Merge remote-tracking branch 'origin/master' into jsonl-packed-chunk-rows

Conflicts: the four generated catalog docs (regenerated over merged sources),
session index.ts exports (keep chunk-rows exports + master's SessionSurface
re-export), stdio/acp demo config schema and persistence wiring (thread
packChunks through master's DEFAULT_PERSISTENCE_ROOT/UI shape), stdio README
config table, and the jsonl spec import line. The packed-chunk fixture also
gains the provenance field master made required on assistant/message.

packages/session-persistence/README.md

@@ -8,4 +8,4 @@ The durable session-persistence seam and its storage backends. The interface pac
 | `session-persistence-jsonl/` | JSONL-sidecar persistence backend | (registers `ctx.sessionPersistence`) |
 | `session-persistence-sqlite/` | SQLite persistence backend | (registers `ctx.sessionPersistence`) |
 
-The interface lives at `session-persistence/session-persistence/`; backends are flat siblings. A new storage backend joins here and registers on `ctx.sessionPersistence`. See [session persistence](../../docs/rfc/implemented/architecture/2026-06-14-session-persistence.md).
+The interface lives at `session-persistence/session-persistence/`; backends are flat siblings. A new storage backend joins here and registers on `ctx.sessionPersistence`. See [session persistence](../../.agents/notes/implemented/architecture/2026-06-14-session-persistence.md).

packages/session-persistence/session-persistence-jsonl/README.md

@@ -21,11 +21,13 @@ The JSONL durable session-persistence backend — a concrete `SessionPersistence
 | `root` | `string` (required) | Root directory for all session files. **No default** — a `process.cwd()` default would scatter files as the process's cwd changes (bash calls, subprocesses). |
 | `packChunks` | `boolean` (default `false`) | Write delta-chunk runs as packed rows (~60% smaller logs measured on a real coding session). Off, the written layout is byte-identical to the pre-packing format; reading packed rows works regardless of this switch. Off by default while the snapshot goldens stay one-event-per-line — recording with packing on rewrites every fixture `session.jsonl`. |
 
+`locate(meta)` returns `{ kind: 'jsonl', path }` using the resolved absolute root and the same cwd-bucket/id encoding as materialization. It performs no filesystem I/O: the target can be returned before the file exists, and an existing file contains only the last flushed prefix.
+
 ## Durability and crash semantics
 
-- **Lazy materialization.** `create(meta)` writes nothing; on the first `append`, the backend writes and `fsync`s a temporary file, publishes it without overwrite via a hard link, then `fsync`s the directory. A created-but-never-appended session leaves nothing on disk and is absent from `list`.
+- **Lazy materialization.** `create(meta)` writes nothing; on the first `append`, the backend writes and `fsync`s a temporary file, publishes it without overwrite via a hard link, then `fsync`s the directory when the host supports it. A created-but-never-appended session leaves nothing on disk and is absent from `list`.
 - **Append-only.** Committed events (at or below a flushed `turn/end`) are never rewritten. Subsequent appends are line appends at EOF + `fsync`.
-- **Crash recovery — preserve valid tail work.** `load` keeps the contiguous valid prefix of an interrupted final turn. It truncates from the first unparsable or sequence-gapped uncommitted record, then appends the synthetic tool, step, and turn closers required by the shared [persistence contract](../../../docs/rfc/implemented/architecture/2026-06-14-session-persistence.md); the same defect at or before the last committed `turn/end` rejects.
+- **Crash recovery — preserve valid tail work.** `load` keeps the contiguous valid prefix of an interrupted final turn. It truncates from the first unparsable or sequence-gapped uncommitted record, then appends the synthetic tool, step, and turn closers required by the shared [persistence contract](../../../.agents/notes/implemented/architecture/2026-06-14-session-persistence.md); the same defect at or before the last committed `turn/end` rejects.
 - **Contiguous-seq.** `append` rejects a batch whose first `seq` does not continue the stored log, and rejects non-JSON-serializable `event.data` naming the offending event type.
 
 ## Write path
@@ -36,9 +38,17 @@ The plugin buffers frozen session events and drains them on flush or disposal. A
 
 ### Resumed conversation history
 
-**What the model sees**: JSONL storage contributes no live prompt or schema. Loading restores stored surface history and preserves prior request headers for reconstruction; the new loop composes its current envelope. Each unanswered call in an interrupted tail is balanced with the exact error text `Tool call interrupted by a crash; no result was recorded.` Raw `assistant/chunk` records do not duplicate messages.
+#### What the model sees
 
-**Token effect**: Zero live-request tokens. A resumed agent pays for retained history and its current envelope, plus the quoted repair result for each interrupted call.
+JSONL storage contributes no live prompt or schema. Loading restores stored surface history and preserves prior request headers for reconstruction; the new loop composes its current envelope. Each unanswered call in an interrupted tail is balanced with the exact error text `Tool call interrupted by a crash; no result was recorded.` Raw `assistant/chunk` records do not duplicate messages.
+
+#### Token effect
+
+Zero live-request tokens. A resumed agent pays for retained history and its current envelope, plus the quoted repair result for each interrupted call.
+
+#### KV Cache effect
+
+JSONL storage does not mutate live request prefixes. A resumed loop can reuse provider cache only when its reconstructed history, current envelope, and model route match; crash-repair results append.
 
 ## Known Limitations and Deferred Work
 
@@ -46,3 +56,4 @@ The plugin buffers frozen session events and drains them on flush or disposal. A
 - **Nothing deletes session files** — logs accumulate under `root` until removed externally (the seam has no deletion surface).
 - **Single-process assumption** — per-session serialization and the write cursor live in this process; two processes appending to the same `root` are not coordinated.
 - **Initial materialization requires hard-link support** — first append uses `link()` so same-id races fail instead of overwriting a committed log; a filesystem that cannot create hard links cannot host this backend.
+- **Windows cannot `fsync` directory handles through Node** — the backend tolerates only Windows `EPERM` from directory `fsync`; file-content `fsync` remains mandatory, but a crash can lose a newly published directory entry on a host without an equivalent directory-sync primitive.

packages/session-persistence/session-persistence-jsonl/src/index.ts

@@ -1,7 +1,8 @@
 /**
  * JSONL durable session-persistence backend. It stores a header and contiguous
  * events in one append-only file per session, and delegates orchestration to
- * {@link PersistenceCoordinator}.
+ * {@link PersistenceCoordinator}. Its side-effect-free locator returns the
+ * absolute per-session log target before materialization.
  * @module @deepseek-ai/dsh-session-persistence-jsonl
  */
 
@@ -12,7 +13,7 @@ import { dirname, resolve } from 'node:path'
 import { randomBytes } from 'node:crypto'
 import {
   SessionPersistence, PersistenceCoordinator,
-  type PersistenceBackend, type StoredPrefix,
+  type PersistenceBackend, type SessionLocation, type StoredPrefix,
 } from '@deepseek-ai/dsh-session-persistence'
 import type { SessionEvent, SessionId, SessionHeader } from '@deepseek-ai/dsh-session'
 import {
@@ -67,6 +68,9 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
   private packChunks: boolean
   private coordinator: PersistenceCoordinator<number>
 
+  /** Runtime host platform used to decide whether directory sync is supported. */
+  readonly internals: { platform: NodeJS.Platform } = { platform: process.platform }
+
   constructor(ctx: Context, public config: Config) {
     super(ctx)
     // Resolve once so later process.cwd() changes cannot split one backend across roots.
@@ -82,6 +86,11 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
   /* jscpd:ignore-start */
   // --- SessionPersistence service surface (delegated to the coordinator) ---
 
+  /** Resolve the absolute target path without touching the filesystem. */
+  locate(meta: SessionHeader): SessionLocation {
+    return { kind: 'jsonl', path: logPath(this.root, meta.cwd, meta.id) }
+  }
+
   create(meta: SessionHeader): Promise<void> {
     return this.coordinator.create(meta)
   }
@@ -216,11 +225,18 @@ export class SessionPersistenceJsonl extends SessionPersistence implements Persi
     }
   }
 
-  /** fsync a directory so a just-created or published entry inside it is crash-durable. */
+  /** fsync a directory when the host exposes that durability primitive. */
   private async syncDir(dir: string): Promise<void> {
     const handle = await open(dir, 'r')
     try {
-      await handle.sync()
+      try {
+        await handle.sync()
+      } catch (error: unknown) {
+        const code = (error as NodeJS.ErrnoException | null)?.code
+        // Node opens directories on Windows but its fsync binding rejects them.
+        // File-content fsync remains mandatory; only this unsupported primitive is skipped.
+        if (this.internals.platform !== 'win32' || code !== 'EPERM') throw error
+      }
     } finally {
       await handle.close()
     }

packages/session-persistence/session-persistence-jsonl/tests/jsonl.spec.ts

@@ -1,12 +1,13 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
 import { Context } from 'cordis'
-import { appendFile, mkdtemp, mkdir, rm, readFile, writeFile, readdir, stat } from 'node:fs/promises'
+import { appendFile, mkdtemp, mkdir, open, rm, readFile, writeFile, readdir, stat } from 'node:fs/promises'
+import type { FileHandle } from 'node:fs/promises'
 import { tmpdir } from 'node:os'
-import { join } from 'node:path'
+import { isAbsolute, join, relative, resolve } from 'node:path'
 import SessionStore, { SessionId } from '@deepseek-ai/dsh-session'
 import type { Session, SessionEvent, SessionHeader } from '@deepseek-ai/dsh-session'
 import SessionPersistenceJsonl from '@deepseek-ai/dsh-session-persistence-jsonl'
-import { encodeSegment, eventLines, logPath, scanLog, sessionDir } from '../src/format.ts'
+import { encodeSegment, eventLines, logPath, scanLog, sessionDir, toHeaderLine } from '../src/format.ts'
 import { runPersistenceContract, meta, oneTurnLog, appendLog } from '../../session-persistence/tests/contract.ts'
 import { runCoordinatorContract, type CoordinatorFixture } from '../../session-persistence/tests/coordinator-contract.ts'
 
