal tail append) or `{ op: 'replace', start, end }` (replace entries from `start` through `end` inclusive — both must be valid surface seqs; `start === end` replaces one entry). Used by compaction to shadow old events without deleting them.
--- a/packages/core/session/src/chunk-rows.ts
+++ b/packages/core/session/src/chunk-rows.ts
@@ -0,0 +1,347 @@
+/**
+ * Lossless storage packing for `assistant/chunk` delta runs. Providers stream
+ * token-sized deltas, so a log stores hundreds of near-identical event lines
+ * whose JSON envelopes dwarf their payloads (~56× measured on a real DeepSeek
+ * session). This module packs each run of consecutive same-block delta chunks
+ * into ONE storage row — `text-chunks`, `reasoning-chunks`, or
+ * `tool-call-chunks` — and expands rows back to the exact original events.
+ *
+ * Storage rows are a durable-encoding vocabulary, NOT session events: they
+ * never enter `Session.events`, have no `SessionEventMap` entry, and use bare
+ * (slash-less) type tags so a reader cannot confuse them with the event
+ * taxonomy (precedent: the JSONL header line's `session` tag). The encoder
+ * whitelists exact shapes — anything it does not fully recognize is stored
+ * verbatim, so unknown fields or future chunk variants lose compression, never
+ * data. The decoder validates before expanding and fails loud on a malformed
+ * row-tagged value instead of silently dropping a whole run.
+ *
+ * @module @deepseek-ai/dsh-session/chunk-rows
+ */
+
+import { CallId, assertNever } from '@deepseek-ai/dsh-llm'
+import type { StreamChunk } from '@deepseek-ai/dsh-llm'
+import type { SessionEvent } from './types.ts'
+
+/** The chunk kinds that may pack; block boundaries, usage, and finish chunks always stay one event per line. */
+type DeltaKind = 'text-delta' | 'reasoning-delta' | 'tool-call-delta'
+
+/** A run member: an `assistant/chunk` event whose exact shape the encoder whitelisted. */
+type DeltaEvent = SessionEvent<'assistant/chunk'>
+
+/**
+ * Fields shared by every packed run: placement, block correlation, and member
+ * timestamps as gaps. Member `k` reconstructs as seq `seq0 + k` and time
+ * `time0` plus the first `k` gaps; a gap may be negative when the wall clock
+ * stepped backwards between events.
+ */
+interface RunDataBase {
+  turn: number
+  step: number
+  /** The stream block index every member shares. */
+  index: number
+  /** Epoch-ms gaps between consecutive members; length is one less than the member count. */
+  dt: number[]
+}
+
+/** Payload of a `text-chunks`/`reasoning-chunks` row: one entry per member, never joined — token boundaries are data. */
+interface TextRunData extends RunDataBase {
+  texts: string[]
+}
+
+/** Payload of a `tool-call-chunks` row: the run-constant call identity plus each member's raw arguments fragment. */
+interface ToolCallRunData extends RunDataBase {
+  id: CallId
+  /** Present iff every member carried it, with one uniform value (a mixed run never packs). */
+  name?: string
+  args: string[]
+}
+
+/**
+ * A packed run of consecutive delta chunk events, discriminated on `type`.
+ * `seq0`/`time0` anchor the first member; text and reasoning rows share the
+ * {@link TextRunData} payload, tool-call rows carry {@link ToolCallRunData}.
+ */
+export type ChunkRow =
+  | { type: 'text-chunks'; seq0: number; time0: number; data: TextRunData }
+  | { type: 'reasoning-chunks'; seq0: number; time0: number; data: TextRunData }
+  | { type: 'tool-call-chunks'; seq0: number; time0: number; data: ToolCallRunData }
+
+/** One durable log line's JSON value: a session event verbatim, or a packed chunk row. */
+export type StorageRecord = SessionEvent | ChunkRow
+
+/**
+ * Minimum members before a run packs. Below it a row's envelope rivals the
+ * event lines it replaces. A format constant, not a tunable: both layouts
+ * decode identically, so changing it never invalidates stored logs.
+ */
+const MIN_RUN = 3
+
+function isRecord(value: unknown): value is Record<string, unknown> {
+  return typeof value === 'object' && value !== null
+}
+
+/** Exact-key check: `value` has every key in `keys` and nothing else. */
+function hasExactKeys(value: object, keys: readonly string[]): boolean {
+  return Object.keys(value).length === keys.length && keys.every(k => Object.hasOwn(value, k))
+}
+
+/**
+ * Classify an event for packing: its delta kind when the ENTIRE shape
+ * (envelope, data, chunk — exact keys, primitive types, integer seq/time) is
+ * whitelisted, else `undefined` (store verbatim). Inputs come from live typed
+ * appends AND parsed fixture files, so the checks are structural, not
+ * type-trusted. Integer times keep gap encoding exact: a fractional time would
+ * reconstruct through float subtraction/addition, which need not round-trip.
+ */
+function classify(event: SessionEvent): DeltaKind | undefined {
+  if (event.type !== 'assistant/chunk') return undefined
+  if (!hasExactKeys(event, ['type', 'seq', 'time', 'data'])) return undefined
+  if (!Number.isSafeInteger(event.seq) || event.seq < 0 || !Number.isSafeInteger(event.time)) return undefined
+  const data: unknown = event.data
+  if (!isRecord(data) || !hasExactKeys(data, ['turn', 'step', 'chunk'])) return undefined
+  if (typeof data.turn !== 'number' || typeof data.step !== 'number') return undefined
+  const chunk = data.chunk
+  if (!isRecord(chunk) || typeof chunk.index !== 'number') return undefined
+  switch (chunk.type) {
+    case 'text-delta':
+    case 'reasoning-delta':
+      return hasExactKeys(chunk, ['type', 'index', 'text']) && typeof chunk.text === 'string'
+        ? chunk.type
+        : undefined
+    case 'tool-call-delta': {
+      const shapeOk = hasExactKeys(chunk, ['type', 'index', 'id', 'argumentsDelta'])
+        || (hasExactKeys(chunk, ['type', 'index', 'id', 'name', 'argumentsDelta']) && typeof chunk.name === 'string')
+      return shapeOk && typeof chunk.id === 'string' && typeof chunk.argumentsDelta === 'string'
+        ? chunk.type
+        : undefined
+    }
+    // Whitelist fall-through over parsed data: block-start/end, usage, finish,
+    // and any future chunk variant stay one event per line.
+    default:
+      return undefined
+  }
+}
+
+/** The tool-call fields of a whitelisted delta chunk (only after {@link classify} returned `'tool-call-delta'`). */
+function toolCallOf(event: DeltaEvent): { id: string; name?: string } {
+  return event.data.chunk as { id: string; name?: string }
+}
+
+/** The block index of a whitelisted delta chunk (not every {@link StreamChunk} variant carries one). */
+function indexOf(event: DeltaEvent): number {
+  return (event.data.chunk as { index: number }).index
+}
+
+/** Whether `next` extends a run ending in `prev` (same kind already checked by the caller). */
+function continues(prev: DeltaEvent, next: DeltaEvent, kind: DeltaKind): boolean {
+  if (next.seq !== prev.seq + 1) return false
+  // Two safe-integer times can sit further apart than a double subtracts
+  // exactly (2^53-1 and its negation differ by ~2^54); a rounded gap would
+  // decode to a different timestamp. The check is exact in both directions: a
+  // true gap within safe range subtracts without rounding and passes, while a
+  // true gap beyond it rounds to a value that is itself beyond and fails.
+  if (!Number.isSafeInteger(next.time - prev.time)) return false
+  if (next.data.turn !== prev.data.turn || next.data.step !== prev.data.step) return false
+  if (indexOf(next) !== indexOf(prev)) return false
+  if (kind !== 'tool-call-delta') return true
+  const a = toolCallOf(prev)
+  const b = toolCallOf(next)
+  // `name` must match in presence AND value — a mixed run is not representable.
+  return a.id === b.id && Object.hasOwn(a, 'name') === Object.hasOwn(b, 'name') && a.name === b.name
+}
+
+/** Build the row for a completed run (`run.length >= MIN_RUN`, uniform per {@link continues}). */
+function buildRow(kind: DeltaKind, run: readonly DeltaEvent[]): ChunkRow {
+  const first = run[0] as DeltaEvent
+  const base = {
+    turn: first.data.turn,
+    step: first.data.step,
+    index: indexOf(first),
+    dt: run.slice(1).map((event, i) => event.time - (run[i] as DeltaEvent).time),
+  }
+  const envelope = { seq0: first.seq, time0: first.time }
+  if (kind === 'tool-call-delta') {
+    const call = toolCallOf(first)
+    return {
+      type: 'tool-call-chunks',
+      ...envelope,
+      data: {
+        ...base,
+        id: CallId(call.id),
+        ...Object.hasOwn(call, 'name') ? { name: call.name as string } : {},
+        args: run.map(event => (event.data.chunk as { argumentsDelta: string }).argumentsDelta),
+      },
+    }
+  }
+  const data = { ...base, texts: run.map(event => (event.data.chunk as { text: string }).text) }
+  return kind === 'text-delta'
+    ? { type: 'text-chunks', ...envelope, data }
+    : { type: 'reasoning-chunks', ...envelope, data }
+}
+
+/**
+ * Pack an event batch for storage: each run of at least {@link MIN_RUN}
+ * consecutive whitelisted same-kind, same-block delta chunk events becomes one
+ * {@link ChunkRow}; every other event passes through verbatim, in order.
+ * Pure and stateless — safe over any array, including a batch whose runs were
+ * split by flush boundaries (the split runs simply pack per batch).
+ *
+ * @param events - the batch to encode, in log order.
+ * @returns the storage records to write, one JSONL line each.
