feat(session-query): add SQLite full-text search

docs/rfc/implemented/feature/2026-07-10-session-query-service.md

@@ -6,11 +6,11 @@ Status: implemented
 
 Session history exists in two places: current `SessionStore` objects and an optional persistence backend. Consumers that need exact inspection would otherwise duplicate live-versus-persisted precedence, persistence lifecycle handling, raw-event surface classification, and defensive cloning. Durable state can lag the live log between checkpoints, so persistence alone is not a truthful current source.
 
-Full-text search is related but materially larger. Designing provider registration, extraction, synchronization, invalidation, ranking, and cursor contracts before a real backend exists creates two speculative state machines: one in the interface service and another in the eventual database package.
+Full-text search is related but materially larger. Putting provider coordination, synchronization, invalidation, ranking, and cursor state into the exact-read service would create a second state machine beside the concrete database owner.
 
 ## Decision
 
-`@deepseek-ai/dsh-session-query` owns `ctx.sessionQuery`, a small trusted exact-read service over one logical corpus. It exposes `listSessions()`, `listEvents(sessionId)`, and bounded `readEvent(request)`. It does not expose filters, lineage or provenance traversals, text extractors, search requests, provider registration, or derived-index synchronization.
+`@deepseek-ai/dsh-session-query` owns `ctx.sessionQuery`, a small trusted exact-read service over one logical corpus. It exposes `listSessions()`, `listEvents(sessionId)`, provider-independent `filterEvents(sessionId, filters)`, and bounded `readEvent(request)`. The package also declares the separate abstract `ctx.sessionSearch` contract and shared semantic extraction used by the [SQLite search decision](2026-07-10-sqlite-session-query-provider.md), but `ctx.sessionQuery` does not coordinate providers or synchronize a derived index.
 
 The service observes the optional `ctx.sessionPersistence` binding dynamically but retains no persisted cache or invalidation listener. Each cross-corpus list asks the active backend for authoritative metadata, then overlays a fresh live-store list. Matching ids become one `SessionRecord`: the live header wins and `live`/`persisted` independently report source availability. Immutable header disagreement is `SESSION_QUERY_SOURCE_CONFLICT`.
 
@@ -31,11 +31,11 @@ The service is context-wide trusted infrastructure, not an authorization layer.
 - **Put logical-corpus resolution directly in every consumer** — rejected because source precedence, conflicts, optional-service lifecycle, cloning, and surface classification are shared correctness rules.
 - **Query only persistence** — rejected because checkpoints can lag the current live log.
 - **Cache persisted metadata and listen for writes/removals** — rejected because exact reads can ask the authoritative sources directly, while cache invalidation adds lifecycle and concurrency state before scale requires it.
-- **Define a provider-neutral search protocol now** — rejected because no provider consumes it. The first SQLite FTS package should own one reconciliation/transaction state machine; a smaller shared seam can be extracted later only when a second implementation proves the boundary.
-- **Include lineage, provenance, and generic filters in phase one** — rejected because no current consumer requires them and canonical logs remain sufficient to add them with evidence later.
+- **Put provider registration into the exact-read service** — rejected because the SQLite package owns one reconciliation/transaction lifecycle; a registry would split that state without a second provider to justify it.
+- **Include lineage and provenance traversal** — rejected because canonical logs remain sufficient to add those higher-level views when a concrete consumer requires them.
 
 ## Consequences
 
-Phase one has one source-resolution state variable: the currently mounted persistence service. There are no provider queues, fingerprints, extractor registries, observation generations, or derived index updates. Exact reads remain usable in live-only deployments and deterministic when persistence is present.
+Exact reads have one source-resolution state variable: the currently mounted persistence service. There are no provider queues, fingerprints, extractor registries, observation generations, or derived index updates in `ctx.sessionQuery`. Exact reads and semantic scans remain usable in live-only deployments and deterministic when persistence is present.
 
-Cross-corpus listing and persisted exact reads perform backend I/O on each call. That is deliberate: correctness comes from current authoritative state, and scale-oriented search belongs to the phase-two database. Full-text search is unavailable until that package defines and implements its complete contract.
+Cross-corpus listing and persisted exact reads perform backend I/O on each call. That is deliberate: correctness comes from current authoritative state, while scale-oriented full-text search uses the separately owned SQLite derived index.

