fix(scripts): complete fixture migration diagnostics

.agents/notes/implemented/architecture/2026-07-26-packed-chunk-rows-by-default.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write
-2026-07-26-packed-chunk-rows-by-default.md: e1090264238ff15670a58ee33b062ad340241b8e
-2026-07-26-packed-chunk-rows-by-default.zh.md: b193e37987946764d6c19583f2e3f195ae31bf61
+2026-07-26-packed-chunk-rows-by-default.md: d6a044676604e4a4512a7a6674edb80e120b2f3c
+2026-07-26-packed-chunk-rows-by-default.zh.md: 184d462d70dcc666a0b38497ead307ce6861382d

.agents/notes/implemented/architecture/2026-07-26-packed-chunk-rows-by-default.md

@@ -34,7 +34,7 @@ Focused package tests keep unpacked and mixed-layout inputs for reader compatibi
 
 The temporary [`scripts/migrate-packed-session-fixtures.ts`](../../../../scripts/migrate-packed-session-fixtures.ts) command lets in-flight branches converge after merging current `master`: `pnpm run migrate:packed-session-fixtures` discovers the same repository-wide fixture set as the permanent gate, preserves each header line, decodes existing mixed records, writes the canonical packed body, proves decoded equality, and proves idempotence. It never calls a model or regenerates transcript and presentation outputs.
 
-The command remains linked from the testing policy and ACP snapshot README while older branches may carry fixture edits. The [removal proposal](../../proposed/process/2026-07-26-remove-packed-session-fixture-migrator.md) deletes the CLI, package command, this transitional section, and the documentation links once a live open-PR inventory shows that every affected branch is merged, closed, or canonical. The shared canonicalizer and snapshot gate remain permanent.
+The command remains linked from the testing policy and ACP snapshot README while older branches may carry fixture edits. The [removal proposal](../../proposed/process/2026-07-26-remove-packed-session-fixture-migrator.md) deletes the CLI, package command, this transitional section, and the documentation links, then replaces the permanent gate's command-specific remediation text once a live open-PR inventory shows that every affected branch is merged, closed, or canonical. The shared canonicalizer and snapshot gate remain permanent.
 
 ### Verification contract
 

.agents/notes/implemented/architecture/2026-07-26-packed-chunk-rows-by-default.zh.md

@@ -34,7 +34,7 @@ ACP 和 headless 快照运行会采集默认 JSONL 后端的输出。TUI 和 web
 
 临时命令 [`scripts/migrate-packed-session-fixtures.ts`](../../../../scripts/migrate-packed-session-fixtures.ts) 让在途分支合并当前 `master` 后可以完成收敛：`pnpm run migrate:packed-session-fixtures` 会发现与永久门禁相同的仓库级 fixture 集合，保留各文件的 header 行，解码现有混合记录，写入规范打包正文，并证明解码结果相等且操作具有幂等性。该命令绝不会调用模型，也不会重新生成 transcript（文本记录）与呈现输出。
 
-只要较旧分支仍可能携带 fixture 改动，测试政策和 ACP 快照 README 就会继续链接该命令。最新的开放 PR（Pull Request）清单确认每个受影响分支均已合并、关闭或符合规范后，[移除提案](../../proposed/process/2026-07-26-remove-packed-session-fixture-migrator.md)会删除该 CLI、包命令、本过渡章节和文档链接。共享规范布局转换器与快照门禁保持永久存在。
+只要较旧分支仍可能携带 fixture 改动，测试政策和 ACP 快照 README 就会继续链接该命令。最新的开放 PR（Pull Request）清单确认每个受影响分支均已合并、关闭或符合规范后，[移除提案](../../proposed/process/2026-07-26-remove-packed-session-fixture-migrator.md)会删除该 CLI、包命令、本过渡章节和文档链接，并替换永久门禁中仅适用于该命令的修复指引。共享规范布局转换器与快照门禁保持永久存在。
 
 ### 验证契约
 

.agents/notes/proposed/process/2026-07-26-remove-packed-session-fixture-migrator.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write
-2026-07-26-remove-packed-session-fixture-migrator.md: d5f8ff65a38618c5f321f096921f7ce2b8af2d75
-2026-07-26-remove-packed-session-fixture-migrator.zh.md: d46e9e035709c26f59cb7f0a6908e38d0da08bbe
+2026-07-26-remove-packed-session-fixture-migrator.md: 0a29ef98828ac07d291392d637b0508937c9a9a6
+2026-07-26-remove-packed-session-fixture-migrator.zh.md: 64b994855a7e92d5b0922884b6c66df1b82b6d90

.agents/notes/proposed/process/2026-07-26-remove-packed-session-fixture-migrator.md

@@ -12,7 +12,7 @@ Once every such branch is merged, closed, or already canonical, the write comman
 
 ## Proposal
 
-Remove the temporary `scripts/migrate-packed-session-fixtures.ts` CLI and the root `migrate:packed-session-fixtures` package command after a live inventory confirms that no open pull request still needs to convert session-format JSONL. Remove the transitional command links from the testing policy, the ACP snapshot README, and the implemented packed-row Agent Note in the same change.
+Remove the temporary `scripts/migrate-packed-session-fixtures.ts` CLI and the root `migrate:packed-session-fixtures` package command after a live inventory confirms that no open pull request still needs to convert session-format JSONL. Remove the transitional command links from the testing policy, the ACP snapshot README, and the implemented packed-row Agent Note in the same change; replace the command-specific remediation text in `scripts/session-fixture-layout.snapshot.ts` with command-independent canonical-layout guidance.
 