@@ -40,9 +41,25 @@ async function freshRoot(): Promise<string> {
 }
 
 afterEach(async () => {
+  vi.restoreAllMocks()
   for (const d of dirs.splice(0)) await rm(d, { recursive: true, force: true })
 })
 
+async function rejectDirectorySync(code: string): Promise<void> {
+  const handle = await open(root, 'r')
+  const proto = Object.getPrototypeOf(handle) as { sync: () => Promise<void> }
+  await handle.close()
+  const realSync = proto.sync
+  vi.spyOn(proto, 'sync').mockImplementation(async function (this: FileHandle) {
+    if ((await this.stat()).isDirectory()) {
+      const error = new Error(`simulated directory fsync ${code}`) as NodeJS.ErrnoException
+      error.code = code
+      throw error
+    }
+    return realSync.call(this)
+  })
+}
+
 function appendClosedTurn(session: Session): void {
   session.append('turn/start', { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } })
   session.append('user/message', {
@@ -112,6 +129,19 @@ describe('SessionPersistenceJsonl: format helpers', () => {
   it('encodeSegment rejects an empty id', () => {
     expect(() => encodeSegment('')).toThrow(/empty/)
   })
+
+  it('resolves a relative custom root before locating a session', async () => {
+    const absoluteRoot = await freshRoot()
+    const ctx = new Context()
+    await ctx.plugin(SessionStore)
+    const fiber = await ctx.plugin(SessionPersistenceJsonl, { root: relative(process.cwd(), absoluteRoot) })
+    const m = meta('relative-location', '/work')
+    expect(ctx.sessionPersistence.locate(m)).toEqual({
+      kind: 'jsonl',
+      path: logPath(resolve(absoluteRoot), '/work', m.id),
+    })
+    await fiber.dispose()
+  })
 })
 
 describe('SessionPersistenceJsonl: durability and crash semantics', () => {
@@ -126,8 +156,13 @@ describe('SessionPersistenceJsonl: durability and crash semantics', () => {
 
   it('lazy materialization: create() writes no file until the first append', async () => {
     const m = meta('lazy', '/work')
+    const location = ctx.sessionPersistence.locate(m)
+    expect(location).toEqual({ kind: 'jsonl', path: logPath(root, '/work', m.id) })
+    expect(isAbsolute(location!.path)).toBe(true)
+
     await ctx.sessionPersistence.create(m)
-    // nothing on disk yet
+    // locate() is a pure target-path calculation: neither it nor create()
+    // materializes a file before the first append.
     const dir = sessionDir(root, '/work')
     await expect(stat(logPath(root, '/work', m.id))).rejects.toThrow()
     expect((await ctx.sessionPersistence.list()).map(h => h.id)).not.toContain(m.id)
@@ -139,6 +174,26 @@ describe('SessionPersistenceJsonl: durability and crash semantics', () => {
     void dir
   })
 
+  it('keeps the same location on resume and gives a fork its own location', async () => {
+    const parent = meta('location-parent', '/work')
+    const parentLocation = ctx.sessionPersistence.locate(parent)
+    await ctx.sessionPersistence.create(parent)
+    await ctx.sessionPersistence.append(parent.id, oneTurnLog())
+
+    const loaded = await ctx.sessionPersistence.load(parent.id)
+    expect(ctx.sessionPersistence.locate(loaded.meta)).toEqual(parentLocation)
+
+    const child = {
+      ...loaded.meta,
+      id: SessionId('location-child'),
+      parentSession: parent.id,
+      seedLength: loaded.events.length,
+    }
+    const childLocation = ctx.sessionPersistence.locate(child)
+    expect(childLocation?.path).not.toBe(parentLocation?.path)
+    expect(childLocation).toEqual({ kind: 'jsonl', path: logPath(root, '/work', child.id) })
+  })
+
   it('round-trip is byte-identical (incl. assistant/chunk verbatim)', async () => {
     const m = meta('chunks')
     const log: SessionEvent[] = [
@@ -146,7 +201,7 @@ describe('SessionPersistenceJsonl: durability and crash semantics', () => {
       { type: 'step/start', seq: 1, time: 2, data: { turn: 1, step: 1 } },
       { type: 'assistant/chunk', seq: 2, time: 3, data: { turn: 1, step: 1, chunk: { type: 'text-delta', index: 0, text: 'he' } } },
       { type: 'assistant/chunk', seq: 3, time: 4, data: { turn: 1, step: 1, chunk: { type: 'text-delta', index: 0, text: 'llo' } } },
-      { type: 'assistant/message', seq: 4, time: 5, data: { turn: 1, step: 1, content: [{ type: 'text', text: 'hello' }] }, surfaceOp: 'append', sourceEventSeqs: [2, 3] },
+      { type: 'assistant/message', seq: 4, time: 5, data: { turn: 1, step: 1, content: [{ type: 'text', text: 'hello' }], provenance: { provider: 'mock', model: 'mock' } }, surfaceOp: 'append', sourceEventSeqs: [2, 3] },
       { type: 'step/end', seq: 5, time: 6, data: { turn: 1, step: 1 } },
       { type: 'turn/end', seq: 6, time: 7, data: { turn: 1, reason: { kind: 'completed' } } },
     ]
@@ -156,6 +211,40 @@ describe('SessionPersistenceJsonl: durability and crash semantics', () => {
     expect(loaded.events).toEqual(log) // chunks preserved, contiguous seqs
   })
 
+  it('rejects a stored v0 log containing a legacy request/header-delta event', async () => {
+    const m = meta('legacy-header-delta', '/legacy')
+    const path = logPath(root, m.cwd, m.id)
+    await mkdir(sessionDir(root, m.cwd), { recursive: true })
+    await writeFile(path, [
+      JSON.stringify(toHeaderLine(m)),
+      JSON.stringify({ type: 'turn/start', seq: 0, time: 1, data: { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } } }),
+      JSON.stringify({ type: 'request/header-delta', seq: 1, time: 2, data: { config: { model: 'legacy' } } }),
+      JSON.stringify({ type: 'turn/end', seq: 2, time: 3, data: { turn: 1, reason: { kind: 'completed' } } }),
+      '',
+    ].join('\n'))
+
+    await expect(ctx.sessionPersistence.load(m.id)).rejects.toThrow(/unsupported legacy request\/header-delta event at seq 1/)
+  })
+
+  it('rejects a stored v0 full header carrying the legacy fallback reason', async () => {
+    const m = meta('legacy-header-fallback', '/legacy')
+    const path = logPath(root, m.cwd, m.id)
+    await mkdir(sessionDir(root, m.cwd), { recursive: true })
+    await writeFile(path, [
+      JSON.stringify(toHeaderLine(m)),
+      JSON.stringify({
+        type: 'request/header',
+        seq: 0,
+        time: 1,
+        data: { header: { config: { model: 'legacy' } }, reason: 'fallback' },
+      }),
+      '',
+    ].join('\n'))
+
+    await expect(ctx.sessionPersistence.load(m.id))
+      .rejects.toThrow(/unsupported legacy request\/header reason "fallback" at seq 0/)
+  })
+
   it('persists a forked child seed through the existing session write path', async () => {
     const source = ctx.sessions.create(SessionId('persist-parent'), { meta: { cwd: '/workspace' } })
     appendClosedTurn(source)
@@ -264,6 +353,28 @@ describe('SessionPersistenceJsonl: durability and crash semantics', () => {
     expect(loaded.events.map(e => e.seq)).toEqual([0, 1, 2, 3, 4, 5, 6, 7])
   })
 
+  it('keeps file fsync mandatory while tolerating unsupported Windows directory fsync', async () => {
+    await rejectDirectorySync('EPERM')
+    const backend = ctx.sessionPersistence as SessionPersistenceJsonl
+    backend.internals.platform = 'win32'
+    const m = meta('windows-directory-sync')
+    await ctx.sessionPersistence.create(m)
+    await expect(ctx.sessionPersistence.append(m.id, oneTurnLog())).resolves.toBeUndefined()
+    expect((await ctx.sessionPersistence.load(m.id)).events).toEqual(oneTurnLog())
+  })
+
+  it.each([
+    ['linux', 'EPERM'],
+    ['win32', 'EIO'],
+  ] as const)('surfaces directory fsync errors on %s with %s', async (platform, code) => {
+    await rejectDirectorySync(code)
+    const backend = ctx.sessionPersistence as SessionPersistenceJsonl
+    backend.internals.platform = platform
+    const m = meta(`directory-sync-${platform}-${code}`)
+    await ctx.sessionPersistence.create(m)
+    await expect(ctx.sessionPersistence.append(m.id, oneTurnLog())).rejects.toMatchObject({ code })
+  })
+
   it('load returns a meta copy: mutating it does not corrupt backend pathing', async () => {
     const m = meta('meta-copy', '/proj')
     await ctx.sessionPersistence.create(m)
@@ -436,7 +547,7 @@ describe('SessionPersistenceJsonl: packed chunk rows (packChunks: true)', () =>
       { type: 'turn/start', seq: 0, time: 1, data: { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } } },
       { type: 'step/start', seq: 1, time: 2, data: { turn: 1, step: 1 } },
       ...deltas,
-      { type: 'assistant/message', seq: 7, time: 8, data: { turn: 1, step: 1, content: [{ type: 'text', text: 't0t1t2t3t4' }] }, surfaceOp: 'append', sourceEventSeqs: [2, 3, 4, 5, 6] },
+      { type: 'assistant/message', seq: 7, time: 8, data: { turn: 1, step: 1, content: [{ type: 'text', text: 't0t1t2t3t4' }], provenance: { provider: 'mock', model: 'mock' } }, surfaceOp: 'append', sourceEventSeqs: [2, 3, 4, 5, 6] },
       { type: 'step/end', seq: 8, time: 9, data: { turn: 1, step: 1 } },
       { type: 'turn/end', seq: 9, time: 10, data: { turn: 1, reason: { kind: 'completed' } } },
     ]