+ */
+export function packChunkRuns(events: readonly SessionEvent[]): StorageRecord[] {
+  const out: StorageRecord[] = []
+  let kind: DeltaKind | undefined
+  let run: DeltaEvent[] = []
+  const flush = (): void => {
+    if (kind !== undefined && run.length >= MIN_RUN) out.push(buildRow(kind, run))
+    else out.push(...run)
+    kind = undefined
+    run = []
+  }
+  for (const event of events) {
+    const k = classify(event)
+    if (k === undefined) {
+      flush()
+      out.push(event)
+      continue
+    }
+    const delta = event as DeltaEvent
+    const last = run[run.length - 1]
+    if (k === kind && last !== undefined && continues(last, delta, k)) {
+      run.push(delta)
+      continue
+    }
+    flush()
+    kind = k
+    run = [delta]
+  }
+  flush()
+  return out
+}
+
+/** Throw the uniform malformed-row diagnostic. */
+function malformed(tag: string, why: string): never {
+  throw new Error(`malformed ${tag} storage row: ${why}`)
+}
+
+/** Validate the shared run-data fields and the payload/dt arity; returns the member payload. */
+function validateRunData(tag: string, data: Record<string, unknown>, payloadKey: 'texts' | 'args'): string[] {
+  if (typeof data.turn !== 'number' || typeof data.step !== 'number' || typeof data.index !== 'number') {
+    malformed(tag, 'turn/step/index must be numbers')
+  }
+  const payload = data[payloadKey]
+  if (!Array.isArray(payload) || payload.length === 0 || payload.some(entry => typeof entry !== 'string')) {
+    malformed(tag, `${payloadKey} must be a non-empty string array`)
+  }
+  const dt = data.dt
+  if (!Array.isArray(dt) || dt.some(gap => !Number.isSafeInteger(gap))) {
+    malformed(tag, 'dt must be an array of safe integers')
+  }
+  if (dt.length !== payload.length - 1) {
+    malformed(tag, `dt length ${dt.length} does not match ${payload.length} members`)
+  }
+  return payload as string[]
+}
+
+/** Validate a row-tagged parsed value's envelope and data, throwing on any malformation. */
+function validateRow(value: Record<string, unknown>, tag: ChunkRow['type']): ChunkRow {
+  if (!hasExactKeys(value, ['type', 'seq0', 'time0', 'data'])) {
+    malformed(tag, 'envelope must be exactly {type, seq0, time0, data}')
+  }
+  if (!Number.isSafeInteger(value.seq0) || (value.seq0 as number) < 0) {
+    malformed(tag, 'seq0 must be a non-negative safe integer')
+  }
+  if (!Number.isSafeInteger(value.time0)) {
+    malformed(tag, 'time0 must be a safe integer')
+  }
+  const data = value.data
+  if (!isRecord(data)) malformed(tag, 'data must be an object')
+  let payload: string[]
+  if (tag === 'tool-call-chunks') {
+    const withName = hasExactKeys(data, ['turn', 'step', 'index', 'id', 'name', 'dt', 'args'])
+    if (!withName && !hasExactKeys(data, ['turn', 'step', 'index', 'id', 'dt', 'args'])) {
+      malformed(tag, 'data must be exactly {turn, step, index, id, name?, dt, args}')
+    }
+    if (typeof data.id !== 'string' || (withName && typeof data.name !== 'string')) {
+      malformed(tag, 'id (and name when present) must be strings')
+    }
+    payload = validateRunData(tag, data, 'args')
+  } else {
+    if (!hasExactKeys(data, ['turn', 'step', 'index', 'dt', 'texts'])) {
+      malformed(tag, 'data must be exactly {turn, step, index, dt, texts}')
+    }
+    payload = validateRunData(tag, data, 'texts')
+  }
+  // Reconstruction bounds. The encoder only packs runs whose member seqs and
+  // times are all safe integers, so a running value that leaves safe range is
+  // outside any encoder's image: float arithmetic would round it to a
+  // different number than exact arithmetic, a silent corruption. Within safe
+  // range every step is exact, so the first departure is always caught.
+  if (!Number.isSafeInteger((value.seq0 as number) + payload.length - 1)) {
+    malformed(tag, 'member seqs must stay safe integers')
+  }
+  let time = value.time0 as number
+  for (const gap of data.dt as number[]) {
+    time += gap
+    if (!Number.isSafeInteger(time)) malformed(tag, 'member times must stay safe integers')
+  }
+  return value as unknown as ChunkRow
+}
+
+/** Expand a validated row back into its exact original events, in order. */
+function expandRow(row: ChunkRow): SessionEvent[] {
+  const members = row.type === 'tool-call-chunks' ? row.data.args : row.data.texts
+  const events: SessionEvent[] = []
+  let time = row.time0
+  for (let k = 0; k < members.length; k++) {
+    if (k > 0) time += row.data.dt[k - 1] as number
+    let chunk: StreamChunk
+    switch (row.type) {
+      case 'text-chunks':
+        chunk = { type: 'text-delta', index: row.data.index, text: members[k] as string }
+        break
+      case 'reasoning-chunks':
+        chunk = { type: 'reasoning-delta', index: row.data.index, text: members[k] as string }
+        break
+      case 'tool-call-chunks':
+        chunk = {
+          type: 'tool-call-delta',
+          index: row.data.index,
+          id: row.data.id,
+          ...Object.hasOwn(row.data, 'name') ? { name: row.data.name as string } : {},
+          argumentsDelta: members[k] as string,
+        }
+        break
+      /* v8 ignore next 2 -- validateRow only returns the three row tags */
+      default:
+        return assertNever(row, 'chunk-rows expandRow')
+    }
+    events.push({
+      type: 'assistant/chunk',
+      seq: row.seq0 + k,
+      time,
+      data: { turn: row.data.turn, step: row.data.step, chunk },
+    })
+  }
+  return events
+}
+
+/**
+ * Decode one parsed JSONL line value into the session event(s) it stores.
+ * Chunk-row-tagged values validate and expand (a malformed row throws — it is
+ * corrupt storage, and treating it as an event would silently drop a whole
+ * run); every other value passes through as a single event, unvalidated,
+ * exactly as readers treated event lines before packing existed.
+ *
+ * @param value - one line's `JSON.parse` result.
+ * @returns the stored events, in log order.
+ */
+export function decodeStorageRecord(value: unknown): SessionEvent[] {
+  if (!isRecord(value)) return [value as SessionEvent]
+  const tag = value.type
+  if (tag !== 'text-chunks' && tag !== 'reasoning-chunks' && tag !== 'tool-call-chunks') {
+    return [value as SessionEvent]
+  }
+  return expandRow(validateRow(value, tag))
+}
--- a/packages/core/session/src/index.ts
+++ b/packages/core/session/src/index.ts
@@ -23,6 +23,8 @@ export * from './types.ts'
 export { isJsonValue, snapshotJsonValue } from './json.ts'
 export type { JsonValue } from './json.ts'
 export { interruptedTurnClosers, TOOL_NOT_STARTED, TOOL_OUTCOME_UNKNOWN } from './repair.ts'
+export { decodeStorageRecord, packChunkRuns } from './chunk-rows.ts'
+export type { ChunkRow, StorageRecord } from './chunk-rows.ts'
 export type { SessionSurface, SurfaceFoldReplacement, SurfaceFoldResult } from './surface.ts'
 export { foldSurface, isSurfaceEvent, isSurfaceEligibleType } from './surface.ts'
 export { canonicalHeader, foldRequestHeader, headerEquals } from './request-header.ts'
--- a/packages/core/session/tests/chunk-rows.spec.ts
+++ b/packages/core/session/tests/chunk-rows.spec.ts
@@ -0,0 +1,236 @@
+/**
+ * Chunk-row codec tests: pack/expand round-trip losslessness (example-based and
+ * property-based), run-boundary rules, whitelist fall-through, and decoder
+ * validation failures.
+ */
+
+import { describe, expect, it } from 'vitest'
+import fc from 'fast-check'
+import { CallId } from '@deepseek-ai/dsh-llm'
+import type { StreamChunk } from '@deepseek-ai/dsh-llm'
+import { decodeStorageRecord, packChunkRuns } from '@deepseek-ai/dsh-session'
+import type { ChunkRow, SessionEvent, StorageRecord } from '@deepseek-ai/dsh-session'
+
+/** Build an `assistant/chunk` event with the exact live-append shape. */
+function chunkEvent(seq: number, time: number, chunk: StreamChunk, turn = 1, step = 1): SessionEvent {
+  return { type: 'assistant/chunk', seq, time, data: { turn, step, chunk } }
+}
+
+/** Sequential delta events (contiguous seqs, fixed 10ms gaps) of one kind. */
+function deltaRun(kind: 'text-delta' | 'reasoning-delta', count: number, seq0 = 0, index = 0): SessionEvent[] {
+  return Array.from({ length: count }, (_, k) =>
+    chunkEvent(seq0 + k, 1000 + 10 * k, { type: kind, index, text: `t${k}` }))
+}
+
+/** Decode a packed record list back to a flat event list. */
+function decodeAll(records: readonly StorageRecord[]): SessionEvent[] {
+  return records.flatMap(record => decodeStorageRecord(JSON.parse(JSON.stringify(record))))
+}
+
+describe('packChunkRuns', () => {
+  it('packs a text-delta run into one text-chunks row and round-trips it', () => {
+    const events = deltaRun('text-delta', 5)
+    const packed = packChunkRuns(events)
+    expect(packed).toHaveLength(1)
+    const row = packed[0] as ChunkRow
+    expect(row.type).toBe('text-chunks')
+    expect(row.seq0).toBe(0)
+    expect(row.time0).toBe(1000)
+    expect(row.data).toMatchObject({ turn: 1, step: 1, index: 0, dt: [10, 10, 10, 10], texts: ['t0', 't1', 't2', 't3', 't4'] })
+    expect(decodeAll(packed)).toStrictEqual(events)
+  })
+
+  it('packs reasoning and tool-call runs under their own tags', () => {
+    const reasoning = deltaRun('reasoning-delta', 3)
+    const toolCall = [4, 5, 6].map(seq =>
+      chunkEvent(seq, 1000 + seq, { type: 'tool-call-delta', index: 1, id: CallId('c1'), name: 'write', argumentsDelta: `a${seq}` }))
+    const packed = packChunkRuns([...reasoning, ...toolCall])
+    expect(packed.map(r => (r as ChunkRow).type)).toStrictEqual(['reasoning-chunks', 'tool-call-chunks'])
+    const row = packed[1] as ChunkRow & { type: 'tool-call-chunks' }
+    expect(row.data).toMatchObject({ id: 'c1', name: 'write', args: ['a4', 'a5', 'a6'] })
+    expect(decodeAll(packed)).toStrictEqual([...reasoning, ...toolCall])