 Retain `scripts/session-fixture-layout.ts`, its unit tests, and `scripts/session-fixture-layout.snapshot.ts`. They define and enforce the permanent canonical layout; only the branch-facing writer is temporary.
 
@@ -29,7 +29,7 @@ Before removing the command, each affected branch merges the current `master`, r
 ## Acceptance criteria
 
 - A live open-PR inventory finds no branch with session-format JSONL changes that still depends on the temporary migration command.
-- The temporary CLI, root package command, and every branch-convergence link are absent; the permanent canonicalizer, unit tests, and snapshot check remain.
+- The temporary CLI, root package command, every branch-convergence link, and the command-specific gate diagnostic are absent; the permanent canonicalizer, unit tests, and snapshot check remain.
 - `pnpm run test:snapshot`, `pnpm run doc-sync`, lint, and whitespace validation pass without the temporary command.
 - Current documentation describes only the packed default and permanent canonical-layout enforcement.
 

.agents/notes/proposed/process/2026-07-26-remove-packed-session-fixture-migrator.zh.md

@@ -12,7 +12,7 @@ Status: proposed
 
 ## 提案
 
-最新清单确认不再有任何开放 PR（Pull Request）需要转换会话格式 JSONL 后，移除临时 CLI `scripts/migrate-packed-session-fixtures.ts`，以及根包（package）提供的 `migrate:packed-session-fixtures` 命令。在同一变更中，移除测试政策、ACP 快照 README 和已实现打包行 Agent Note（agent 决策记录）中指向该过渡命令的链接。
+最新清单确认不再有任何开放 PR（Pull Request）需要转换会话格式 JSONL 后，移除临时 CLI `scripts/migrate-packed-session-fixtures.ts`，以及根包（package）提供的 `migrate:packed-session-fixtures` 命令。在同一变更中，移除测试政策、ACP 快照 README 和已实现打包行 Agent Note（agent 决策记录）中指向该过渡命令的链接，并将 `scripts/session-fixture-layout.snapshot.ts` 中仅适用于该命令的修复指引替换为与具体命令无关的规范布局指引。
 
 保留 `scripts/session-fixture-layout.ts`、其单元测试和 `scripts/session-fixture-layout.snapshot.ts`。它们定义并强制执行永久规范布局；只有面向分支的写入器是临时机制。
 
@@ -29,7 +29,7 @@ Status: proposed
 ## 验收标准
 
 - 最新开放 PR 清单未发现任何仍依赖临时迁移命令处理会话格式 JSONL 改动的分支。
-- 临时 CLI、根包命令与所有分支收敛链接均不存在；永久规范布局转换器、单元测试和快照检查仍然保留。
+- 临时 CLI、根包命令、所有分支收敛链接与仅适用于该命令的门禁诊断均不存在；永久规范布局转换器、单元测试和快照检查仍然保留。
 - `pnpm run test:snapshot`、`pnpm run doc-sync`、lint 和空白校验在没有临时命令的情况下通过。
 - 当前文档仅描述打包默认值和永久规范布局强制机制。
 

scripts/session-fixture-layout.spec.ts

@@ -49,4 +49,9 @@ describe('canonicalSessionFixture', () => {
     expect(() => canonicalSessionFixture(`${HEADER}\n{not-json}\n`, 'broken.jsonl'))
       .toThrow(/broken\.jsonl:2: invalid JSON/)
   })
+
+  it('labels malformed packed rows with the fixture path and line', () => {
+    expect(() => canonicalSessionFixture(`${HEADER}\n{"type":"text-chunks"}\n`, 'broken.jsonl'))
+      .toThrow(/broken\.jsonl:2: invalid session storage record: malformed text-chunks storage row/)
+  })
 })

scripts/session-fixture-layout.ts

@@ -41,7 +41,15 @@ function isSessionHeader(value: unknown): boolean {
 }
 
 function decodeBody(lines: readonly RecordLine[], label: string): SessionEvent[] {
-  return lines.flatMap(line => decodeStorageRecord(parseRecord(line, label)))
+  return lines.flatMap((line) => {
+    const record = parseRecord(line, label)
+    try {
+      return decodeStorageRecord(record)
+    } catch (error) {
+      const detail = error instanceof Error ? error.message : String(error)
+      throw new Error(`${label}:${line.line}: invalid session storage record: ${detail}`, { cause: error })
+    }
+  })
 }
 
 function renderFixture(headerLine: string, events: readonly SessionEvent[]): string {