packages/session-persistence/session-persistence-sqlite/README.md

@@ -1,20 +1,24 @@
 # @deepseek-ai/dsh-session-persistence-sqlite
 
-A SQLite durable session-persistence backend — a second `SessionPersistence` implementation ([session persistence](../../../docs/rfc/implemented/architecture/2026-06-14-session-persistence.md)), built to validate that the abstract seam and the shared `runPersistenceContract` suite are genuinely backend-agnostic. It satisfies the SAME contract as `dsh-session-persistence-jsonl` (append-only, contiguous-seq, lazy materialization, interrupted-turn close on load), expressed over `node:sqlite` rows instead of file bytes.
+A SQLite durable session-persistence backend — a second `SessionPersistence` implementation ([session persistence](../../../.agents/notes/implemented/architecture/2026-06-14-session-persistence.md)), built to validate that the abstract seam and the shared `runPersistenceContract` suite are genuinely backend-agnostic. It satisfies the SAME contract as `dsh-session-persistence-jsonl` (append-only, contiguous-seq, lazy materialization, interrupted-turn close on load), expressed over `node:sqlite` rows instead of file bytes.
+
+`locate(meta)` returns `undefined`: all sessions share one database, so there is no honest independent per-session transcript path.
 
 > **TODO:** this backend talks to `node:sqlite` directly. If a cordis database service (`cordis/db` / a `@cordisjs` SQL driver plugin) is adopted, route through that instead of holding a raw `DatabaseSync` here — the contract surface (`SessionPersistence`) would not change, only the storage driver.
 
 ## Storage model
 
-Each `SessionEvent` maps 1:1 onto a row in an `events` table `(session_id, seq, type, time, data, source_event_seqs, surface_op)` — `data` is the event payload as JSON text, so the row shape is the event verbatim (including `assistant/chunk`, keeping `seq` contiguous). The two `TEXT` columns `source_event_seqs` and `surface_op` are nullable; they store the event's optional surface-metadata fields (see [session surface](../../../docs/rfc/implemented/architecture/2026-06-18-session-surface.md)). Out-of-log metadata (`SessionHeader`) lives in a `sessions` row. A `sessions` row is written only by the first `append` — its existence is the lazy-materialization signal (`list` reports exactly the sessions that have a row), so no separate column is needed.
+Each `SessionEvent` maps 1:1 onto a row in an `events` table `(session_id, seq, type, time, data, source_event_seqs, surface_op)` — `data` is the event payload as JSON text, so the row shape is the event verbatim (including `assistant/chunk`, keeping `seq` contiguous). The two `TEXT` columns `source_event_seqs` and `surface_op` are nullable; they store the event's optional surface-metadata fields (see [session surface](../../../.agents/notes/implemented/architecture/2026-06-18-session-surface.md)). Out-of-log metadata (`SessionHeader`) lives in a `sessions` row. A `sessions` row is written only by the first `append` — its existence is the lazy-materialization signal (`list` reports exactly the sessions that have a row), so no separate column is needed.
 
 The repository's Node range supports unflagged `node:sqlite`. The database enables foreign keys and uses the configured journal mode (`wal` by default; use a rollback mode where WAL shared-memory files are unsuitable). `PRAGMA user_version` stores the table-layout version; databases with any other version are rejected because this unreleased format has no migrations.
 
+On filesystems with POSIX modes, the backend requests mode `0700` for missing directories and exclusively creates a missing database with mode `0600` before SQLite opens it; the process umask may further restrict both. New WAL, shared-memory, and persistent rollback-journal sidecars receive the database's resulting owner-only mode. Existing directories, database files, and sidecars keep their modes; filesystem setup errors other than an existing database fail initialization. These defaults prevent incidental exposure through a permissive process umask, but do not protect database confidentiality or integrity when another principal can replace the database entry in its parent directory.
+
 ## Contract semantics over rows
 
 - **Append = a transaction.** `append` runs `BEGIN`/`COMMIT` around the batch: it materializes the `sessions` row (if still lazy) and INSERTs every event, asserting the contiguous-seq contract first (the first event's `seq` must equal the stored next-seq). A mid-batch failure (a UNIQUE violation on a duplicated seq) rolls back entirely, so the stored log and the in-memory cursor stay consistent. (`load()` already balanced the stored log, so `append` never has to repair a crash tail.)
 - **Lazy materialization.** `create()` records intent in memory only — no row is written until the first `append`. A created-but-never-appended session has no `sessions` row, so it is absent from `list()` (which reports exactly the sessions that have a row).
-- **Interrupted-turn close on load.** `load()` implements the shared [crash-recovery contract](../../../docs/rfc/implemented/architecture/2026-06-14-session-persistence.md): preserve the valid interrupted turn, append its synthetic closing events in one transaction, and remove only a torn tail row. Committed parse errors or sequence gaps make the session unloadable. Because recovery mutates stored rows, the next append starts from a balanced log and accurate cursor.
+- **Interrupted-turn close on load.** `load()` implements the shared [crash-recovery contract](../../../.agents/notes/implemented/architecture/2026-06-14-session-persistence.md): preserve the valid interrupted turn, append its synthetic closing events in one transaction, and remove only a torn tail row. Committed parse errors or sequence gaps make the session unloadable. Because recovery mutates stored rows, the next append starts from a balanced log and accurate cursor.
 
 ## Configuration (schemastery)
 
@@ -33,9 +37,17 @@ Like the JSONL backend, the plugin also installs the `session/event` → buffer
 
 ### Resumed conversation history
 
-**What the model sees**: SQLite storage contributes no live prompt or schema. Loading restores the same surface history as JSONL and preserves prior headers for reconstruction; the new loop composes its current envelope. Each unanswered call in interrupted rows is balanced with the exact error text `Tool call interrupted by a crash; no result was recorded.` Row metadata and raw chunks are not messages.
+#### What the model sees
 
-**Token effect**: Zero live-request tokens. Resume restores retained history and pays the current envelope, plus the quoted repair result for each interrupted call.
+SQLite storage contributes no live prompt or schema. Loading restores the same surface history as JSONL and preserves prior headers for reconstruction; the new loop composes its current envelope. Each unanswered call in interrupted rows is balanced with the exact error text `Tool call interrupted by a crash; no result was recorded.` Row metadata and raw chunks are not messages.
+
+#### Token effect
+
+Zero live-request tokens. Resume restores retained history and pays the current envelope, plus the quoted repair result for each interrupted call.
+
+#### KV Cache effect
+
+SQLite storage does not mutate live request prefixes. A resumed loop can reuse provider cache only when its reconstructed history, current envelope, and model route match; crash-repair results append.
 
 ## Known Limitations and Deferred Work
 

packages/session-persistence/session-persistence-sqlite/src/index.ts

@@ -1,18 +1,19 @@
 /**
  * SQLite durable session-persistence backend. It maps each session header and
  * event to rows, and delegates write-path orchestration to
- * {@link PersistenceCoordinator}.
+ * {@link PersistenceCoordinator}. It has no independent per-session artifact,
+ * so its locator returns `undefined`.
  * @module @deepseek-ai/dsh-session-persistence-sqlite
  */
 
 import { Context } from 'cordis'
 import z from 'schemastery'
 import { DatabaseSync } from 'node:sqlite'
-import { mkdir } from 'node:fs/promises'
+import { mkdir, open } from 'node:fs/promises'
 import { dirname, resolve } from 'node:path'
 import {
   SessionPersistence, PersistenceCoordinator,
-  type PersistenceBackend, type StoredPrefix,
+  type PersistenceBackend, type SessionLocation, type StoredPrefix,
 } from '@deepseek-ai/dsh-session-persistence'
 import type { SessionEvent, SurfaceEventType, SessionId, SessionHeader } from '@deepseek-ai/dsh-session'
 import {
@@ -34,12 +35,32 @@ function surfaceBindings(event: SessionEvent): [string | null, string | null] {
   ]
 }
 
+/**
+ * Exclusively create a missing database file with owner-only permissions.
+ * Existing files retain their modes, and errors other than `EEXIST` propagate.
+ * `DatabaseSync` reopens by path, so this does not protect confidentiality or
+ * integrity when another principal can replace the database entry in its parent
+ * directory.
+ */
+async function createDatabaseFile(path: string): Promise<void> {
+  try {
+    const handle = await open(path, 'wx', 0o600)
+    await handle.close()
+  } catch (error) {
+    if ((error as NodeJS.ErrnoException).code !== 'EEXIST') throw error
+  }
+}
+
 /** Plugin configuration. */
 export interface Config {
   /**
    * Filesystem path to the SQLite database file. The special value `:memory:`
-   * opens an in-process database (tests); a file path is created (with parent
-   * dirs) on construction.
+   * opens an in-process database (tests). On filesystems with POSIX modes,
+   * missing directories and databases are created owner-only; existing path
+   * modes are preserved. Filesystem setup errors other than an existing database
+   * fail initialization. The backend does not protect confidentiality or
+   * integrity when another principal can replace the database entry in its
+   * parent directory.
    */
   path: string
   /**
@@ -87,6 +108,7 @@ export class SessionPersistenceSqlite extends SessionPersistence implements Pers
     if (path !== ':memory:') {
       const abs = resolve(path)
       await mkdir(dirname(abs), { recursive: true, mode: 0o700 })
+      await createDatabaseFile(abs)
       this.db = openDatabase(abs, journalMode)
     } else {
       this.db = openDatabase(path, journalMode)
@@ -95,6 +117,11 @@ export class SessionPersistenceSqlite extends SessionPersistence implements Pers
 
