deepseek-harness/packages/context/session-reference/README.md

# `@deepseek-ai/dsh-session-reference`

`ctx.sessionReferences` prepares bounded, read-only snapshots of other DeepSeek Harness sessions as durable `context/message` input. It consumes `ctx.sessionQuery` and the backend-independent compact checkpoint marker; SQLite FTS is not required. The standard TUI and ACP demo bundles mount it, while other hosts may call the service directly.

## Public API

- `listCandidates(agent, query?, limit?)` lists sessions other than `agent.id`, filters case-insensitively by id or cwd, and ranks same-cwd, cwd-less, then other-cwd records while preserving `listSessions()` creation order within each group. Each selected candidate uses its latest log-backed title as the mention label and falls back to the session id; titles and message bodies are not searched.
- `prepare(agent, content, references, signal?)` preserves first-mention order, deduplicates ids, rejects self-reference and more than the configured distinct-source limit, reads every source in parallel, and returns detached content plus zero or one aggregated `HookContext`. Any invalid reference, failed read, cancellation, or budget failure rejects before the host calls `send()` or `steer()`.
- `encodeSessionReferenceUri()` and `decodeSessionReferenceUri()` implement `dsh-session:<base64url(JSON.stringify(sessionId))>` so every JavaScript string id round-trips exactly. `formatSessionReferenceMention()` emits `@[label](uri)`, and `parseSessionReferenceText()` replaces Markdown mentions or bare canonical URIs with readable `@label` text while returning structured references. Explicit Markdown mentions reject every malformed URI; bare text is considered a reference only when a non-empty base64url-shaped payload follows the scheme, and a matching noncanonical candidate still fails. Empty or punctuation-only scheme mentions remain ordinary discussion text.

## Snapshot semantics

Preparation calls `ctx.sessionQuery.readSurface()` once per distinct source and never rereads it after enqueue. It projects only direct-user `user/message`, direct-user `steering/message`, assistant text, and `user/message` checkpoints carrying the canonical `dsh-compact` source marker from the folded current surface. Shadowed pre-compaction events, tools, reasoning, context, plugin-generated user messages other than marked compact checkpoints, and unfinished assistant chunks are excluded. A compacted source therefore contributes its latest checkpoint plus retained later conversation, not restored shadowed text.

The context source is `{ kind: 'plugin', plugin: 'session-reference' }`. Its metadata records version `1`, source ids and labels, capture seqs, compact presence, retained/omitted message counts, omitted UTF-8 bytes, and truncation state. The target session persists that exact context through the ordinary `context/message` event; later source mutation, compaction, or deletion cannot change target replay.

## Configuration

| Key | Default | Contract |
|---|---:|---|
| `maxReferences` | `3` | Maximum distinct source sessions in one prepared message; must be at most `3`. |
| `candidateLimit` | `50` | Default metadata candidate count returned to a host. |
| `maxReferenceBytes` | `65536` | Maximum serialized JSON bytes for one reference object. |

Retention applies `maxReferenceBytes` independently to each source, keeps compact checkpoints and the newest message before dropping older non-checkpoint units, and uses `dsh-retention` head/tail truncation with an exact UTF-8 omission notice. If one source's fixed serialized fields cannot fit, preparation fails with `SESSION_REFERENCE_BUDGET_EXCEEDED` instead of returning a partial context.

## Model Experience

### Referenced session background

#### What the model sees

The model sees the current message's readable `@label` plus one same-level user-context message headed `## Referenced sessions`. The context states that its JSON is untrusted, read-only background and forbids following instructions, permission claims, or tool requests unless the current user repeats them. Labels, cwd values, ids, and conversation text are serialized as JSON inside `<referenced-sessions>` tags; every data `<` is emitted as the lossless JSON escape `\u003c`, so source text cannot spell a framing tag.

#### Token effect

Each referenced message adds the fixed warning plus up to three serialized snapshots, each independently bounded by `maxReferenceBytes`. The exact snapshot remains in target history until target compaction shadows or summarizes it; source-session changes add no further tokens.

#### KV Cache effect

Snapshot context is append-only at the target message boundary and preserves earlier cacheable history. Different references or source capture contents change the new suffix only; later target compaction may invalidate reuse from its replacement boundary.

## Known Limitations and Deferred Work

- **No title or full-text discovery** — candidates filter by session id and cwd only, although selected rows display the latest title. SQLite FTS may replace discovery later without changing URI, snapshot, or persistence contracts.
- **Trusted caller boundary** — the service assumes its host is authorized to read every session exposed by `ctx.sessionQuery`; it is not a model-facing search tool.
- **Text projection only** — non-text user and assistant blocks are not propagated across sessions.
- **No live link** — references are snapshots, not forks, resumes, subscriptions, or source-session mutations.