+  })
+
+  it('packs a name-less tool-call run and round-trips field absence', () => {
+    const events = [0, 1, 2].map(seq =>
+      chunkEvent(seq, 1000, { type: 'tool-call-delta', index: 0, id: CallId('c1'), argumentsDelta: `a${seq}` }))
+    const packed = packChunkRuns(events)
+    expect(packed).toHaveLength(1)
+    expect(Object.hasOwn((packed[0] as ChunkRow).data, 'name')).toBe(false)
+    const decoded = decodeAll(packed)
+    expect(decoded).toStrictEqual(events)
+    expect(decoded.every(e => !Object.hasOwn((e.data as { chunk: object }).chunk, 'name'))).toBe(true)
+  })
+
+  it('leaves runs shorter than three events verbatim', () => {
+    const events = deltaRun('text-delta', 2)
+    expect(packChunkRuns(events)).toStrictEqual(events)
+  })
+
+  it('leaves non-delta chunks and non-chunk events verbatim between runs', () => {
+    const events: SessionEvent[] = [
+      chunkEvent(0, 1000, { type: 'block-start', index: 0, blockType: 'text' }),
+      ...deltaRun('text-delta', 3, 1),
+      chunkEvent(4, 1040, { type: 'block-end', index: 0, block: { type: 'text', text: 't0t1t2' } }),
+      { type: 'step/end', seq: 5, time: 1050, data: { turn: 1, step: 1 } },
+    ]
+    const packed = packChunkRuns(events)
+    expect(packed).toHaveLength(4)
+    expect((packed[1] as ChunkRow).type).toBe('text-chunks')
+    expect(decodeAll(packed)).toStrictEqual(events)
+  })
+
+  it.each([
+    ['a seq gap', deltaRun('text-delta', 3).map((e, k) => ({ ...e, seq: k === 2 ? 9 : e.seq }))],
+    ['a kind switch', [...deltaRun('text-delta', 2), ...deltaRun('reasoning-delta', 1, 2)]],
+    ['a block-index switch', [...deltaRun('text-delta', 2), ...deltaRun('text-delta', 1, 2, 7)]],
+    ['a step switch', deltaRun('text-delta', 3).map((e, k) => k === 2 ? chunkEvent(e.seq, e.time, (e.data as { chunk: StreamChunk }).chunk, 1, 2) : e)],
+  ])('breaks a run on %s (both halves too short to pack)', (_label, events) => {
+    expect(packChunkRuns(events as SessionEvent[])).toStrictEqual(events)
+  })
+
+  it('breaks a tool-call run on call-id or name change', () => {
+    const call = (seq: number, id: string, name?: string): SessionEvent =>
+      chunkEvent(seq, 1000, { type: 'tool-call-delta', index: 0, id: CallId(id), ...name !== undefined ? { name } : {}, argumentsDelta: 'a' })
+    const idSwitch = [call(0, 'c1', 'w'), call(1, 'c1', 'w'), call(2, 'c2', 'w')]
+    expect(packChunkRuns(idSwitch)).toStrictEqual(idSwitch)
+    const namePresence = [call(0, 'c1', 'w'), call(1, 'c1', 'w'), call(2, 'c1')]
+    expect(packChunkRuns(namePresence)).toStrictEqual(namePresence)
+  })
+
+  it('stores an off-whitelist delta verbatim (extra field, bad type, fractional time)', () => {
+    const extraField = { ...chunkEvent(0, 1000, { type: 'text-delta', index: 0, text: 'x' }), surfaceOp: 'append' }
+    const badText = chunkEvent(1, 1001, { type: 'text-delta', index: 0, text: 7 as unknown as string })
+    const fractionalTime = chunkEvent(2, 1001.5, { type: 'text-delta', index: 0, text: 'y' })
+    const events = [extraField, badText, fractionalTime] as SessionEvent[]
+    expect(packChunkRuns(events)).toStrictEqual(events)
+  })
+
+  it('breaks a run on a time gap beyond safe-integer range (subtraction would round)', () => {
+    // Both endpoints are safe integers, but their true difference (~2^54)
+    // exceeds exact double range: b - a rounds, so a + (b - a) !== b and a
+    // packed row would decode to a different timestamp.
+    const a = Number.MIN_SAFE_INTEGER
+    const b = Number.MAX_SAFE_INTEGER - 1
+    expect(a + (b - a)).not.toBe(b) // the rounding this guard exists for
+    const events = [
+      chunkEvent(0, a, { type: 'text-delta', index: 0, text: 'x' }),
+      chunkEvent(1, b, { type: 'text-delta', index: 0, text: 'y' }),
+      chunkEvent(2, b + 1, { type: 'text-delta', index: 0, text: 'z' }),
+    ]
+    expect(packChunkRuns(events)).toStrictEqual(events) // split at the gap; halves too short
+    expect(decodeAll(packChunkRuns(events))).toStrictEqual(events)
+  })
+
+  it('stores a delta with an off-whitelist data envelope verbatim (parsed-fixture shapes)', () => {
+    const mk = (seq: number, data: unknown): SessionEvent =>
+      ({ type: 'assistant/chunk', seq, time: 1000, data } as SessionEvent)
+    const events = [
+      mk(0, 'not-an-object'),
+      mk(1, { turn: 1, step: 1, chunk: { type: 'text-delta', index: 0, text: 'a' }, extra: 1 }),
+      mk(2, { turn: 'x', step: 1, chunk: { type: 'text-delta', index: 0, text: 'a' } }),
+      mk(3, { turn: 1, step: 1, chunk: 'not-an-object' }),
+      mk(4, { turn: 1, step: 1, chunk: { type: 'text-delta', index: 'x', text: 'a' } }),
+      mk(5, { turn: 1, step: 1, chunk: { type: 'tool-call-delta', index: 0, id: 7, argumentsDelta: 'a' } }),
+      mk(6, { turn: 1, step: 1, chunk: { type: 'tool-call-delta', index: 0, id: 'c', name: 7, argumentsDelta: 'a' } }),
+    ]
+    expect(packChunkRuns(events)).toStrictEqual(events)
+  })
+})
+
+describe('decodeStorageRecord', () => {
+  it('passes non-row values through as single events, unvalidated', () => {
+    const event = { type: 'turn/start', seq: 0, time: 1, data: { turn: 1 } }
+    expect(decodeStorageRecord(event)).toStrictEqual([event])
+    expect(decodeStorageRecord('junk')).toStrictEqual(['junk'])
+    expect(decodeStorageRecord(null)).toStrictEqual([null])
+  })
+
+  it('reconstructs timestamps through negative dt gaps (clock stepped back)', () => {
+    const events = [
+      chunkEvent(0, 1000, { type: 'text-delta', index: 0, text: 'a' }),
+      chunkEvent(1, 990, { type: 'text-delta', index: 0, text: 'b' }),
+      chunkEvent(2, 995, { type: 'text-delta', index: 0, text: 'c' }),
+    ]
+    expect(decodeAll(packChunkRuns(events))).toStrictEqual(events)
+  })
+
+  it.each([
+    ['a non-object data', { type: 'text-chunks', seq0: 0, time0: 1, data: 'x' }],
+    ['an envelope with extra keys', { type: 'text-chunks', seq0: 0, time0: 1, data: { turn: 1, step: 1, index: 0, dt: [], texts: ['a'] }, extra: 1 }],
+    ['a negative seq0', { type: 'text-chunks', seq0: -1, time0: 1, data: { turn: 1, step: 1, index: 0, dt: [], texts: ['a'] } }],
+    ['a non-finite time0', { type: 'text-chunks', seq0: 0, time0: Infinity, data: { turn: 1, step: 1, index: 0, dt: [], texts: ['a'] } }],
+    ['a fractional time0', { type: 'text-chunks', seq0: 0, time0: 1.5, data: { turn: 1, step: 1, index: 0, dt: [], texts: ['a'] } }],
+    ['a data shape mismatch', { type: 'text-chunks', seq0: 0, time0: 1, data: { turn: 1, step: 1, index: 0, dt: [], args: ['a'] } }],
+    ['a non-string member', { type: 'text-chunks', seq0: 0, time0: 1, data: { turn: 1, step: 1, index: 0, dt: [], texts: [7] } }],
+    ['an empty member list', { type: 'text-chunks', seq0: 0, time0: 1, data: { turn: 1, step: 1, index: 0, dt: [], texts: [] } }],
+    ['a dt arity mismatch', { type: 'text-chunks', seq0: 0, time0: 1, data: { turn: 1, step: 1, index: 0, dt: [1, 2], texts: ['a', 'b'] } }],
+    ['a non-finite dt gap', { type: 'text-chunks', seq0: 0, time0: 1, data: { turn: 1, step: 1, index: 0, dt: [NaN], texts: ['a', 'b'] } }],
+    ['a fractional dt gap', { type: 'text-chunks', seq0: 0, time0: 1, data: { turn: 1, step: 1, index: 0, dt: [0.5], texts: ['a', 'b'] } }],
+    ['a member seq leaving safe range', { type: 'text-chunks', seq0: Number.MAX_SAFE_INTEGER, time0: 1, data: { turn: 1, step: 1, index: 0, dt: [0, 0], texts: ['a', 'b', 'c'] } }],
+    ['a member time leaving safe range', { type: 'text-chunks', seq0: 0, time0: Number.MAX_SAFE_INTEGER, data: { turn: 1, step: 1, index: 0, dt: [1], texts: ['a', 'b'] } }],
+    ['a non-numeric turn', { type: 'text-chunks', seq0: 0, time0: 1, data: { turn: 'x', step: 1, index: 0, dt: [], texts: ['a'] } }],
+    ['a tool-call row without id', { type: 'tool-call-chunks', seq0: 0, time0: 1, data: { turn: 1, step: 1, index: 0, dt: [], args: ['a'] } }],
+    ['a tool-call row with non-string id', { type: 'tool-call-chunks', seq0: 0, time0: 1, data: { turn: 1, step: 1, index: 0, id: 7, dt: [], args: ['a'] } }],
+    ['a tool-call row with non-string name', { type: 'tool-call-chunks', seq0: 0, time0: 1, data: { turn: 1, step: 1, index: 0, id: 'c', name: 7, dt: [], args: ['a'] } }],
+  ])('throws on %s', (_label, row) => {
+    expect(() => decodeStorageRecord(row)).toThrow(/malformed .* storage row/)
+  })
+})
+
+// --- Property: pack∘decode is the identity over arbitrary event batches ---
+
+const deltaChunkArb: fc.Arbitrary<StreamChunk> = fc.oneof(
+  fc.record({ type: fc.constant<'text-delta'>('text-delta'), index: fc.nat(2), text: fc.string() }),
+  fc.record({ type: fc.constant<'reasoning-delta'>('reasoning-delta'), index: fc.nat(2), text: fc.string() }),
+  fc.record({
+    type: fc.constant<'tool-call-delta'>('tool-call-delta'),
+    index: fc.nat(2),
+    id: fc.constantFrom(CallId('c1'), CallId('c2')),
+    argumentsDelta: fc.string(),
+  }),
+  fc.record({
+    type: fc.constant<'tool-call-delta'>('tool-call-delta'),
+    index: fc.nat(2),
+    id: fc.constantFrom(CallId('c1'), CallId('c2')),
+    name: fc.constantFrom('write', 'read'),
+    argumentsDelta: fc.string(),
+  }),
+)
+
+const boundaryChunkArb: fc.Arbitrary<StreamChunk> = fc.oneof(
+  fc.record({ type: fc.constant<'block-start'>('block-start'), index: fc.nat(2), blockType: fc.constant<'text'>('text') }),
+  fc.record({ type: fc.constant<'finish'>('finish'), reason: fc.constant({ kind: 'stop' as const }) }),
+)
+
+/**
+ * Batches with contiguous seqs, arbitrary timestamps, mixed chunk kinds and
+ * turn/step placement. Times draw from the FULL safe-integer range (not just
+ * realistic clocks) so the property exercises the gap-overflow guard: two safe
+ * endpoints can differ by more than a double subtracts exactly.