   // --- SessionPersistence service surface (delegated to the coordinator) ---
 
+  /** SQLite has one database, not an independent local artifact per session. */
+  locate(_meta: SessionHeader): SessionLocation | undefined {
+    return undefined
+  }
+
   create(meta: SessionHeader): Promise<void> {
     return this.coordinator.create(meta)
   }

packages/session-persistence/session-persistence-sqlite/tests/sqlite.spec.ts

@@ -1,9 +1,9 @@
 import { afterEach, describe, expect, it } from 'vitest'
 import { Context } from 'cordis'
 import { existsSync } from 'node:fs'
-import { mkdtemp, rm } from 'node:fs/promises'
+import { chmod, mkdtemp, rm, stat, writeFile } from 'node:fs/promises'
 import { tmpdir } from 'node:os'
-import { join } from 'node:path'
+import { dirname, join } from 'node:path'
 import SessionStore, { SessionId } from '@deepseek-ai/dsh-session'
 import type { Session, SessionEvent, SurfaceEvent, SurfaceEventType } from '@deepseek-ai/dsh-session'
 import SessionPersistenceSqlite, { SCHEMA_VERSION } from '@deepseek-ai/dsh-session-persistence-sqlite'
@@ -153,6 +153,48 @@ describe('scanRows', () => {
 })
 
 describe('SessionPersistenceSqlite: durability and crash semantics', () => {
+  it('rejects a stored v0 log containing a legacy request/header-delta event', async () => {
+    const path = await freshDbPath()
+    const m = meta('legacy-header-delta', '/legacy')
+    const db = openDatabase(path, 'wal')
+    db.prepare('INSERT INTO sessions (id, version, created_at, cwd, parent_session, seed_length) VALUES (?, ?, ?, ?, NULL, NULL)')
+      .run(m.id, m.version, m.createdAt, m.cwd ?? null)
+    const insert = db.prepare('INSERT INTO events (session_id, seq, type, time, data) VALUES (?, ?, ?, ?, ?)')
+    insert.run(m.id, 0, 'turn/start', 1, JSON.stringify({ turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } }))
+    insert.run(m.id, 1, 'request/header-delta', 2, JSON.stringify({ config: { model: 'legacy' } }))
+    insert.run(m.id, 2, 'turn/end', 3, JSON.stringify({ turn: 1, reason: { kind: 'completed' } }))
+    db.close()
+
+    const mounted = await backend(path)
+    await expect(mounted.ctx.sessionPersistence.load(m.id)).rejects.toThrow(/unsupported legacy request\/header-delta event at seq 1/)
+    await mounted.dispose()
+  })
+
+  it('rejects a stored v0 full header carrying the legacy fallback reason', async () => {
+    const path = await freshDbPath()
+    const m = meta('legacy-header-fallback', '/legacy')
+    const db = openDatabase(path, 'wal')
+    db.prepare('INSERT INTO sessions (id, version, created_at, cwd, parent_session, seed_length) VALUES (?, ?, ?, ?, NULL, NULL)')
+      .run(m.id, m.version, m.createdAt, m.cwd ?? null)
+    db.prepare('INSERT INTO events (session_id, seq, type, time, data) VALUES (?, ?, ?, ?, ?)')
+      .run(m.id, 0, 'request/header', 1, JSON.stringify({
+        header: { config: { model: 'legacy' } },
+        reason: 'fallback',
+      }))
+    db.close()
+
+    const mounted = await backend(path)
+    await expect(mounted.ctx.sessionPersistence.load(m.id))
+      .rejects.toThrow(/unsupported legacy request\/header reason "fallback" at seq 0/)
+    await mounted.dispose()
+  })
+
+  it('has no independent per-session log location', async () => {
+    const { ctx, dispose } = await backend()
+    expect(ctx.sessionPersistence.locate(meta('sqlite-location'))).toBeUndefined()
+    await dispose()
+  })
+
   it('an interrupted turn (rows after the last turn/end) is PRESERVED and closed during load', async () => {
     const path = await freshDbPath()
     const m = meta('crash')
@@ -348,6 +390,61 @@ describe('SessionPersistenceSqlite: durability and crash semantics', () => {
 })
 
 describe('SessionPersistenceSqlite: edge cases', () => {
+  it('creates a new database and WAL sidecars with owner-only modes without changing its parent mode', async () => {
+    if (process.platform === 'win32') return
+    const path = await freshDbPath()
+    const dir = dirname(path)
+    await chmod(dir, 0o755)
+
+    const b = await backend(path)
+    await b.ctx.sessionPersistence.list()
+
+    expect((await stat(dir)).mode & 0o777).toBe(0o755)
+    expect((await stat(path)).mode & 0o777).toBe(0o600)
+    expect((await stat(`${path}-wal`)).mode & 0o777).toBe(0o600)
+    expect((await stat(`${path}-shm`)).mode & 0o777).toBe(0o600)
+    await b.dispose()
+  })
+
+  it('creates a persistent rollback journal with owner-only mode', async () => {
+    if (process.platform === 'win32') return
+    const path = await freshDbPath()
+    const ctx = new Context()
+    await ctx.plugin(SessionStore)
+    const fiber = await ctx.plugin(SessionPersistenceSqlite, { path, journalMode: 'persist' })
+    const m = meta('persist-permissions')
+
+    await ctx.sessionPersistence.create(m)
+    await ctx.sessionPersistence.append(m.id, oneTurnLog())
+
+    expect((await stat(path)).mode & 0o777).toBe(0o600)
+    expect((await stat(`${path}-journal`)).mode & 0o777).toBe(0o600)
+    await fiber.dispose()
+  })
+
+  it('preserves the mode of an existing database file', async () => {
+    if (process.platform === 'win32') return
+    const path = await freshDbPath()
+    await writeFile(path, '', { mode: 0o644 })
+    await chmod(path, 0o644)
+
+    const ctx = new Context()
+    await ctx.plugin(SessionStore)
+    const fiber = await ctx.plugin(SessionPersistenceSqlite, { path, journalMode: 'delete' })
+    await ctx.sessionPersistence.list()
+
+    expect((await stat(path)).mode & 0o777).toBe(0o644)
+    await fiber.dispose()
+  })
+
+  it('surfaces an invalid database path during pre-creation', async () => {
+    const path = await freshDbPath()
+    const b = await backend(`${path}\0`)
+
+    await expect(b.ctx.sessionPersistence.list()).rejects.toMatchObject({ code: 'ERR_INVALID_ARG_VALUE' })
+    await b.dispose()
+  })
+
   it('append rolls back and rethrows when an event INSERT fails inside the transaction', async () => {
     const path = await freshDbPath()
     const m = meta('rollback-insert')
@@ -471,7 +568,7 @@ describe('surface field round-trip', () => {
     const session = ctx.sessions.create(SessionId('roundtrip-surface'))
     session.append('turn/start', { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } })
     session.append('user/message', { content: [{ type: 'text', text: 'hi' }], source: { kind: 'user' } }, { surfaceOp: 'append' })
-    session.append('assistant/message', { turn: 1, step: 1, content: [] }, { surfaceOp: 'append', sourceEventSeqs: [0] })
+    session.append('assistant/message', { provenance: { provider: 'mock', model: 'mock' }, turn: 1, step: 1, content: [] }, { surfaceOp: 'append', sourceEventSeqs: [0] })
     session.append('turn/end', { turn: 1, reason: { kind: 'completed' } })
     await ctx.parallel('session/flush', session)
     const loaded = await ctx.sessionPersistence.load(SessionId('roundtrip-surface'))

packages/session-persistence/session-persistence/README.md

@@ -1,6 +1,6 @@
 # @deepseek-ai/dsh-session-persistence
 
-The abstract durable session-persistence seam (`ctx.sessionPersistence`). Defines WHAT a persistence backend does — durably store, reload, and list sessions — without saying HOW. Mirrors the `dsh-bash` capability-seam template ([capability seams](../../../docs/rfc/implemented/architecture/2026-06-13-capability-seams.md)): an abstract service here, a concrete implementation in a sibling package, consumers that inject the interface.
+The abstract durable session-persistence seam (`ctx.sessionPersistence`). Defines WHAT a persistence backend does — durably store, reload, and list sessions — without saying HOW. Mirrors the `dsh-bash` capability-seam template ([capability seams](../../../.agents/notes/implemented/architecture/2026-06-13-capability-seams.md)): an abstract service here, a concrete implementation in a sibling package, consumers that inject the interface.
 
 The persisted unit IS the existing `SessionEvent` (event-sourced model — the log is the single source of truth), so there is no parallel "persisted message" type. Metadata that is NOT replayable conversation state (format version, cwd, lineage, seed boundary) travels separately as `SessionHeader`, owned by `dsh-session` and re-exported here.
 