docs/rfc/implemented/feature/2026-07-10-sqlite-session-query-provider.md

@@ -0,0 +1,57 @@
+# RFC: SQLite FTS5 session search
+
+Status: implemented
+
+## Problem
+
+The exact-read `ctx.sessionQuery` service deliberately has no derived index. Large persisted histories need full-text search without scanning every event on every query, while current live sessions need an overlay newer than the last durability checkpoint. Search also needs concrete ranking, snippets, filters, pagination, cancellation, and rebuild behavior.
+
+Splitting those concerns across a provider coordinator and a database implementation would create two coupled reconciliation state machines. The first implementation needs to own source observation, extraction, SQLite transactions, generations, and query execution as one lifecycle while still exposing a small provider-neutral call contract.
+
+## Decision
+
+`@deepseek-ai/dsh-session-query` declares an independent abstract `ctx.sessionSearch` service without changing the exact-read `ctx.sessionQuery` key. `searchSessions(request, exec?)` returns cursor-paginated `SessionSearchHit`s grouped by each session's strongest matching event; `searchEvents(request, exec?)` returns `SessionEventSearchHit`s within one logical session. Both requests require `query`, accept `limit` and an opaque `cursor`, and support an optional abort signal. Session search accepts `sessionFilters` plus event metadata filters; event search accepts event metadata filters. Results expose bounded plain-text snippets but no provider identifier or numeric relevance score.
+
+`@deepseek-ai/dsh-session-query-sqlite` is the sole concrete owner of `ctx.sessionSearch`. It depends on live `ctx.sessions`, observes optional `ctx.sessionPersistence` dynamically, and owns a dedicated derived SQLite database. There is no search-provider registry, coordinator, persistence event, or agent-loop integration.
+
+The interface package also owns shared first-party semantic extraction and provider-independent filtering. `SessionResultFilter` covers id, nullable cwd, created-at range, nullable parent, and availability. `SessionEventResultFilter` covers seq/time ranges, event type, surface, and literal semantic text. Arrays are ANDed and list values are ORed. The text clause escapes caller input into a Unicode case-insensitive regular expression whose whitespace runs match one or more whitespace characters; it is available through `ctx.sessionQuery.filterEvents()` and is not delegated to an FTS provider.
+
+## Search semantics
+
+Each semantic event is one FTS document carrying session metadata, event metadata, surface classification, and extracted text. All `current`, `shadowed`, and `log-only` documents participate unless a surface filter narrows them. Metadata filters compile to parameterized SQL before ranking. Session results partition matching documents by session and retain the strongest one.
+
+Ordering is deterministic: BM25 ascending, event time descending, session id ascending for the cross-session scope, and seq descending. Provider scores remain private. Snippets normalize whitespace and are bounded by Unicode code points. Opaque cursors bind to the service instance, scope, canonical normalized request, offset, and relevant generation. Any corpus change invalidates cross-session cursors; a within-session cursor changes only when its target source/generation changes, so unrelated sessions do not invalidate it. Reopening creates a new service instance and invalidates old cursors.
+
+Queries are trimmed, whitespace-normalized, and quoted as one literal FTS5 phrase. Embedded quotes are doubled before binding, so MATCH operators such as `OR`, `NEAR`, quotes, parentheses, and `*` remain data rather than executable query syntax. Phrase matching follows tokenizer tokens rather than arbitrary substrings.
+
+## Tokenizer choice
+
+Both persistent and live FTS5 tables use `unicode61`. The implementation experiment found that this tokenizer supports the two-character token `AI` and produces an index about 2.1× smaller than the trigram alternative. The accepted limitation is token/phrase recall: `AI` does not match the larger token `BRAID`, and arbitrary substring search uses the provider-independent text scan instead.
+
+## Extraction and reconciliation
+
+The shared extractor includes message text, reasoning, nested tool-call/result content, tool names and arguments, blocked-prompt reasons, todo status/content, and error or terminal status detail. Structural boundaries, stream chunks, request headers, successful completion markers, and unknown declaration-merged event/content variants produce no document. Surface classification reuses `foldSurface()` so search agrees with model-history derivation.
+
+One serialized operation observes complete persisted and live sources, computes stable fingerprints, reconciles rows in one transaction, and executes the query. Unchanged persisted sessions retain their rows and generation. New, changed, and deleted persisted sessions update on the next search. A source or extraction failure cannot mark a row current, and a transaction failure rolls back so a later search retries.
+
+Persisted documents survive restarts. Live sessions use connection-local TEMP tables, shadow the persisted base for the same id, and reveal that base on detach. Closing the database drops live rows. Unmounting persistence hides durable rows without treating absence as authoritative deletion; remounting observes and reconciles the backend again. Conflicting immutable live and durable headers fail rather than combining sources.
+
+The derived schema has its own application id and monotonic schema version. A recognized incompatible version resets only this derived database. A database with a foreign application id or unrecognized user tables is refused, which prevents an accidentally configured canonical session database from being reset.
+
+Cancellation rejects queued operations and caller waits around asynchronous source observation without committing an aborted observation. Node's synchronous `DatabaseSync` MATCH call cannot be interrupted once it is executing on the JavaScript thread, so the service checks the signal at serialized boundaries but does not promise mid-statement preemption.
+
+## Alternatives considered
+
+- **Add FTS tables to the canonical persistence database** — rejected because a rebuildable index must not share the authoritative log's schema, reset, or failure boundary.
+- **Add a phase-one provider registry and coordinator** — rejected because one implementation provides no evidence for registration semantics and would split one reconciliation lifecycle across two owners.
+- **Persist live overrides immediately** — rejected because live events are not canonical until the existing checkpoint commits.
+- **Use the FTS5 trigram tokenizer** — rejected because it omits useful queries shorter than three characters and measured about 2.1× the index size of `unicode61`; literal substring filtering remains available through the scan path.
+- **Return BM25 scores** — rejected because provider-specific numeric scales are unstable across corpus changes.
+
+## Consequences
+
+Search has a small provider-neutral API while its only backend owns every derived-index state transition. The separate database adds configuration and a reconciliation read before queries, but index corruption, reset, and tokenizer changes cannot endanger canonical logs. Persistent fingerprints avoid rewriting unchanged sessions; TEMP live overlays preserve current-session truth without making uncheckpointed events durable.
+
+The chosen tokenizer supports short tokens with a smaller index but does not promise substring recall. Literal phrases make query syntax safe and predictable at the cost of excluding boolean/full MATCH expressions. Cancellation is effective while queued or awaiting sources, but synchronous SQLite execution remains a non-preemptible section.
+
+Unit coverage pins extraction, filters, both search scopes, all default surfaces, metadata-before-ranking, snippets, literal escaping, deterministic ties, complete pagination, scoped cursor invalidation, dynamic persistence mount/unmount, restart reconciliation, live shadow/reveal/reopen, schema safety, rollback retry, and queued/in-flight source-wait cancellation. A keyless real-Loader-path test combines the package with the real SQLite persistence backend.