+ */
+const batchArb: fc.Arbitrary<SessionEvent[]> = fc.array(
+  fc.record({
+    chunk: fc.oneof({ weight: 4, arbitrary: deltaChunkArb }, { weight: 1, arbitrary: boundaryChunkArb }),
+    time: fc.oneof(
+      { weight: 4, arbitrary: fc.integer({ min: 995, max: 9000 }) },
+      { weight: 1, arbitrary: fc.integer({ min: Number.MIN_SAFE_INTEGER, max: Number.MAX_SAFE_INTEGER }) },
+    ),
+    turn: fc.nat(1),
+    step: fc.nat(1),
+  }),
+  { maxLength: 40 },
+  // JSON round-trip normalizes fast-check's null-prototype records into the
+  // plain objects real log events are (the log is JSON), so equality compares
+  // values, not prototypes.
+).map(entries => JSON.parse(JSON.stringify(
+  entries.map((entry, k) => chunkEvent(k, entry.time, entry.chunk, entry.turn, entry.step)),
+)) as SessionEvent[])
+
+describe('chunk-row codec properties', () => {
+  it('JSON-serialized pack∘decode reproduces every batch exactly', () => {
+    fc.assert(fc.property(batchArb, (events) => {
+      expect(decodeAll(packChunkRuns(events))).toStrictEqual(events)
+    }))
+  })
+})
--- a/packages/examples/acp-demo/README.md
+++ b/packages/examples/acp-demo/README.md
@@ -43,6 +43,7 @@ The app owns this cluster through one ordered Cordis effect. Teardown drains the
 | `goals` | owner defaults | persisted goal-domain and model-tool config; `false` removes the goal stack and `/goal` producer |
 | `llmRetry` | owner defaults | bounded transient model-request retry policy routed through `dsh-agent-spine-demo` |
 | `persistenceRoot` | `./.sessions` | the JSONL backend's root directory |
+| `packChunks` | `false` | write delta-chunk runs as packed storage rows (the JSONL backend's `packChunks`) |
 | `persistenceCompression` | `'zstd'` | JSONL artifact encoding (`'zstd'` or raw `'none'`) |

 The leaf supplies the swappable backends: an LLM adapter (`llm-deepseek` for the real model, `llm-replay` for keyless snapshot replay), a bash executor, and optionally a `ctx.fs` provider. Workspace context becomes a no-op without `ctx.fs`; the shipped [`examples/acp-agent/cordis.yml`](../../../examples/acp-agent/cordis.yml) selects `dsh-sandbox-policy`, `dsh-fs-sandbox`, `dsh-fs-policy`, and `dsh-tool-fs` so baseline instructions and model-facing `read`/`write`/`edit` share one provider, sandbox mode, workspace root, and observed-version policy.
--- a/packages/examples/acp-demo/src/index.ts
+++ b/packages/examples/acp-demo/src/index.ts
@@ -57,6 +57,8 @@ export interface Config {
  sessionTitle?: NonNullable<agentCore.Config['sessionTitle']>
  /** Directory the JSONL session backend writes under. Defaults to `./.sessions`. */
  persistenceRoot?: string
+  /** Write delta-chunk runs as packed storage rows (the JSONL backend's `packChunks`). Defaults to `false`. */
+  packChunks?: boolean
  /** JSONL artifact encoding; defaults to checksummed Zstandard frames. */
  persistenceCompression?: JsonlCompression
  /** Controls automatic AGENTS.md/CLAUDE.md loading; configure a byte budget or set `false`. */
@@ -89,6 +91,7 @@ export const Config: z<Config> = z.object({
  dshHome: z.string(),
  sessionTitle: agentCore.SessionTitleConfigSchema,
  persistenceRoot: z.string().default(DEFAULT_PERSISTENCE_ROOT),
+  packChunks: z.boolean().default(false),
  persistenceCompression: JsonlCompressionSchema,
  workspaceContext: z.union([z.const(false), workspaceContext.Config]).required(),
  skills: agentCore.SkillConfigSchema,
@@ -115,10 +118,15 @@ export function apply(ctx: Context, config: Config): void {
    if (goals !== false) yield ctx.plugin(commandGoal).dispose
    yield ctx.plugin(agentCore, { ...agentCore.pickSpineConfig(config), goals }).dispose
    yield ctx.plugin(UserInteractionService).dispose
+    // Same rationale as the Config schema above: each front door forwards its own
+    // persistence passthroughs rather than sharing a facade with stdio-demo.
+    /* jscpd:ignore-start */
    yield ctx.plugin(SessionPersistenceJsonl, {
      root: config.persistenceRoot ?? DEFAULT_PERSISTENCE_ROOT,
+      ...config.packChunks !== undefined ? { packChunks: config.packChunks } : {},
      ...(config.persistenceCompression === undefined ? {} : { compression: config.persistenceCompression }),
    }).dispose
+    /* jscpd:ignore-end */
    yield ctx.plugin(sessionCheckpointPolicy).dispose
    yield ctx.plugin(acp, { provider: config.provider, model: config.model }).dispose
  }, 'acp-demo.composition')
--- a/packages/session-persistence/session-persistence-jsonl/README.md
+++ b/packages/session-persistence/session-persistence-jsonl/README.md
@@ -11,7 +11,8 @@ The JSONL durable session-persistence backend — a concrete `SessionPersistence
    <encoded-id>.jsonl           # only with compression: 'none'
 ```

- The first logical line is the immutable `SessionHeader` tagged `{ type: 'session', version, id, cwd?, createdAt, parentSession?, seedLength?, delegationDepth }`. `delegationDepth` is required on disk and is `0` for a top-level session; a missing or invalid value rejects the log. Every subsequent line is one `SessionEvent` JSON, **verbatim including `assistant/chunk`** so `seq` stays contiguous (`events[i].seq === i`).
+- The first logical line is the immutable `SessionHeader` tagged `{ type: 'session', version, id, cwd?, createdAt, parentSession?, seedLength?, delegationDepth }`. `delegationDepth` is required on disk and is `0` for a top-level session; a missing or invalid value rejects the log. Every subsequent logical line is one storage record; `assistant/chunk` events are never dropped, and `seq` stays contiguous across the decoded log (`events[i].seq === i`).
+- A storage record is a `SessionEvent` JSON verbatim, or — written only under `packChunks` — a **packed chunk row** (`text-chunks` / `reasoning-chunks` / `tool-call-chunks`; bare slash-less tags like the header's `session`, so row tags cannot be confused with event types): one line holding a run of ≥3 consecutive same-block `assistant/chunk` delta events, `seq0`/`time0` plus per-member `dt` gaps reconstructing every member's `seq`/`time` exactly. The lossless codec lives in `@deepseek-ai/dsh-session` (`packChunkRuns`/`decodeStorageRecord`) and whitelists exact shapes — anything unrecognized stores verbatim. Reading is layout-blind: `load` always decodes rows, so packed, unpacked, and mixed files load identically.
 - Session ids are unvalidated branded strings, so they are injectively escaped to a single safe path segment before use (no traversal, no collision).

 ## Config
@@ -19,6 +20,7 @@ The JSONL durable session-persistence backend — a concrete `SessionPersistence
 | Key | Type | Notes |
 |---|---|---|
 | `root` | `string` (required) | Root directory for all session files. **No default** — a `process.cwd()` default would scatter files as the process's cwd changes (bash calls, subprocesses). |
+| `packChunks` | `boolean` (default `false`) | Write delta-chunk runs as packed rows (~60% smaller logical logs measured on a real coding session). Off, the written logical layout is byte-identical to the pre-packing format; reading packed rows works regardless of this switch. Off by default while the snapshot goldens stay one-event-per-line — recording with packing on rewrites every fixture `session.jsonl`. |
 | `compression` | `'zstd' \| 'none'` | Defaults to `'zstd'`; `'none'` retains newline-delimited UTF-8 text. |

 `locate(meta)` returns `{ kind: 'jsonl', path }` using the resolved absolute root and the same cwd-bucket/id encoding as materialization. It performs no filesystem I/O: the target can be returned before the file exists, and an existing file contains only the last flushed prefix.
--- a/packages/session-persistence/session-persistence-jsonl/src/format.ts
+++ b/packages/session-persistence/session-persistence-jsonl/src/format.ts
@@ -10,7 +10,8 @@

 import { createHash } from 'node:crypto'
 import { join } from 'node:path'
-import type { SessionEvent, SessionHeader, SessionId } from '@deepseek-ai/dsh-session'
+import { decodeStorageRecord, packChunkRuns } from '@deepseek-ai/dsh-session'
+import type { SessionEvent, SessionHeader, SessionId, StorageRecord } from '@deepseek-ai/dsh-session'

 /** Physical encoding selected for JSONL session artifacts. */
 export type JsonlCompression = 'zstd' | 'none'
@@ -151,17 +152,26 @@ export function logPath(
 }

 /**
- * Serialize one event as a JSONL line (no trailing newline).
- * @param event - the event to serialize verbatim.
- * @returns the event's single-line JSON text; the writer adds the newline.
+ * Serialize an event batch as JSONL lines (no trailing newline). With
+ * `packChunks` on, delta-chunk runs pack into `text-chunks` /
+ * `reasoning-chunks` / `tool-call-chunks` storage rows; off writes one event
+ * per line, byte-identical to the pre-packing layout. Reading is layout-blind
+ * either way ({@link scanLog} always decodes rows), so the switch only shapes
+ * NEW bytes.
+ * @param events - the batch to serialize, in log order.
+ * @param packChunks - whether to pack delta runs into storage rows.
+ * @returns the batch's JSONL text; the writer adds the final newline.