@@ -8,6 +8,7 @@ The persisted unit IS the existing `SessionEvent` (event-sourced model — the l
 
 | Method | Contract |
 |---|---|
+| `locate(meta): SessionLocation \| undefined` | Resolve an absolute per-session artifact target without I/O or materialization. Backends without an independent local artifact return `undefined`. |
 | `create(meta): Promise<void>` | Register a new session's metadata. MAY defer the physical write until the first `append` (lazy materialization). |
 | `append(id, events): Promise<void>` | Durably persist a batch (from the `session/flush` drain). Append-only; first event `seq` == stored next-seq after any repair; rejects non-JSON-serializable data naming the offending type. |
 | `load(id): Promise<{ meta; events }>` | Reload meta + log. Preserves an interrupted (unclosed) final turn and closes it with synthetic closers — an error `tool/result` per unanswered `tool-call`, then `step/end?`+`turn/end {interrupted}` (a turn can be huge — never truncated); only a torn tail fragment is dropped. Events contiguous (`events[i].seq === i`); rejects a committed-region gap/parse error or unknown `version`. |
@@ -22,7 +23,11 @@ The persisted unit IS the existing `SessionEvent` (event-sourced model — the l
 
 ## The write coordinator
 
-`PersistenceCoordinator` owns per-id state, write-behind buffers and serialization, the `session/event` → `session/flush` drain, lazy materialization, crash-tail repair, session adoption, and quiescent disposal. A first-party backend composes one, implements the small `PersistenceBackend` storage hook interface, and delegates its four public service methods. JSONL and SQLite therefore share lifecycle correctness while retaining different storage primitives; see the [coordinator RFC](../../../docs/rfc/implemented/architecture/2026-06-18-shared-persistence-write-coordinator.md).
+`PersistenceCoordinator` owns per-id state, write-behind buffers and serialization, the `session/event` → `session/flush` drain, lazy materialization, crash-tail repair, session adoption, and quiescent disposal. A first-party backend composes one, implements the small `PersistenceBackend` storage hook interface, and delegates its four public service methods. JSONL and SQLite therefore share lifecycle correctness while retaining different storage primitives; see the [coordinator Agent Note](../../../.agents/notes/implemented/architecture/2026-06-18-shared-persistence-write-coordinator.md).
+
+When a live session emits `session/disposed`, the coordinator waits for its initialization, serializes a final buffer drain, then releases every map entry owned by that exact `Session` object. A failed final drain keeps the pending buffer for backend teardown to retry. Backend teardown stops event admission first, awaits all in-flight session retirements and remaining per-id operations, drains any retained buffers, and only then closes the storage handle.
+
+The side-effect-free `locate` query remains backend-owned because it describes storage topology rather than write orchestration.
 
 The `PersistenceBackend<TornMarker>` hooks (the only seam between the coordinator and storage):
 
@@ -36,7 +41,7 @@ The `PersistenceBackend<TornMarker>` hooks (the only seam between the coordinato
 | `list()` | List all stored metadata. |
 | `close?()` | Optional lifecycle teardown (e.g. close a db handle), awaited after the dispose drain. |
 
-The `tornMarker` is fully OPAQUE: the coordinator only tests `!== undefined` and round-trips it to `commitRepair`, never inspecting its value (the JSONL backend uses the byte offset to truncate to, the SQLite backend the seq to delete from). The public `SessionPersistence` service shape is unchanged, so a third-party backend MAY still implement the abstract service directly without the coordinator. See [the write-coordinator RFC](../../../docs/rfc/implemented/architecture/2026-06-18-shared-persistence-write-coordinator.md).
+The `tornMarker` is fully OPAQUE: the coordinator only tests `!== undefined` and round-trips it to `commitRepair`, never inspecting its value (the JSONL backend uses the byte offset to truncate to, the SQLite backend the seq to delete from). The public `SessionPersistence` service shape is unchanged, so a third-party backend MAY still implement the abstract service directly without the coordinator. See [the write-coordinator Agent Note](../../../.agents/notes/implemented/architecture/2026-06-18-shared-persistence-write-coordinator.md).
 
 ## Testing backends
 
@@ -44,17 +49,25 @@ Import `runPersistenceContract` from `tests/contract.ts` (the public-API contrac
 
 Three backends run these suites: an in-memory reference (in `tests/`), `dsh-session-persistence-jsonl` (append-only file log) and `dsh-session-persistence-sqlite` (`node:sqlite`, each `SessionEvent` one row `(session_id, seq, type, time, data, source_event_seqs, surface_op)`). All passing the same contract + coordinator suite is the proof that the seam is genuinely backend-agnostic — lazy materialization, crash-tail-on-load, and contiguous-seq hold identically over file bytes and over a transactional store.
 
-## Metadata types
+## Metadata and location types
 
-Re-exported from `dsh-session`: `SessionHeader` (immutable session metadata: `version`, `id`, `createdAt`, `cwd?`, `parentSession?`, `seedLength?`).
+Re-exported from `dsh-session`: `SessionHeader` (immutable session metadata: `version`, `id`, `createdAt`, `cwd?`, `parentSession?`, `seedLength?`). `SessionLocation` is `{ readonly kind: string; readonly path: string }`; its path is an absolute backend target, not proof that the artifact exists or contains an unflushed turn.
 
 ## Model Experience
 
 ### Resumed conversation history
 
-**What the model sees**: This seam adds no prompt or schema. Resume restores stored surface events as message history; stored request headers reconstruct earlier calls, while the new loop composes the current system prompt, tools, and session prefix for its next request. Crash repair inserts exactly `Tool call interrupted by a crash; no result was recorded.` as the error result for each unanswered tool call.
+#### What the model sees
 
-**Token effect**: Zero tokens during ordinary persistence. Resume restores retained history cost and pays the current request envelope normally; each repaired call adds the quoted retained error text.
+This seam adds no prompt or schema. Resume restores stored surface events as message history; stored request headers reconstruct earlier calls, while the new loop composes the current system prompt, tools, and session prefix for its next request. Crash repair inserts exactly `Tool call interrupted by a crash; no result was recorded.` as the error result for each unanswered tool call.
+
+#### Token effect
+
+Zero tokens during ordinary persistence. Resume restores retained history cost and pays the current request envelope normally; each repaired call adds the quoted retained error text.
+
+#### KV Cache effect
+
+Persistence does not mutate live request prefixes. A resumed loop can reuse provider cache only when its reconstructed history, current envelope, and model route match; crash-repair results append without rewriting earlier history.
 
 ## Known Limitations and Deferred Work
 

packages/session-persistence/session-persistence/src/coordinator.ts

@@ -118,6 +118,20 @@ function seedCoversPrefix(seed: readonly SessionEvent[], prefix: readonly Sessio
     })
 }
 
+/** Reject events from an obsolete v0 vocabulary that this build cannot replay. */
+function assertSupportedEvents(events: readonly SessionEvent[], id: SessionId): void {
+  const legacyType: string = 'request/header-delta'
+  const legacy = events.find(event => event.type === legacyType)
+  if (legacy !== undefined) {
+    throw new Error(`session "${id}" contains unsupported legacy request/header-delta event at seq ${legacy.seq}`)
+  }
+  const fallback = events.find(event => event.type === 'request/header'
+    && (event.data as { reason?: string }).reason === 'fallback')
+  if (fallback !== undefined) {
+    throw new Error(`session "${id}" contains unsupported legacy request/header reason "fallback" at seq ${fallback.seq}`)
+  }
+}
+
 /**
  * Owns the backend-agnostic session write-path orchestration. A backend
  * constructs one (`new PersistenceCoordinator(ctx, this)`), implements
@@ -126,7 +140,8 @@ function seedCoversPrefix(seed: readonly SessionEvent[], prefix: readonly Sessio
  *
  * All per-id operations are serialized (a per-id promise chain) so concurrent
  * flushes / a flush racing a load never interleave storage writes. The
- * constructor installs the write-path listeners and the dispose effect.
+ * constructor installs the write-path listeners, per-session retirement, and
+ * the backend dispose effect.
  *
  * @typeParam TornMarker - the backend's opaque torn-tail repair token.
  */
@@ -146,6 +161,8 @@ export class PersistenceCoordinator<TornMarker = unknown> {
    * observation boundary; callers do not inspect this bookkeeping directly.
    */
   private inits = new Map<Session, Promise<void>>()
+  /** Final drains started by fire-and-forget session disposal notifications. */
+  private retirements = new Set<Promise<void>>()
 
   constructor(private ctx: Context, private backend: PersistenceBackend<TornMarker>) {
     this.installWritePath()
@@ -204,6 +221,11 @@ export class PersistenceCoordinator<TornMarker = unknown> {
   }
 
   private async appendCore(id: SessionId, events: readonly SessionEvent[]): Promise<void> {
+    // Every append route converges here: the public service, live write-behind
+    // drains, and HMR seed/suffix adoption. Keep vocabulary rejection at that
+    // shared boundary so a stale JavaScript plugin cannot persist an event that
+    // this same backend will refuse to load.
+    assertSupportedEvents(events, id)
     if (events.length === 0) return
     let state = this.states.get(id)
     if (state === undefined) state = await this.adopt(id) // calls loadCore, not load
@@ -238,6 +260,7 @@ export class PersistenceCoordinator<TornMarker = unknown> {
     if (stored === undefined) throw new Error(`session "${id}" not found`)
     const { meta, events, tornMarker } = stored
     this.assertVersion(meta)
+    assertSupportedEvents(events, id)
 
     // Preserve complete interrupted events and synthesize only missing closers.
     const closers = interruptedTurnClosers(events)
@@ -267,7 +290,13 @@ export class PersistenceCoordinator<TornMarker = unknown> {
     const next = prior.then(op, op)
     // Keep the chain alive but swallow this op's rejection for the NEXT waiter
     // (the caller still sees the real rejection via `next`).
-    this.chains.set(id, next.then(() => undefined, () => undefined))
+    const tail = next.then(() => undefined, () => undefined)
+    this.chains.set(id, tail)
+    // Settled tails carry no serialization value. Delete only the exact tail
+    // installed above: a later operation may already have replaced it.
+    void tail.then(() => {
+      if (this.chains.get(id) === tail) this.chains.delete(id)
+    })
     return next
   }
 
