refactor(session): fold the session family into packages/session/

git mv the 12 packages from session-persistence/, session-projection/,
session-title/, and telemetry/ into one session/ group per the
regrouping RFC; merge the four group READMEs into one bilingual
triplet; rewrite the group segment in tsconfig references (intra-group
references shorten to ../<pkg>), tsconfig.base.json paths/globs,
knip.json keys, vitest include, gate scripts, and authored doc/note
citations; regenerate module graph, doc graphs, catalogs, and the
lockfile importer keys. No npm names change.

Full unit suite: 8779 passed; the 18 reported failures reproduce as
env flakes (ambient-proxy IPv6 tunneling, watched-dir inotify
timeouts under parallel load) — each passes in isolation with
NO_PROXY set, matching their known pre-existing behavior on master.

packages/session/session-title/README.md

@@ -0,0 +1,55 @@
+# @deepseek-ai/dsh-session-title
+
+English | [中文](README.zh.md)
+
+Log-backed session titles with an immediate deterministic fallback and one optional asynchronous provider. Every accepted revision is a log-only `session/title` event; `foldSessionTitle()` and `ctx.sessionTitle.get()` select the latest event and return its event seq and timestamp.
+
+Only text blocks from human `user/message` events are eligible. The first eligible prompt schedules a fallback from its first words within the configured UTF-8 byte limit. Whitespace is normalized, terminal control sequences are removed, and truncation never splits a code point. Empty and non-text prompts wait for later eligible input.
+
+## Service: `SessionTitleService` (ctx key: `sessionTitle`)
+
+- `get(session)` folds the latest accepted title from a live or replayed log.
+- `refresh(session, signal?)` materializes the fallback when needed, then explicitly runs the registered provider over the current eligible messages. Provider errors and caller cancellation reject; cancellation does not roll back an already accepted fallback event.
+- `rename(session, title)` accepts an explicit user title synchronously: it normalizes the text, supersedes in-flight automatic work, and appends a `session/title` event with the `user` source. A user-sourced latest title pins the session — later user messages schedule no automatic revision; an explicit `refresh` remains the deliberate unpin.
+- `register(provider)` installs the sole optional provider and returns its awaitable Cordis effect disposer. A second registration throws immediately; disposal aborts pending and active calls, waits for their settlement, and only then permits another provider to register.
+
+Automatic work never delays the main agent response. A provider starts only after a marked loop-built request's exact route matches the current logged `request/header`, including when the unchanged header needs no new snapshot. Its late completion appends a standalone log-only event directly through `Session` without opening a turn. Persistence observes that event eagerly and drains on ordinary lifecycle checkpoints; title publication itself does not force a flush. Automatic failures warn and retain the latest title. New all-message revisions, provider disposal, session disposal, and explicit refresh abort older work, and a stale completion cannot append. Concurrent explicit refreshes reserve their revision before provider work, while overlapping automatic and explicit fallback requests share one session-local in-flight append. The service and bundled model provider each append their own literal event type, so no generic title-write marker, cast, or settlement queue is needed. Service teardown cancels queued work and drains calls that ignore cancellation before unloading completes.
+
+Forks inherit title events in their seed unchanged. The first-message cadence does not automatically retitle a child; the all-messages cadence may append a new revision after the child receives a later human prompt.
+
+## Configuration
+
+All limits are required; the library supplies no defaults.
+
+| Key | Contract |
+|---|---|
+| `fallbackMaxWords` | Positive maximum whitespace-delimited words in the deterministic fallback. |
+| `fallbackMaxBytes` | Positive maximum UTF-8 bytes in the fallback; must not exceed `maxTitleBytes`. |
+| `maxTitleBytes` | Positive maximum UTF-8 bytes accepted from any source. |
+
+## Provider contract
+
+A provider supplies a branded stable id, automatic mode (`first-message` or `all-user-messages`), and `generate(request)`. The request carries the live session, all eligible messages through one fixed revision, the current logged main-request route when available, and cancellation. The result identifies a non-empty title, unique ordered source-message seqs from that request, and optional model provenance. The service normalizes and validates the result before it becomes durable.
+
+See the [session-title data structures](../../../docs/core-data-structures/session-title.md) and [implemented decision](../../../.agents/notes/implemented/feature/2026-07-21-log-backed-session-titles.md).
+
+## Model Experience
+
+### Session title state
+
+#### What the model sees
+
+Nothing. `session/title` is log-only and never enters the session surface, `deriveMessages()`, system prompt, tool schemas, or request prefix.
+
+#### Token effect
+
+The fallback and accepted provider revisions add zero tokens to the main agent request. An optional provider's separate auxiliary request is documented by that provider package.
+
+#### KV Cache effect
+
+None for the main request; title events do not change its reconstructed content or cache key.
+
+## Known Limitations and Deferred Work
+
+- Title deletion (unpinning back to automatic titles without an explicit `refresh`), search, and list indexing are outside this service.
+- The provider registry deliberately accepts at most one implementation, so a deployment cannot compose competing title strategies without writing one provider that owns their precedence.