 */
-export function eventLine(event: SessionEvent): string {
-  return JSON.stringify(event)
+export function eventLines(events: readonly SessionEvent[], packChunks: boolean): string {
+  const records: readonly StorageRecord[] = packChunks ? packChunkRuns(events) : events
+  return records.map(record => JSON.stringify(record)).join('\n')
 }

 /**
 * Parse a JSONL log buffer into its preserved event prefix (the header is line
- * 0). Fully written events in an interrupted final turn remain part of the
+ * 0). Event lines pass through verbatim; packed chunk rows expand back into
+ * their events, so callers see one contiguous event list regardless of layout.
+ * Fully written events in an interrupted final turn remain part of the
 * prefix. The first unparsable record or seq gap after the last `turn/end`
 * marks a tolerated torn tail; the same hole in the committed region rejects.
 *
@@ -200,46 +210,60 @@ export function scanLog(buffer: Buffer): { meta: SessionHeader; events: SessionE
  }
  const headerLine = parsedHeader

-  // Parse every complete record first so the last valid `turn/end` determines
-  // whether an earlier hole is committed corruption or an uncommitted tail.
-  interface Parsed { ok: boolean; event?: SessionEvent; endByte: number }
+  // Parse and decode every complete line first so the last valid `turn/end`
+  // determines whether an earlier hole is committed corruption or an
+  // uncommitted tail. One line yields one event, or a whole run for a packed
+  // chunk row; a row-tagged line that fails row validation is a hole, exactly
+  // like unparsable JSON.
+  interface Parsed { ok: boolean; events?: SessionEvent[]; endByte: number }
  const parsed: Parsed[] = eventEntries.map((entry) => {
    try {
-      return { ok: true, event: JSON.parse(entry.text) as SessionEvent, endByte: entry.endByte }
+      return { ok: true, events: decodeStorageRecord(JSON.parse(entry.text)), endByte: entry.endByte }
    } catch {
      return { ok: false, endByte: entry.endByte }
    }
  })

-  // The last index (into eventEntries) that is a valid `turn/end` — holes
-  // through a closed turn are always committed corruption.
+  // The last index (into eventEntries) that ends in a valid `turn/end` — the
+  // last fully-committed boundary (the loop flushes only at turn/end). A packed
+  // row never stores a turn/end, so only single-event lines can match.
  let lastTurnEnd = -1
  for (let i = parsed.length - 1; i >= 0; i--) {
    const p = parsed[i]
-    if (p?.ok && p.event?.type === 'turn/end') { lastTurnEnd = i; break }
+    if (p?.ok && p.events?.some(e => e.type === 'turn/end')) { lastTurnEnd = i; break }
  }

  // Preserve the contiguous prefix, including a complete interrupted turn;
  // holes through the last committed boundary throw, while later holes stop.
+  // Contiguity is a cursor over seqs (not the line index): a packed row
+  // advances the cursor by its whole run.
  const preserved: SessionEvent[] = []
-  for (let i = 0; i < parsed.length; i++) {
+  let lastPreservedLine = -1
+  scan: for (let i = 0; i < parsed.length; i++) {
    const p = parsed[i]
-    if (!p?.ok || p.event === undefined) {
+    if (!p?.ok || p.events === undefined) {
      if (i <= lastTurnEnd) throw new Error(`corrupt session log: unparsable committed event at line ${i + 1}`)
      break // torn tail fragment after the last turn/end — stop, tolerate
    }
-    if (p.event.seq !== i) {
-      if (i <= lastTurnEnd) throw new Error(`corrupt session log: seq gap in committed region at line ${i + 1} (expected ${i}, got ${p.event.seq})`)
-      break // gap after the last turn/end — torn tail, stop
+    for (const event of p.events) {
+      if (event.seq !== preserved.length) {
+        if (i <= lastTurnEnd) {
+          throw new Error(`corrupt session log: seq gap in committed region at line ${i + 1} (expected ${preserved.length}, got ${event.seq})`)
+        }
+        break scan // gap after the last turn/end — torn tail, stop
+      }
+      preserved.push(event)
    }
-    preserved.push(p.event)
+    lastPreservedLine = i
  }

-  // committedBytes = end of the last PRESERVED line (header if none): the next
-  // append truncates any torn bytes past this point before writing the
-  // synthetic closers + new events.
-  const lastPreserved = parsed[preserved.length - 1]
-  const committedBytes = preserved.length > 0 && lastPreserved ? lastPreserved.endByte : headerEntry.endByte
+  // committedBytes = end of the last FULLY preserved line (header if none): the
+  // next append truncates any torn bytes past this point before writing the
+  // synthetic closers + new events. A line is preserved whole or not at all —
+  // a mid-row seq gap discards the whole row, keeping the truncation offset on
+  // a line boundary.
+  const lastPreserved = parsed[lastPreservedLine]
+  const committedBytes = lastPreserved !== undefined ? lastPreserved.endByte : headerEntry.endByte
  return { meta: fromHeaderLine(headerLine), events: preserved, committedBytes }
 }

--- a/packages/session-persistence/session-persistence-jsonl/src/index.ts
+++ b/packages/session-persistence/session-persistence-jsonl/src/index.ts
@@ -17,7 +17,7 @@ import {
 } from '@deepseek-ai/dsh-session-persistence'
 import type { SessionEvent, SessionId, SessionHeader } from '@deepseek-ai/dsh-session'
 import {
-  encodeSegment, eventLine, logPath, logSuffix, parseHeaderMeta, scanLog, sessionDir, toHeaderLine,
+  encodeSegment, eventLines, logPath, logSuffix, parseHeaderMeta, scanLog, sessionDir, toHeaderLine,
  type JsonlCompression,
 } from './format.ts'
 import { compressZstdFrame, decompressZstdFrame, scanZstdFrames } from './zstd.ts'
@@ -33,7 +33,7 @@ export const JsonlCompressionSchema: z<JsonlCompression> = z.union([
  z.const('none'),
 ]).default(DEFAULT_COMPRESSION)

-/** Plugin config: where the JSONL backend keeps its session logs (`root` is required — no default). */
+/** Plugin config: where the JSONL backend keeps its session logs, and the packed-row write switch. */
 export interface Config {
  /**
   * Root directory for all session files. Required (no default): a default of
@@ -41,6 +41,15 @@ export interface Config {
   * (bash calls, subprocesses). Sessions group under per-cwd subdirectories.
   */
  root: string
+  /**
+   * Write runs of consecutive `assistant/chunk` delta events as packed
+   * `text-chunks`/`reasoning-chunks`/`tool-call-chunks` rows (lossless,
+   * ~60% smaller logs measured on a real session). Off by default while
+   * snapshot fixtures stay in the one-event-per-line layout: recording with
+   * packing on rewrites every golden `session.jsonl`. READING packed rows is
+   * unconditional — a log's layout never depends on this switch.
+   */
+  packChunks?: boolean
  /** Physical encoding; defaults to checksummed Zstandard frames. */
  compression?: JsonlCompression
 }
@@ -67,6 +76,7 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi

  static Config: z<Config> = z.object({
    root: z.string().required(),
+    packChunks: z.boolean().default(false),
    compression: JsonlCompressionSchema,
  })

@@ -78,6 +88,7 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
  override readonly name = 'session-persistence-jsonl'

  private root: string
+  private packChunks: boolean
  private compression: JsonlCompression
  private coordinator: PersistenceCoordinator<JsonlTornMarker>
  private rootEncodingCheck: Promise<void> | undefined
@@ -86,6 +97,9 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
    super(ctx)
    // Resolve once so later process.cwd() changes cannot split one backend across roots.
    this.root = resolve(config.root)
+    // schemastery (static Config) applied the default before construction;
+    // the cast records that runtime fact for exactOptionalPropertyTypes.
+    this.packChunks = (config as Required<Config>).packChunks
    this.compression = config.compression ?? DEFAULT_COMPRESSION
    this.coordinator = new PersistenceCoordinator<JsonlTornMarker>(this.ctx, this)
  }
@@ -354,7 +368,7 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
  /** Encode the header and first batch without combining their frame boundaries. */
  private async encodeMaterialization(meta: SessionHeader, events: readonly SessionEvent[]): Promise<Buffer | string> {
    const header = JSON.stringify(toHeaderLine(meta)) + '\n'
-    const body = events.map(eventLine).join('\n') + '\n'
+    const body = eventLines(events, this.packChunks) + '\n'
    if (this.compression === 'none') return header + body
    const headerFrame = await compressZstdFrame(header)
    const eventFrame = await compressZstdFrame(body)
@@ -363,7 +377,7 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi

  /** Encode one durable append batch in the configured physical representation. */
  private async encodeEventBatch(events: readonly SessionEvent[]): Promise<Buffer | string> {
-    const body = events.map(eventLine).join('\n') + '\n'
+    const body = eventLines(events, this.packChunks) + '\n'
    return this.compression === 'zstd' ? compressZstdFrame(body) : body
  }

--- a/packages/session-persistence/session-persistence-jsonl/tests/jsonl.spec.ts
+++ b/packages/session-persistence/session-persistence-jsonl/tests/jsonl.spec.ts
@@ -6,7 +6,7 @@ import { isAbsolute, join, relative, resolve } from 'node:path'
 import SessionStore, { SessionId } from '@deepseek-ai/dsh-session'
 import type { Session, SessionEvent, SessionHeader } from '@deepseek-ai/dsh-session'
 import SessionPersistenceJsonl from '@deepseek-ai/dsh-session-persistence-jsonl'
-import { encodeSegment, logPath, scanLog, sessionDir, toHeaderLine } from '../src/format.ts'
+import { encodeSegment, eventLines, logPath, scanLog, sessionDir, toHeaderLine } from '../src/format.ts'
 import { runPersistenceContract, meta, oneTurnLog, appendLog } from '../../session-persistence/tests/contract.ts'
 import { runCoordinatorContract, type CoordinatorFixture } from '../../session-persistence/tests/coordinator-contract.ts'

@@ -554,6 +554,121 @@ describe('SessionPersistenceJsonl: scanLog unit', () => {
  })
 })

+describe('SessionPersistenceJsonl: packed chunk rows (packChunks: true)', () => {
+  let ctx: Context
+  beforeEach(async () => {
+    root = await freshRoot()
+    ctx = new Context()
+    await ctx.plugin(SessionStore)
+    // compression: 'none' — these tests assert the textual storage-record layout
+    // (row tags per line); packing is orthogonal to the physical encoding.