@@ -293,27 +322,12 @@ export class PersistenceCoordinator<TornMarker = unknown> {
   private installWritePath(): void {
     const ctx = this.ctx
 
-    // Capture the header on creation; persist a fork's seed once. Record the init
-    // promise so flush/dispose can await it (onCreated is async).
-    ctx.on('session/created', (session) => { void this.initFor(session) })
-
-    // Session emits an owned frozen event. Keep a persistence-owned copy anyway
-    // so the write-behind queue owns exactly the record it will flush rather than
-    // retaining a product-layer record by identity. Serializability is guaranteed
-    // at the source, so structuredClone is safe.
-    ctx.on('session/event', (session, event) => {
-      let buffer = this.buffers.get(session)
-      if (!buffer) this.buffers.set(session, buffer = [])
-      buffer.push(structuredClone(event))
-    })
-
-    // Drain to the backend at the durability checkpoint.
-    ctx.on('session/flush', session => this.flush(session))
-
-    // Dispose must reach quiescence: await every init + final drain BEFORE
-    // returning, then close the backend's own resources (AFTER the drain), so no
-    // write lands after teardown and a close failure never MASKS a drain error.
+    // Register the disposer BEFORE the listeners. Cordis tears effects down in
+    // reverse registration order, so event admission closes before this final
+    // drain reaches quiescence and closes the backend.
     ctx.effect(() => async () => {
+      await this.awaitRetirements()
+
       let disposeError: unknown
       try {
         const errors = [
@@ -341,11 +355,63 @@ export class PersistenceCoordinator<TornMarker = unknown> {
       }
     }, `${this.backend.name} write path`)
 
+    // Capture the header on creation; persist a fork's seed once. Record the init
+    // promise so flush/dispose can await it (onCreated is async).
+    ctx.on('session/created', (session) => { void this.initFor(session) })
+
+    // Session emits an owned frozen event. Keep a persistence-owned copy anyway
+    // so the write-behind queue owns exactly the record it will flush rather than
+    // retaining a product-layer record by identity. Serializability is guaranteed
+    // at the source, so structuredClone is safe.
+    ctx.on('session/event', (session, event) => {
+      let buffer = this.buffers.get(session)
+      if (!buffer) this.buffers.set(session, buffer = [])
+      buffer.push(structuredClone(event))
+    })
+
+    // Drain to the backend at the durability checkpoint.
+    ctx.on('session/flush', session => this.flush(session))
+
+    // Session disposal is observe-only, so the coordinator observes the
+    // detached task itself and backend teardown awaits quiescence.
+    ctx.on('session/disposed', (session) => { this.retire(session) })
+
     // HMR: a hot reload does not replay session/created, so seed existing live
     // sessions (mirrors dsh-invariants).
     for (const session of ctx.sessions.list()) void this.initFor(session)
   }
 
+  /** Start, observe, and track one disposed session's final drain. */
+  private retire(session: Session): void {
+    const task = this.retireCore(session)
+    this.retirements.add(task)
+    const settled = (): void => { this.retirements.delete(task) }
+    void task.then(settled, (error: unknown) => {
+      settled()
+      this.ctx.logger.warn(`${this.backend.name}: session "${session.id}" retirement failed: ${String(error)}`)
+    })
+  }
+
+  /** Drain and release state owned by one exact disposed Session lifecycle. */
+  private async retireCore(session: Session): Promise<void> {
+    await this.inits.get(session)
+
+    const id = session.header.id
+    await this.serialize(id, async () => {
+      await this.drain(session)
+      this.buffers.delete(session)
+      this.inits.delete(session)
+      if (this.states.get(id)?.owner === session) this.states.delete(id)
+    })
+  }
+
+  /** Await every retirement admitted before listener teardown. */
+  private async awaitRetirements(): Promise<void> {
+    while (this.retirements.size > 0) {
+      await Promise.allSettled([...this.retirements])
+    }
+  }
+
   /** Start (once) the async init for a session and remember its promise. */
   private initFor(session: Session): Promise<void> {
     const existing = this.inits.get(session)
@@ -463,6 +529,7 @@ export class PersistenceCoordinator<TornMarker = unknown> {
   private async adoptLivePrefix(session: Session, seed: readonly SessionEvent[], stored: StoredPrefix<TornMarker>): Promise<void> {
     const { meta, events, tornMarker } = stored
     this.assertVersion(meta)
+    assertSupportedEvents(events, session.header.id)
     if (!seedCoversPrefix(seed, events)) {
       throw new Error(`session "${session.header.id}" already has a persisted log on disk that does not match this live session (id collision)`)
     }

packages/session-persistence/session-persistence/src/index.ts

@@ -21,6 +21,18 @@ declare module 'cordis' {
   }
 }
 
+/**
+ * A backend-resolved, per-session local artifact location. The path is an
+ * absolute target path and can name an artifact that has not materialized yet.
+ * Consumers must treat it as a location hint, never as an authorization token.
+ */
+export interface SessionLocation {
+  /** Backend-specific artifact kind, for example `jsonl`. */
+  readonly kind: string
+  /** Absolute path to this session's backend-owned artifact. */
+  readonly path: string
+}
+
 /**
  * Durable append-only session storage. Implementations preserve contiguous,
  * losslessly JSON-serializable events; {@link append} resolves only after
@@ -32,6 +44,15 @@ export abstract class SessionPersistence extends Service {
     super(ctx, 'sessionPersistence')
   }
 
+  /**
+   * Resolve this backend's independent local artifact for a session without
+   * reading, creating, flushing, or otherwise materializing it. Backends such
+   * as SQLite that do not own one artifact per session return `undefined`.
+   * @param meta - the immutable session header whose artifact is requested.
+   * @returns the backend-specific absolute location, when one exists.
+   */
+  abstract locate(meta: SessionHeader): SessionLocation | undefined
+
   /**
    * Register a new session's metadata. A backend MAY defer the physical write
    * until the first {@link append} (lazy materialization), in which case a

packages/session-persistence/session-persistence/tests/contract.ts

@@ -36,7 +36,7 @@ export function oneTurnLog(): SessionEvent[] {
     { type: 'turn/start', seq: 0, time: 1, data: { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } } },
     { type: 'user/message', seq: 1, time: 2, data: { content: [{ type: 'text', text: 'hi' }], source: { kind: 'user' } }, surfaceOp: 'append' },
     { type: 'step/start', seq: 2, time: 3, data: { turn: 1, step: 1 } },
-    { type: 'assistant/message', seq: 3, time: 4, data: { turn: 1, step: 1, content: [{ type: 'text', text: 'hello' }] }, surfaceOp: 'append' },
+    { type: 'assistant/message', seq: 3, time: 4, data: { turn: 1, step: 1, content: [{ type: 'text', text: 'hello' }], provenance: { provider: 'mock', model: 'mock' } }, surfaceOp: 'append' },
     { type: 'step/end', seq: 4, time: 5, data: { turn: 1, step: 1 } },
     { type: 'turn/end', seq: 5, time: 6, data: { turn: 1, reason: { kind: 'completed' } } },
   ]
@@ -136,7 +136,7 @@ export function runPersistenceContract(name: string, make: () => Promise<Contrac
           { type: 'step/start', seq: 7, time: 8, data: { turn: 2, step: 1 } },
           { type: 'assistant/message', seq: 8, time: 9, data: { turn: 2, step: 1, content: [
             { type: 'tool-call', id: CallId('call-x'), name: 'bash', arguments: '{}' },
-          ] } },
+          ], provenance: { provider: 'mock', model: 'mock' } } },
         ])
 
         const loaded = await persistence.load(m.id)

packages/session-persistence/session-persistence/tests/coordinator-contract.ts

@@ -9,7 +9,7 @@
  * @module @deepseek-ai/dsh-session-persistence/tests/coordinator-contract
  */
 
-import { describe, expect, it } from 'vitest'
+import { describe, expect, it, vi } from 'vitest'
 import { Context, type Fiber } from 'cordis'
 import SessionStore, { SESSION_FORMAT_VERSION, SessionId } from '@deepseek-ai/dsh-session'
 import type { Session, SessionEvent } from '@deepseek-ai/dsh-session'
@@ -401,7 +401,7 @@ export function runCoordinatorContract(name: string, makeFixture: () => Promise<
       }
     })
 
