feat(session-query): expose projectSessions batch projection

Public SessionQueryService.projectSessions wraps the existing corpus
projectMany: one persistence listing, bounded persisted-inspect
concurrency, per-id failure isolation, and a synchronous projector over
a borrowed source with no replay validation or cloning.
readTitleSnapshots now routes through it; LogicalSessionSource and
LogicalProjectionResult are exported and documented.

docs/core-data-structures/session-query.i18n.yaml

@@ -1,6 +1,6 @@
 # Bilingual-pair consistency record (docs/i18n/README.md): the git blob hash of each
 # 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
-session-query.md: d92af4bac34f7d41457e9e193111c3a53fe8022e
-session-query.zh.md: ecf330b0a361ffae352a91c0d35524444936606d
+#   pnpm run verify-translation-pairing --write docs/core-data-structures/session-query.md
+session-query.md: cffbd792e8cab6e79365ceb4e0b1d996e7e93cf5
+session-query.zh.md: 2b67761ec3bcd96ee9de15511ec44516f1fe525d

docs/core-data-structures/session-query.md

@@ -84,6 +84,25 @@ type SessionTitleObservationResult =
   }
 ```
 
+`projectSessions` batches arbitrary synchronous folds over the same live-preferred corpus: each `LogicalSessionSource` is a borrowed raw log — never replay-validated or cloned — that is valid only for the projector call, so a batch summary costs one bounded read per persisted session. Each `LogicalProjectionResult` settles per unique requested id under the same isolation and cancellation rules as batch title reads.
+
+```ts type-equiv
+/** Borrowed source visible only during one synchronous batch projection. */
+interface LogicalSessionSource {
+  /** Header selected with `events`; callers must clone retained output. */
+  readonly header: SessionHeader
+  /** Raw events selected with `header`; valid only for the projection call. */
+  readonly events: readonly SessionEvent[]
+}
+```
+
+```ts type-equiv
+/** One source-projection result in a batch logical-corpus observation. */
+type LogicalProjectionResult<Value> =
+  | { sessionId: SessionId; status: 'fulfilled'; value: Value }
+  | { sessionId: SessionId; status: 'rejected'; reason: unknown }
+```
+
 ```ts type-equiv
 /** Lightweight metadata for one event within a logical session. */
 interface SessionEventRecord {

docs/core-data-structures/session-query.zh.md

@@ -84,6 +84,25 @@ type SessionTitleObservationResult =
   }
 ```
 
+`projectSessions` 在同一实时优先语料库上批量执行任意同步折叠：每个 `LogicalSessionSource` 都是借用的原始日志——从不做回放验证，也从不克隆——仅在投影函数调用期间有效，因此一次批量摘要对每个持久化会话只需一次有界读取。每个 `LogicalProjectionResult` 按唯一请求 id 结算，其失败隔离与取消规则与批量标题读取一致。
+
+```ts type-equiv
+/** Borrowed source visible only during one synchronous batch projection. */
+interface LogicalSessionSource {
+  /** Header selected with `events`; callers must clone retained output. */
+  readonly header: SessionHeader
+  /** Raw events selected with `header`; valid only for the projection call. */
+  readonly events: readonly SessionEvent[]
+}
+```
+
+```ts type-equiv
+/** One source-projection result in a batch logical-corpus observation. */
+type LogicalProjectionResult<Value> =
+  | { sessionId: SessionId; status: 'fulfilled'; value: Value }
+  | { sessionId: SessionId; status: 'rejected'; reason: unknown }
+```
+
 ```ts type-equiv
 /** Lightweight metadata for one event within a logical session. */
 interface SessionEventRecord {