+    await ctx.plugin(SessionPersistenceJsonl, { root, packChunks: true, compression: 'none' })
+  })
+  afterEach(async () => { await ctx.fiber.dispose() })
+
+  /** A one-turn log whose step streams a five-member text-delta run. */
+  function chunkRunLog(): SessionEvent[] {
+    const deltas: SessionEvent[] = Array.from({ length: 5 }, (_, k) => ({
+      type: 'assistant/chunk',
+      seq: 2 + k,
+      time: 3 + k,
+      data: { turn: 1, step: 1, chunk: { type: 'text-delta', index: 0, text: `t${k}` } },
+    }))
+    return [
+      { type: 'turn/start', seq: 0, time: 1, data: { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } } },
+      { type: 'step/start', seq: 1, time: 2, data: { turn: 1, step: 1 } },
+      ...deltas,
+      { type: 'assistant/message', seq: 7, time: 8, data: { turn: 1, step: 1, content: [{ type: 'text', text: 't0t1t2t3t4' }], provenance: { provider: 'mock', model: 'mock' } }, surfaceOp: 'append', sourceEventSeqs: [2, 3, 4, 5, 6] },
+      { type: 'step/end', seq: 8, time: 9, data: { turn: 1, step: 1 } },
+      { type: 'turn/end', seq: 9, time: 10, data: { turn: 1, reason: { kind: 'completed' } } },
+    ]
+  }
+
+  it('writes a delta run as one text-chunks row and loads back identical events', async () => {
+    const m = meta('packed', '/work')
+    const log = chunkRunLog()
+    await ctx.sessionPersistence.create(m)
+    await ctx.sessionPersistence.append(m.id, log)
+
+    const raw = (await readFile(rawLogPath(root, '/work', m.id), 'utf8')).split('\n').filter(Boolean)
+    const tags = raw.slice(1).map(line => (JSON.parse(line) as { type: string }).type)
+    expect(tags).toEqual(['turn/start', 'step/start', 'text-chunks', 'assistant/message', 'step/end', 'turn/end'])
+
+    const loaded = await ctx.sessionPersistence.load(m.id)
+    expect(loaded.events).toEqual(log)
+  })
+
+  it('loads a mixed file: verbatim lines from an unpacked writer, then packed appends', async () => {
+    const m = meta('mixed', '/work')
+    const log = chunkRunLog()
+    // First turn written line-per-event by an unpacked-config writer (an old
+    // file, hand-planted so this packed-config backend adopts it on load).
+    await mkdir(sessionDir(root, '/work'), { recursive: true })
+    await writeFile(rawLogPath(root, '/work', m.id), [
+      JSON.stringify({ type: 'session', version: 0, id: 'mixed', createdAt: 1000, cwd: '/work', delegationDepth: 0 }),
+      ...log.map(e => JSON.stringify(e)),
+    ].join('\n') + '\n')
+    // Adopt the stored log (cursor = stored length), then append a second turn
+    // through THIS packed-config backend.
+    expect((await ctx.sessionPersistence.load(m.id)).events).toEqual(log)
+    const secondTurn: SessionEvent[] = JSON.parse(JSON.stringify(log)) as SessionEvent[]
+    for (const [k, e] of secondTurn.entries()) {
+      ;(e as { seq: number }).seq = 10 + k
+      ;(e.data as { turn: number }).turn = 2
+    }
+    await ctx.sessionPersistence.append(m.id, secondTurn)
+
+    const loaded = await ctx.sessionPersistence.load(m.id)
+    expect(loaded.events).toEqual([...log, ...secondTurn])
+    // The packed append really packed: the file's tail carries a text-chunks row.
+    const tags = (await readFile(rawLogPath(root, '/work', m.id), 'utf8')).split('\n').filter(Boolean)
+      .map(line => (JSON.parse(line) as { type: string }).type)
+    expect(tags.filter(t => t === 'text-chunks')).toHaveLength(1)
+    expect(tags.filter(t => t === 'assistant/chunk')).toHaveLength(5)
+  })
+
+  it('scanLog: a packed row advances the seq cursor by its whole run', () => {
+    const logText = [
+      JSON.stringify({ type: 'session', version: 0, id: 'rows', createdAt: 1, delegationDepth: 0 }),
+      JSON.stringify({ type: 'turn/start', seq: 0, time: 1, data: { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } } }),
+      JSON.stringify({ type: 'text-chunks', seq0: 1, time0: 2, data: { turn: 1, step: 1, index: 0, dt: [1, 1], texts: ['a', 'b', 'c'] } }),
+      JSON.stringify({ type: 'turn/end', seq: 4, time: 5, data: { turn: 1, reason: { kind: 'completed' } } }),
+    ].join('\n') + '\n'
+    const { events } = scanLog(Buffer.from(logText))
+    expect(events.map(e => e.seq)).toEqual([0, 1, 2, 3, 4])
+    expect(events[2]).toEqual({ type: 'assistant/chunk', seq: 2, time: 3, data: { turn: 1, step: 1, chunk: { type: 'text-delta', index: 0, text: 'b' } } })
+  })
+
+  it('scanLog: a malformed packed row in the committed region rejects like corrupt JSON', () => {
+    const logText = [
+      JSON.stringify({ type: 'session', version: 0, id: 'bad-row', createdAt: 1, delegationDepth: 0 }),
+      // dt arity mismatch — row validation throws, so the line is a committed hole.
+      JSON.stringify({ type: 'text-chunks', seq0: 0, time0: 1, data: { turn: 1, step: 1, index: 0, dt: [], texts: ['a', 'b'] } }),
+      JSON.stringify({ type: 'turn/end', seq: 2, time: 3, data: { turn: 1, reason: { kind: 'completed' } } }),
+    ].join('\n') + '\n'
+    expect(() => scanLog(Buffer.from(logText))).toThrow(/unparsable committed event/)
+  })
+
+  it('scanLog: a packed row with a mid-run seq gap after the last turn/end drops the whole row', () => {
+    const logText = [
+      JSON.stringify({ type: 'session', version: 0, id: 'row-gap', createdAt: 1, delegationDepth: 0 }),
+      JSON.stringify({ type: 'turn/start', seq: 0, time: 1, data: { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } } }),
+      // seq0 skips 1 — the run's first member is already a gap; no turn/end follows.
+      JSON.stringify({ type: 'text-chunks', seq0: 2, time0: 2, data: { turn: 1, step: 1, index: 0, dt: [1, 1], texts: ['a', 'b', 'c'] } }),
+    ].join('\n') + '\n'
+    const scanned = scanLog(Buffer.from(logText))
+    expect(scanned.events.map(e => e.seq)).toEqual([0])
+    // committedBytes stays on the line boundary BEFORE the dropped row.
+    const headerAndTurn = logText.split('\n').slice(0, 2).join('\n') + '\n'
+    expect(scanned.committedBytes).toBe(Buffer.byteLength(headerAndTurn, 'utf8'))
+  })
+
+  it('eventLines(packChunks: false) is byte-identical to the pre-packing layout', () => {
+    const log = chunkRunLog()
+    expect(eventLines(log, false)).toBe(log.map(e => JSON.stringify(e)).join('\n'))
+  })
+})
+
 describe('SessionPersistenceJsonl: edge cases', () => {
  let ctx: Context
  beforeEach(async () => {
--- a/packages/session-persistence/session-persistence-jsonl/tests/zstd.spec.ts
+++ b/packages/session-persistence/session-persistence-jsonl/tests/zstd.spec.ts
@@ -7,7 +7,7 @@ import { join } from 'node:path'
 import SessionStore, { SessionId } from '@deepseek-ai/dsh-session'
 import type { SessionEvent } from '@deepseek-ai/dsh-session'
 import SessionPersistenceJsonl from '@deepseek-ai/dsh-session-persistence-jsonl'
-import { eventLine, logPath, scanLog, sessionDir, toHeaderLine, type JsonlCompression } from '../src/format.ts'
+import { logPath, scanLog, sessionDir, toHeaderLine, type JsonlCompression } from '../src/format.ts'
 import { compressZstdFrame, decompressZstdFrame, scanZstdFrames } from '../src/zstd.ts'
 import { runPersistenceContract, meta, oneTurnLog } from '../../session-persistence/tests/contract.ts'
 import { runCoordinatorContract, type CoordinatorFixture } from '../../session-persistence/tests/coordinator-contract.ts'
@@ -217,7 +217,7 @@ describe('SessionPersistenceJsonl: default Zstandard encoding', () => {
    const plaintext = await decodeCompleteFrames(buffer)
    expect(plaintext.toString()).toBe([
      JSON.stringify(toHeaderLine(header)),
-      ...oneTurnLog().map(eventLine),
+      ...oneTurnLog().map(e => JSON.stringify(e)),
      '',
    ].join('\n'))
    expect((await ctx.sessionPersistence.load(header.id)).events).toEqual(oneTurnLog())
@@ -288,7 +288,7 @@ describe('SessionPersistenceJsonl: default Zstandard encoding', () => {
      { type: 'step/start', seq: 7, time: 8, data: { turn: 2, step: 1 } },
      { type: 'assistant/chunk', seq: 8, time: 9, data: { turn: 2, step: 1, chunk: { type: 'text-delta', index: 0, text: deterministicNoise(300_000) } } },
    ] as SessionEvent[]
-    const plaintext = openTurn.map(eventLine).join('\n') + '\n'
+    const plaintext = openTurn.map(e => JSON.stringify(e)).join('\n') + '\n'
    const partial = await tornFrame(plaintext, (decoded) => {
      const newlines = decoded.match(/\n/g)?.length ?? 0
      return newlines >= 2 && !decoded.endsWith('\n')
@@ -334,7 +334,7 @@ describe('SessionPersistenceJsonl: default Zstandard encoding', () => {
      { type: 'turn/start', seq: 6, time: 7, data: { turn: 2, trigger: { kind: 'message', source: { kind: 'user' } } } },
      { type: 'turn/end', seq: 7, time: 8, data: { turn: 2, reason: { kind: 'completed' } } },
    ] as SessionEvent[]
-    const frame = await compressZstdFrame(secondTurn.map(eventLine).join('\n') + '\n')
+    const frame = await compressZstdFrame(secondTurn.map(e => JSON.stringify(e)).join('\n') + '\n')
    await appendFile(path, frame.subarray(0, -1))

    const loaded = await ctx.sessionPersistence.load(header.id)
@@ -456,7 +456,7 @@ describe('SessionPersistenceJsonl: encoding selection', () => {
    await mkdir(sessionDir(root, loadHeader.cwd), { recursive: true })
    await writeFile(logPath(root, loadHeader.cwd, loadHeader.id, 'none'), [
      JSON.stringify(toHeaderLine(loadHeader)),
-      ...oneTurnLog().map(eventLine),
+      ...oneTurnLog().map(e => JSON.stringify(e)),
      '',
    ].join('\n'))
    await expect(ctx.sessionPersistence.load(loadHeader.id)).rejects.toThrow(/uses \.jsonl/)
@@ -474,7 +474,7 @@ describe('SessionPersistenceJsonl: encoding selection', () => {
    await mkdir(sessionDir(root, header.cwd), { recursive: true })
    await writeFile(logPath(root, header.cwd, header.id, 'none'), [
      JSON.stringify(toHeaderLine(header)),
-      ...oneTurnLog().map(eventLine),
+      ...oneTurnLog().map(e => JSON.stringify(e)),
      '',
    ].join('\n'))
    await expect(ctx.sessionPersistence.append(header.id, oneTurnLog())).rejects.toThrow(/uses \.jsonl/)
--- a/packages/support/acp-snapshot/README.md
+++ b/packages/support/acp-snapshot/README.md
@@ -7,7 +7,7 @@ Four layers, importable separately:
 - **`launchAcpTestAgent` (launcher)** — boots a source agent under tsx or a built `lib` agent under plain Node from a supplied cwd, connects the SDK client over a raw-byte stdout tee, collects session updates and stderr, surfaces asynchronous spawn failures through startup, fails closed on unhandled permission requests, and owns graceful or signalled shutdown. Shutdown waits for process exit, inherited stdio closure, and ACP parser exhaustion before resolving or propagating a child error, so captures are complete and callers can remove owned paths after either outcome. When Windows accepts forced termination but publishes its exit marker asynchronously, shutdown gives that marker a bounded grace before treating fallback refusal as a second failure. Snapshot and ordinary e2e suites share this process boundary; a test supplies only agent paths, cwd, environment overrides, and any permission policy.