-    it('does NOT reclaim an id whose abandoned owner still has buffered (unflushed) events', async () => {
+    it('session disposal drains buffered events before retiring ownership', async () => {
       const fix = await makeFixture()
       const { ctx, fiber } = await freshCtx(fix)
       try {
@@ -413,13 +413,20 @@ export function runCoordinatorContract(name: string, makeFixture: () => Promise<
         // Append a turn but do NOT flush — events sit in the write-behind buffer.
         first.append('turn/start', { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } })
         first.append('turn/end', { turn: 1, reason: { kind: 'completed' } })
-        await firstFiber.dispose() // disposed before flush; not materialized, buffer pending
+        await firstFiber.dispose()
+
+        // Disposal is an observe-only notification. Poll storage rather than
+        // assuming the owning fiber awaits the coordinator's detached drain.
+        await vi.waitFor(async () => {
+          expect((await ctx.sessionPersistence.list()).map(meta => meta.id)).toContain(SessionId('buffered'))
+        })
+        expect((await ctx.sessionPersistence.load(SessionId('buffered'))).events.map(event => event.seq)).toEqual([0, 1])
 
         let reuse!: Session
         await ctx.plugin(Object.assign((inner: Context) => {
           reuse = inner.sessions.create(SessionId('buffered'), { meta: { cwd: WORK } })
         }, { inject: ['sessions'] }))
-        await expect(ctx.sessions.flush(reuse)).rejects.toThrow(/already bound to a different live session/)
+        await expect(ctx.sessions.flush(reuse)).rejects.toThrow(/persisted log|id collision/)
       } finally {
         await fiber.dispose()
         await fix.cleanup()

packages/session-persistence/session-persistence/tests/persistence.spec.ts

@@ -1,7 +1,7 @@
-import { describe, expect, it } from 'vitest'
+import { describe, expect, it, vi } from 'vitest'
 import { Context } from 'cordis'
 import SessionStore, { SessionId, isJsonValue } from '@deepseek-ai/dsh-session'
-import type { SessionEvent, SessionHeader } from '@deepseek-ai/dsh-session'
+import type { Session, SessionEvent, SessionHeader } from '@deepseek-ai/dsh-session'
 import {
   SessionPersistence, PersistenceCoordinator,
   type PersistenceBackend, type StoredPrefix,
@@ -12,9 +12,38 @@ import { runCoordinatorContract, type CoordinatorFixture } from './coordinator-c
 /** The durable store shape: materialized sessions only (no lazy entries). */
 type MemoryStore = Map<string, { meta: SessionHeader; events: SessionEvent[] }>
 
+/** An obsolete event fixture that emulates an untyped pre-change producer. */
+function legacyHeaderDelta(seq = 0): SessionEvent {
+  return {
+    type: 'request/header-delta',
+    seq,
+    time: 1,
+    data: { config: { model: 'legacy' } },
+  } as unknown as SessionEvent
+}
+
+/** An obsolete full-header reason fixture from the removed delta codec. */
+function legacyFallbackHeader(seq = 0): SessionEvent {
+  return {
+    type: 'request/header',
+    seq,
+    time: 1,
+    data: { header: { config: { model: 'legacy' } }, reason: 'fallback' },
+  } as unknown as SessionEvent
+}
+
 /** Optional plugin config: an EXTERNAL store shared across backend instances. */
 interface MemoryConfig { store?: MemoryStore }
 
+/** Test-only view of the coordinator containers whose retirement is the contract under test. */
+interface CoordinatorInternals {
+  states: Map<unknown, unknown>
+  buffers: Map<unknown, unknown>
+  chains: Map<unknown, unknown>
+  inits: Map<unknown, unknown>
+  retirements: Set<Promise<void>>
+}
+
 /**
  * Reference {@link PersistenceCoordinator} vehicle and abstract-service coverage, backed by a
  * dependency-free map with atomic writes and no torn-tail marker. Supplying the map lets multiple
@@ -41,6 +70,10 @@ class MemoryPersistence extends SessionPersistence implements PersistenceBackend
 
   // --- service surface (delegated to the coordinator) ---
 
+  locate(_meta: SessionHeader): undefined {
+    return undefined
+  }
+
   create(m: SessionHeader): Promise<void> {
     return this.coordinator.create(m)
   }
@@ -97,6 +130,49 @@ class MemoryPersistence extends SessionPersistence implements PersistenceBackend
   }
 }
 
+/** Controllable storage primitive for serialization and retirement failure tests. */
+class ControlledBackend implements PersistenceBackend<never> {
+  readonly name = 'session-persistence-controlled'
+  readonly store: MemoryStore = new Map()
+  readonly lifecycle: string[] = []
+  appendAttempts = 0
+  loadAttempts = 0
+  beforeAppend?: (attempt: number) => Promise<void>
+  beforeLoadStored?: (attempt: number) => Promise<void>
+
+  async loadStored(id: SessionId): Promise<StoredPrefix<never> | undefined> {
+    await this.beforeLoadStored?.(++this.loadAttempts)
+    const entry = this.store.get(id)
+    if (entry === undefined) return undefined
+    return { meta: structuredClone(entry.meta), events: structuredClone(entry.events) }
+  }
+
+  loadLive(id: SessionId, _cwd: string | undefined): Promise<StoredPrefix<never> | undefined> {
+    return this.loadStored(id)
+  }
+
+  async appendBatch(m: SessionHeader, events: readonly SessionEvent[], _isMaterialized: boolean): Promise<void> {
+    const attempt = ++this.appendAttempts
+    await this.beforeAppend?.(attempt)
+    const entry = this.store.get(m.id)
+    if (entry === undefined) {
+      this.store.set(m.id, { meta: structuredClone(m), events: structuredClone(events) as SessionEvent[] })
+    } else {
+      entry.events.push(...structuredClone(events) as SessionEvent[])
+    }
+  }
+
+  async commitRepair(_m: SessionHeader, _tornMarker: undefined, _closers: readonly SessionEvent[]): Promise<void> {}
+
+  async list(): Promise<SessionHeader[]> {
+    return [...this.store.values()].map(entry => structuredClone(entry.meta))
+  }
+
+  async close(): Promise<void> {
+    this.lifecycle.push('close')
+  }
+}
+
 // Run the shared contract against the in-memory backend.
 runPersistenceContract('memory', async () => {
   const ctx = new Context()
@@ -118,6 +194,230 @@ runCoordinatorContract('memory', async (): Promise<CoordinatorFixture> => {
   }
 })
 