 - **`runScenario` (harness)** — drives ACP JSON-RPC stdio from a deterministic `input.json` script through the launcher, tees raw stdout for the expected-output and purity checks, and harvests every persisted raw JSONL session log (parent and subagent children, primary-first) after graceful stdin EOF. `AgentUnderTest` supplies absolute `binScript`, optional `libBinScript`, `configPath`, and `tsconfigPath` paths because the subprocess cwd is outside the repo; `workspaceParent` may move the generated child cwd from the platform temp directory when that grant is itself under test. Startup failures preserve captured agent stderr in the rejected diagnostic.
 - **Normalizers** — pure functions turning the two captured surfaces into stable text: `normalizeStdout` (JSON-RPC ids → first-seen sequence; UUIDs/cwd → tokens; cwd-rooted separators selected as canonical `/` or host-native; `session_info_update.updatedAt` → `{{updatedAt}}`; doubles as the stdout-purity check), `normalizeSessionLog` (times zeroed, `seq` kept, the same cwd-path policy), `scrubSystemPrompts` (prompt text → `{{system}}`), `scrubToolSchemas` (schema bulk → `{{tools}}`), and `scrubRequestHeaders` (all header bulk → `{{system}}`/`{{tools}}`/`{{messagePrefix}}` outside each pin, structure kept — [pinned-header Agent Note](../../../.agents/notes/implemented/testing/2026-07-06-pin-request-header-content-in-one-scenario.md)).
- **`defineAcpSnapshotSuite` (factory)** — registers the whole describe/it tree for a scenario table: per-scenario expected-output and re-persisted-log comparisons, record/refresh fixture write-back, rejection of structured `UNKNOWN_TOOL` results, the per-header-class pin (`system-prompt.expected.md` plus `tool-schemas.expected.json`) with its live uniformity guard, and the fixture guard block (no orphan scenario dirs, required files present, exactly one pin per class, every JSONL prompt/schema-scrubbed, non-pinning fixtures fully header-scrubbed). Refresh preserves existing volatile fields by event position and gives a newly inserted `session/title` its preceding event's time, so feature-driven insertions do not churn the remainder of a fixture. Each scenario directory's `session.jsonl` plus contiguous `session.<n>.jsonl` siblings are the ordered primary/child inventory; the scenario table does not duplicate their count. Must be called at vitest collection time.
+- **`defineAcpSnapshotSuite` (factory)** — registers the whole describe/it tree for a scenario table: per-scenario expected-output and re-persisted-log comparisons, record/refresh fixture write-back, rejection of structured `UNKNOWN_TOOL` results, the per-header-class pin (`system-prompt.expected.md` plus `tool-schemas.expected.json`) with its live uniformity guard, and the fixture guard block (no orphan scenario dirs, required files present, exactly one pin per class, every JSONL prompt/schema-scrubbed, non-pinning fixtures fully header-scrubbed). Refresh expands packed timing envelopes before aligning existing volatile event times, so switching between packed and unpacked layouts cannot shift later records; fresh chunk-fragment arrays remain authoritative. A newly inserted `session/title` receives its preceding event's time so feature-driven insertions do not churn the remainder of a fixture. Each scenario directory's `session.jsonl` plus contiguous `session.<n>.jsonl` siblings are the ordered primary/child inventory; the scenario table does not duplicate their count. Must be called at vitest collection time.

 A consuming `*.snapshot.ts` is the scenario table plus one factory call:

--- a/packages/support/acp-snapshot/src/normalize.ts
+++ b/packages/support/acp-snapshot/src/normalize.ts
@@ -135,8 +135,10 @@ export function normalizeStdout(
 * Normalize a session JSONL log into a stable expected output: the header line's
 * volatile fields (`createdAt`, `id`, `cwd`) and every event's `time` are
 * zeroed/scrubbed, all volatile strings scrubbed, and `seq` is LEFT INTACT
- * (deterministic by contract). Output is JSONL in the same shape as the input —
- * one compact record per line.
+ * (deterministic by contract). A packed chunk row's timing (`time0`, the `dt`
+ * gaps) zeroes just like an event `time`; its `seq0` stays, like `seq`.
+ * Output is JSONL in the same shape as the input — one compact record per
+ * line.
 *
 * @param rawLog The raw session `.jsonl` content.
 * @param ctx The run's volatile values to scrub.
@@ -155,6 +157,13 @@ export function normalizeSessionLog(
    // Header line: { type: 'session', createdAt, id, cwd, … }.
    if (record.type === 'session') {
      if ('createdAt' in record) record.createdAt = 0
+    } else if ('time0' in record) {
+      // Packed chunk row: zero the anchor timestamp and every member gap.
+      record.time0 = 0
+      const data = record.data
+      if (data !== null && typeof data === 'object' && Array.isArray((data as { dt?: unknown }).dt)) {
+        (data as { dt: unknown[] }).dt = (data as { dt: unknown[] }).dt.map(() => 0)
+      }
    } else if ('time' in record) {
      // Event line: zero the epoch-ms timestamp; keep seq (deterministic).
      record.time = 0
--- a/packages/support/acp-snapshot/src/suite.ts
+++ b/packages/support/acp-snapshot/src/suite.ts
@@ -42,6 +42,8 @@ const WINDOWS_STDOUT_SNAPSHOT = 'stdout.expected.windows.jsonl'
 /** Stable session-log token standing in for the sidecar's initial schemas. */
 const TOOLS_TOKEN = '{{tools}}'

+const PACKED_CHUNK_ROW_TYPES = new Set(['text-chunks', 'reasoning-chunks', 'tool-call-chunks'])
+
 /** A snapshot scenario and how its fixtures are produced. */
 export interface Scenario {
  name: string
@@ -404,6 +406,23 @@ function parseJsonlRecords(text: string): Record<string, unknown>[] {
    .map(line => JSON.parse(line) as Record<string, unknown>)
 }

+/** One packed row's member times, or `undefined` for an ordinary record. */
+function packedTimes(record: Record<string, unknown>): number[] | undefined {
+  if (!PACKED_CHUNK_ROW_TYPES.has(record.type as string)) return undefined
+  const row = record as unknown as { time0: number; data: { dt: number[] } }
+  const times = [row.time0]
+  for (const gap of row.data.dt) times.push((times[times.length - 1] as number) + gap)
+  return times
+}
+
+/** Expand packed timing envelopes so refresh alignment follows logical events, not physical lines. */
+function logicalRecords(records: Record<string, unknown>[]): Record<string, unknown>[] {
+  return records.flatMap((record) => {
+    const times = packedTimes(record)
+    return times === undefined ? [record] : times.map(time => ({ type: 'assistant/chunk', time }))
+  })
+}
+
 /**
 * Find tool calls whose structured result reports `UNKNOWN_TOOL`.
 *
@@ -469,11 +488,32 @@ function preserveFixtureVolatiles(record: Record<string, unknown>, existing: Rec
  }
 }

+/** Carry logical member times into a fresh packed row while leaving its fragment arrays untouched. */
+function preservePackedMemberTimes(
+  record: Record<string, unknown>,
+  existingMembers: Record<string, unknown>[],
+): void {
+  if (!PACKED_CHUNK_ROW_TYPES.has(record.type as string)) return
+  const row = record as unknown as { time0: number; data: { dt: number[] } }
+  const firstTime = existingMembers[0]?.time
+  if (!Number.isSafeInteger(firstTime)) return
+  row.time0 = firstTime as number
+  if (existingMembers.length !== row.data.dt.length + 1) return
+  const times = existingMembers.map(member => Number.isSafeInteger(member.time) ? member.time as number : undefined)
+  if (times.some(time => time === undefined)) return
+  const memberTimes = times as number[]
+  const gaps = memberTimes.slice(1).map((time, index) => time - (memberTimes[index] as number))
+  if (gaps.some(gap => !Number.isSafeInteger(gap))) return
+  row.data.dt = gaps
+}
+
 /**
 * Rewrite a fresh replay-produced log so repeated refreshes do not churn
 * volatile fixture fields. Meaningful event payloads come from `fresh`; the
- * existing fixture lends session ids, cwd, creation times, event times, and
- * hook durations where the record shape still matches.
+ * existing fixture lends session ids, cwd, creation times, logical event
+ * times, and hook durations where the record shape still matches. Packed
+ * timing envelopes expand for alignment, so packing does not shift later
+ * records; fresh fragment arrays remain authoritative.
 *
 * @param fresh The newly harvested session JSONL.
 * @param existing The committed fixture JSONL being refreshed.