+describe('PersistenceCoordinator retirement', () => {
+  it('a retiring unmaterialized owner without buffered events releases its id', async () => {
+    const ctx = new Context()
+    await ctx.plugin(SessionStore)
+    const backend = new ControlledBackend()
+    let coordinator!: PersistenceCoordinator<never>
+    const backendFiber = await ctx.plugin(Object.assign((inner: Context) => {
+      coordinator = new PersistenceCoordinator(inner, backend)
+    }, { inject: ['sessions'] }))
+    const loadGate = Promise.withResolvers<boolean>()
+
+    try {
+      const id = SessionId('retiring-lazy-owner')
+      let first!: Session
+      const firstFiber = await ctx.plugin(Object.assign((inner: Context) => {
+        first = inner.sessions.create(id)
+      }, { inject: ['sessions'] }))
+      await ctx.sessions.flush(first)
+
+      const baselineLoads = backend.loadAttempts
+      backend.beforeLoadStored = async () => { await loadGate.promise }
+      const blockingLoad = coordinator.load(id)
+      await vi.waitFor(() => { expect(backend.loadAttempts).toBe(baselineLoads + 1) })
+      await firstFiber.dispose()
+
+      let reuse!: Session
+      await ctx.plugin(Object.assign((inner: Context) => {
+        reuse = inner.sessions.create(id)
+      }, { inject: ['sessions'] }))
+      await vi.waitFor(() => { expect(backend.loadAttempts).toBe(baselineLoads + 2) })
+
+      loadGate.resolve(true)
+      await expect(blockingLoad).rejects.toThrow(/not found/)
+      await expect(ctx.sessions.flush(reuse)).resolves.toBeUndefined()
+    } finally {
+      loadGate.resolve(true)
+      await backendFiber.dispose()
+      await ctx.fiber.dispose()
+    }
+  })
+
+  it('a retiring owner with buffered events still rejects same-id reuse', async () => {
+    const ctx = new Context()
+    await ctx.plugin(SessionStore)
+    const backend = new ControlledBackend()
+    let coordinator!: PersistenceCoordinator<never>
+    const backendFiber = await ctx.plugin(Object.assign((inner: Context) => {
+      coordinator = new PersistenceCoordinator(inner, backend)
+    }, { inject: ['sessions'] }))
+    const loadGate = Promise.withResolvers<boolean>()
+
+    try {
+      const id = SessionId('retiring-buffered-owner')
+      let first!: Session
+      const firstFiber = await ctx.plugin(Object.assign((inner: Context) => {
+        first = inner.sessions.create(id)
+      }, { inject: ['sessions'] }))
+      await ctx.sessions.flush(first)
+      first.append('turn/start', { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } })
+      first.append('turn/end', { turn: 1, reason: { kind: 'completed' } })
+
+      const baselineLoads = backend.loadAttempts
+      backend.beforeLoadStored = async () => { await loadGate.promise }
+      const blockingLoad = coordinator.load(id)
+      await vi.waitFor(() => { expect(backend.loadAttempts).toBe(baselineLoads + 1) })
+      await firstFiber.dispose()
+
+      let reuse!: Session
+      await ctx.plugin(Object.assign((inner: Context) => {
+        reuse = inner.sessions.create(id)
+      }, { inject: ['sessions'] }))
+      await expect(ctx.sessions.flush(reuse)).rejects.toThrow(/bound to a different live session/)
+
+      loadGate.resolve(true)
+      await expect(blockingLoad).rejects.toThrow(/not found/)
+      await vi.waitFor(() => {
+        expect(backend.store.get(id)?.events.map(event => event.seq)).toEqual([0, 1])
+      })
+    } finally {
+      loadGate.resolve(true)
+      await backendFiber.dispose()
+      await ctx.fiber.dispose()
+    }
+  })
+
+  it('a settled chain tail cannot delete a newer operation for the same id', async () => {
+    const ctx = new Context()
+    await ctx.plugin(SessionStore)
+    const backend = new ControlledBackend()
+    let coordinator!: PersistenceCoordinator<never>
+    const fiber = await ctx.plugin(Object.assign((inner: Context) => {
+      coordinator = new PersistenceCoordinator(inner, backend)
+    }, { inject: ['sessions'] }))
+    const internals = coordinator as unknown as CoordinatorInternals
+    const first = Promise.withResolvers<boolean>()
+    const second = Promise.withResolvers<boolean>()
+    backend.beforeAppend = async (attempt) => {
+      if (attempt === 1) await first.promise
+      if (attempt === 2) await second.promise
+    }
+
+    try {
+      const id = SessionId('chain-tail')
+      await coordinator.create(meta(id))
+      const firstAppend = coordinator.append(id, [{
+        type: 'turn/start',
+        seq: 0,
+        time: 1,
+        data: { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } },
+      }])
+      const secondAppend = coordinator.append(id, [{
+        type: 'turn/end',
+        seq: 1,
+        time: 2,
+        data: { turn: 1, reason: { kind: 'completed' } },
+      }])
+
+      await vi.waitFor(() => { expect(backend.appendAttempts).toBe(1) })
+      first.resolve(true)
+      await vi.waitFor(() => { expect(backend.appendAttempts).toBe(2) })
+      expect(internals.chains.size).toBe(1)
+      second.resolve(true)
+      await Promise.all([firstAppend, secondAppend])
+      await vi.waitFor(() => { expect(internals.chains.size).toBe(0) })
+      expect(backend.store.get(id)?.events.map(event => event.seq)).toEqual([0, 1])
+    } finally {
+      first.resolve(true)
+      second.resolve(true)
+      await fiber.dispose()
+      await ctx.fiber.dispose()
+    }
+  })
+
+  it('backend teardown retries a failed session retirement before close', async () => {
+    const ctx = new Context()
+    await ctx.plugin(SessionStore)
+    const backend = new ControlledBackend()
+    let coordinator!: PersistenceCoordinator<never>
+    const backendFiber = await ctx.plugin(Object.assign((inner: Context) => {
+      coordinator = new PersistenceCoordinator(inner, backend)
+    }, { inject: ['sessions'] }))
+    const internals = coordinator as unknown as CoordinatorInternals
+    backend.beforeAppend = async (attempt) => {
+      if (attempt === 1) {
+        backend.lifecycle.push('append-failed')
+        throw new Error('transient append failure')
+      }
+      backend.lifecycle.push('append-committed')
+    }
+
+    try {
+      let session!: Session
+      const sessionFiber = await ctx.plugin(Object.assign((inner: Context) => {
+        session = inner.sessions.create(SessionId('retry-retirement'))
+      }, { inject: ['sessions'] }))
+      session.append('turn/start', { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } })
+      session.append('turn/end', { turn: 1, reason: { kind: 'completed' } })
+      await sessionFiber.dispose()
+
+      await vi.waitFor(() => {
+        expect(backend.appendAttempts).toBe(1)
+        expect(internals.retirements.size).toBe(0)
+      })
+      expect([...internals.buffers.values()]).toEqual([expect.arrayContaining([
+        expect.objectContaining({ seq: 0 }),
+        expect.objectContaining({ seq: 1 }),
+      ])])
+
+      await backendFiber.dispose()
+      expect(backend.store.get(SessionId('retry-retirement'))?.events.map(event => event.seq)).toEqual([0, 1])
+      expect(backend.lifecycle).toEqual(['append-failed', 'append-committed', 'close'])
+    } finally {
+      await backendFiber.dispose()
+      await ctx.fiber.dispose()
+    }
+  })
+
+  it('backend teardown waits for an in-flight session retirement before close', async () => {
+    const ctx = new Context()
+    await ctx.plugin(SessionStore)
+    const backend = new ControlledBackend()
+    let coordinator!: PersistenceCoordinator<never>
+    const backendFiber = await ctx.plugin(Object.assign((inner: Context) => {
+      coordinator = new PersistenceCoordinator(inner, backend)
+    }, { inject: ['sessions'] }))
+    const internals = coordinator as unknown as CoordinatorInternals
+    const appendGate = Promise.withResolvers<boolean>()
+    backend.beforeAppend = async () => {
+      backend.lifecycle.push('append-started')
+      await appendGate.promise
+      backend.lifecycle.push('append-committed')
+    }
+
+    try {
+      let session!: Session
+      const sessionFiber = await ctx.plugin(Object.assign((inner: Context) => {
+        session = inner.sessions.create(SessionId('inflight-retirement'))
+      }, { inject: ['sessions'] }))
+      session.append('turn/start', { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } })
+      session.append('turn/end', { turn: 1, reason: { kind: 'completed' } })
+      await sessionFiber.dispose()
+      await vi.waitFor(() => {
+        expect(backend.appendAttempts).toBe(1)
+        expect(internals.retirements.size).toBe(1)
+      })
+
+      let disposed = false
+      const teardown = backendFiber.dispose().then(() => { disposed = true })
+      await Promise.resolve()
+      expect(disposed).toBe(false)
+      expect(backend.lifecycle).toEqual(['append-started'])
+
+      appendGate.resolve(true)
+      await teardown
+      expect(backend.store.get(SessionId('inflight-retirement'))?.events.map(event => event.seq)).toEqual([0, 1])
+      expect(backend.lifecycle).toEqual(['append-started', 'append-committed', 'close'])
+    } finally {
+      appendGate.resolve(true)
+      await backendFiber.dispose()
+      await ctx.fiber.dispose()
+    }
+  })
+})
+
 describe('SessionPersistence service registration', () => {
   it('registers as ctx.sessionPersistence and is removed on fiber dispose (HMR safety)', async () => {
     const ctx = new Context()
@@ -151,4 +451,95 @@ describe('SessionPersistence service registration', () => {
       .rejects.toThrow('session metadata must be losslessly JSON-serializable')
     await fiber.dispose()
   })
+
+  it('rejects a legacy header delta from a pre-change live producer', async () => {
+    const ctx = new Context()
+    await ctx.plugin(SessionStore)
+    const fiber = await ctx.plugin(MemoryPersistence)
+    const session = ctx.sessions.create(SessionId('legacy-live'), { meta: { cwd: '/legacy' } })
+    // Model the runtime shape available to JavaScript or a hot-loaded plugin
+    // compiled against the obsolete event vocabulary.
+    const appendLegacy = session.append.bind(session) as (type: string, data: unknown) => SessionEvent
+    expect(() => appendLegacy('request/header-delta', { config: { model: 'legacy' } }))
+      .toThrow(/unsupported legacy request\/header-delta format/)
+    expect(session.events).toHaveLength(0)
+    await fiber.dispose()
+  })
+
+  it('rejects a legacy fallback header buffered by a pre-change live producer', async () => {
+    const ctx = new Context()
+    await ctx.plugin(SessionStore)
+    const fiber = await ctx.plugin(MemoryPersistence)
+    const session = ctx.sessions.create(SessionId('legacy-fallback-live'), { meta: { cwd: '/legacy' } })
+    const appendLegacy = session.append.bind(session) as (type: string, data: unknown) => SessionEvent
+
+    expect(() => appendLegacy('request/header', legacyFallbackHeader().data))
+      .toThrow('unsupported legacy request/header reason "fallback"')
+    expect(session.events).toHaveLength(0)
+    await fiber.dispose()
+  })
+
+  it('rejects a legacy stored prefix during live HMR adoption', async () => {
+    const id = SessionId('legacy-hmr')
+    const m = meta(id, '/legacy')
+    const legacy = legacyHeaderDelta()
+    const store: MemoryStore = new Map([[id, { meta: m, events: [legacy] }]])
+    const ctx = new Context()
+    await ctx.plugin(SessionStore)
+    // A current live session cannot carry the obsolete event in its seed, but
+    // HMR still has to identify the persisted prefix as unsupported rather than
+    // treating it as an ordinary live-prefix collision.
+    const session = ctx.sessions.create(id, { meta: { cwd: '/legacy' } })
+    const fiber = await ctx.plugin(MemoryPersistence, { store })
+
+    await expect(ctx.sessions.flush(session))
+      .rejects.toThrow(/unsupported legacy request\/header-delta event at seq 0/)
+    await Promise.allSettled([fiber.dispose()])
+  })
+
+  it('rejects a stored legacy fallback header during load', async () => {
+    const id = SessionId('legacy-fallback-load')
+    const m = meta(id, '/legacy')
+    const store: MemoryStore = new Map([[id, { meta: m, events: [legacyFallbackHeader()] }]])
+    const ctx = new Context()
+    await ctx.plugin(SessionStore)
+    const fiber = await ctx.plugin(MemoryPersistence, { store })
+
+    await expect(ctx.sessionPersistence.load(id))
+      .rejects.toThrow('unsupported legacy request/header reason "fallback" at seq 0')
+    await fiber.dispose()
+  })
+
+  it('retires all coordinator bookkeeping for disposed sessions', async () => {
+    const ctx = new Context()
+    await ctx.plugin(SessionStore)
+    const fiber = await ctx.plugin(MemoryPersistence)
+    const { coordinator } = ctx.sessionPersistence as unknown as { coordinator: CoordinatorInternals }
+
+    try {
+      for (let index = 0; index < 3; index += 1) {
+        let session!: Session
+        const sessionFiber = await ctx.plugin(Object.assign((inner: Context) => {
+          session = inner.sessions.create(SessionId(`disposed-${index}`))
+        }, { inject: ['sessions'] }))
+        session.append('turn/start', { turn: 1, trigger: { kind: 'message', source: { kind: 'user' } } })
+        session.append('turn/end', { turn: 1, reason: { kind: 'completed' } })
+        await ctx.sessions.flush(session)
+        await sessionFiber.dispose()
+      }
+
+      await vi.waitFor(() => {
+        expect(ctx.sessions.list()).toHaveLength(0)
+        expect({
+          states: coordinator.states.size,
+          buffers: coordinator.buffers.size,
+          chains: coordinator.chains.size,
+          inits: coordinator.inits.size,
+          retirements: coordinator.retirements.size,
+        }).toEqual({ states: 0, buffers: 0, chains: 0, inits: 0, retirements: 0 })
+      })
+    } finally {
+      await fiber.dispose()
+    }
+  })
 })