@@ -483,21 +523,23 @@ function preserveFixtureVolatiles(record: Record<string, unknown>, existing: Rec
 export function stabilizeRefreshLog(fresh: string, existing: string, replacements: FixtureReplacement[]): string {
  let stable = fresh
  for (const { from, to } of replacements) stable = stable.split(from).join(to)
-  const existingRecords = parseJsonlRecords(existing)
+  const existingRecords = logicalRecords(parseJsonlRecords(existing))
  const records = parseJsonlRecords(stable)
  let existingIndex = 0
  let previousEventTime: unknown
  for (let i = 0; i < records.length; i++) {
    const record = records[i] as Record<string, unknown>
    const existingRecord = existingRecords[existingIndex]
+    const memberCount = packedTimes(record)?.length ?? 1
    const insertedTitle = record.type === 'session/title' && existingRecord?.type !== 'session/title'
    if (insertedTitle) {
      /* v8 ignore next -- a title is turn-enclosed, so a preceding event time exists in every valid fixture. */
      if (typeof previousEventTime !== 'number') throw new Error('acp-snapshot: inserted title has no preceding event time')
      record.time = previousEventTime
    } else {
+      preservePackedMemberTimes(record, existingRecords.slice(existingIndex, existingIndex + memberCount))
      preserveFixtureVolatiles(record, existingRecord)
-      existingIndex += 1
+      existingIndex += memberCount
    }
    if (typeof record.time === 'number') previousEventTime = record.time
  }
--- a/packages/support/acp-snapshot/tests/normalize.spec.ts
+++ b/packages/support/acp-snapshot/tests/normalize.spec.ts
@@ -265,6 +265,27 @@ describe('normalizeSessionLog', () => {
    expect(out).toContain('"decision":"block"') // the decision is the behavior — kept
  })

+  it('zeroes a packed chunk row\'s time0 and dt gaps but keeps seq0 and payload', () => {
+    const row = JSON.stringify({
+      type: 'text-chunks', seq0: 7, time0: 999,
+      data: { turn: 1, step: 1, index: 0, dt: [212, 27, 0], texts: ['a', 'b', 'c', 'd'] },
+    })
+    const out = normalizeSessionLog(`${header({})}\n${row}\n`, ctx)
+    expect(out).toContain('"time0":0')
+    expect(out).toContain('"dt":[0,0,0]')
+    expect(out).toContain('"seq0":7') // seq0 is deterministic, like seq — NOT scrubbed
+    expect(out).toContain('"texts":["a","b","c","d"]')
+    expect(out).not.toContain('999')
+    expect(out).not.toContain('212')
+  })
+
+  it('zeroes time0 even when a malformed row carries no dt array', () => {
+    const row = JSON.stringify({ type: 'text-chunks', seq0: 1, time0: 999, data: 'not-an-object' })
+    const out = normalizeSessionLog(`${header({})}\n${row}\n`, ctx)
+    expect(out).toContain('"time0":0')
+    expect(out).not.toContain('999')
+  })
+
  it('leaves a non-hook event durationMs untouched (only hook/result is scrubbed)', () => {
    const ev = JSON.stringify({ type: 'tool/result', seq: 2, time: 5, data: { durationMs: 88 } })
    const out = normalizeSessionLog(`${header({})}\n${ev}\n`, ctx)
--- a/packages/support/acp-snapshot/tests/suite.spec.ts
+++ b/packages/support/acp-snapshot/tests/suite.spec.ts
@@ -458,6 +458,76 @@ describe('refreshFixtureReplacements', () => {
 })

 describe('stabilizeRefreshLog', () => {
+  it('preserves unpacked member times when refresh first packs a chunk run', () => {
+    const fresh = [
+      '{"type":"session","id":"same","createdAt":200}',
+      '{"type":"reasoning-chunks","seq0":2,"time0":200,"data":{"turn":1,"step":1,"index":0,"dt":[5,7],"texts":["new",""," split"]}}',
+      '{"type":"assistant/message","seq":5,"time":220,"data":{}}',
+      '',
+    ].join('\n')
+    const existing = [
+      '{"type":"session","id":"same","createdAt":100}',
+      '{"type":"assistant/chunk","seq":2,"time":100,"data":{"turn":1,"step":1,"chunk":{"type":"reasoning-delta","index":0,"text":"old"}}}',
+      '{"type":"assistant/chunk","seq":3,"time":101,"data":{"turn":1,"step":1,"chunk":{"type":"reasoning-delta","index":0,"text":"chunk"}}}',
+      '{"type":"assistant/chunk","seq":4,"time":103,"data":{"turn":1,"step":1,"chunk":{"type":"reasoning-delta","index":0,"text":"shape"}}}',
+      '{"type":"assistant/message","seq":5,"time":104,"data":{}}',
+      '',
+    ].join('\n')
+
+    expect(stabilizeRefreshLog(fresh, existing, [])).toBe([
+      '{"type":"session","id":"same","createdAt":100}',
+      '{"type":"reasoning-chunks","seq0":2,"time0":100,"data":{"turn":1,"step":1,"index":0,"dt":[1,2],"texts":["new",""," split"]}}',
+      '{"type":"assistant/message","seq":5,"time":104,"data":{}}',
+      '',
+    ].join('\n'))
+  })
+
+  it('preserves packed member times without flattening fresh chunk boundaries', () => {
+    const fresh = [
+      '{"type":"session","id":"same","createdAt":200}',
+      '{"type":"text-chunks","seq0":2,"time0":200,"data":{"turn":1,"step":1,"index":0,"dt":[5,7],"texts":["new",""," split"]}}',
+      '',
+    ].join('\n')
+    const existing = [
+      '{"type":"session","id":"same","createdAt":100}',
+      '{"type":"text-chunks","seq0":2,"time0":100,"data":{"turn":1,"step":1,"index":0,"dt":[1,2],"texts":["old","chunk","shape"]}}',
+      '',
+    ].join('\n')
+
+    expect(stabilizeRefreshLog(fresh, existing, [])).toBe([
+      '{"type":"session","id":"same","createdAt":100}',
+      '{"type":"text-chunks","seq0":2,"time0":100,"data":{"turn":1,"step":1,"index":0,"dt":[1,2],"texts":["new",""," split"]}}',
+      '',
+    ].join('\n'))
+  })
+
+  it.each([
+    ['the old run is absent', [], 200],
+    ['the old run is shorter', [100, 101], 100],
+    ['a later old time is invalid', [100, 'invalid', 103], 100],
+    ['an old gap is not exactly representable', [Number.MIN_SAFE_INTEGER, Number.MAX_SAFE_INTEGER - 1, Number.MAX_SAFE_INTEGER - 1], Number.MIN_SAFE_INTEGER],
+  ])('keeps fresh packed gaps when %s', (_case, existingTimes, expectedTime0) => {
+    const freshRow = {
+      type: 'reasoning-chunks',
+      seq0: 2,
+      time0: 200,
+      data: { turn: 1, step: 1, index: 0, dt: [5, 7], texts: ['new', '', ' split'] },
+    }
+    const existingRows = existingTimes.map((time, index) => ({
+      type: 'assistant/chunk',
+      seq: index + 2,
+      time,
+      data: {},
+    }))
+    const output = stabilizeRefreshLog(
+      `${JSON.stringify({ type: 'session', id: 'same', createdAt: 200 })}\n${JSON.stringify(freshRow)}\n`,
+      `${JSON.stringify({ type: 'session', id: 'same', createdAt: 100 })}\n${existingRows.map(row => JSON.stringify(row)).join('\n')}\n`,
+      [],
+    ).trim().split('\n').map(line => JSON.parse(line) as Record<string, unknown>)
+
+    expect(output[1]).toStrictEqual({ ...freshRow, time0: expectedTime0 })
+  })
+
  it('aligns volatile times across a newly inserted log event', () => {
    const fresh = [
      '{"type":"session","id":"same","createdAt":200}',
--- a/packages/support/llm-replay/src/index.ts
+++ b/packages/support/llm-replay/src/index.ts
@@ -9,6 +9,7 @@
 import { existsSync, readFileSync } from 'node:fs'
 import { delimiter as pathDelimiter } from 'node:path'
 import type { Context } from 'cordis'
+import { decodeStorageRecord } from '@deepseek-ai/dsh-session'
 import type { SessionEvent } from '@deepseek-ai/dsh-session'
 import type { GenerateOptions, LlmModelContext, LlmModelInfo, LlmProviderInfo, StreamChunk } from '@deepseek-ai/dsh-llm'
 import { LlmAdapter, LlmError, assertNever } from '@deepseek-ai/dsh-llm'
@@ -96,7 +97,9 @@ export interface SessionScript {
 /**
 * Parse a session `.jsonl` buffer into its event list. Line 0 is the session
 * header (a `{type:'session',…}` record), every subsequent non-empty line is a
- * {@link SessionEvent}. The header is skipped; malformed lines fail loud.
+ * {@link SessionEvent} or a packed chunk row (expanded back into its events, so
+ * a fixture recorded with `packChunks` on derives the same script). The header
+ * is skipped; malformed lines fail loud.
 * @param text - the raw `.jsonl` file contents.
 * @returns every event after the header, in log order.
 */
@@ -105,8 +108,7 @@ export function parseSessionLog(text: string): SessionEvent[] {
  const events: SessionEvent[] = []
  // The JSONL backend guarantees line 0 is the session header.
  for (let i = 1; i < lines.length; i++) {
-    const parsed: unknown = JSON.parse(lines[i] as string)
-    events.push(parsed as SessionEvent)
+    events.push(...decodeStorageRecord(JSON.parse(lines[i] as string)))
  }
  return events
 }
--- a/packages/support/llm-replay/tests/llm-replay.spec.ts
+++ b/packages/support/llm-replay/tests/llm-replay.spec.ts
@@ -90,6 +90,19 @@ describe('parseSessionLog', () => {
    const ev = chunkEvent(1, 1, 1, TEXT_CHUNKS[0] as StreamChunk)
    expect(parseSessionLog(`${header}\n\n${JSON.stringify(ev)}\n\n`)).toEqual([ev])
  })
+
+  it('expands a packed chunk row into its events (a fixture recorded with packChunks on)', () => {
+    const header = JSON.stringify({ type: 'session', version: 0, id: 's1', createdAt: 0 })
+    const row = JSON.stringify({
+      type: 'text-chunks', seq0: 1, time0: 0,
+      data: { turn: 1, step: 1, index: 0, dt: [0, 0], texts: ['a', 'b', 'c'] },
+    })
+    expect(parseSessionLog(`${header}\n${row}\n`)).toEqual([
+      chunkEvent(1, 1, 1, { type: 'text-delta', index: 0, text: 'a' }),
+      chunkEvent(2, 1, 1, { type: 'text-delta', index: 0, text: 'b' }),
+      chunkEvent(3, 1, 1, { type: 'text-delta', index: 0, text: 'c' }),
+    ])
+  })
 })

 describe('deriveReplayScript', () => {