simplify(seams): prune dead methods from the persistence and bash seams

Two capability seams carried abstract methods no production consumer calls.
A method no consumer programs against is not a seam — it is speculative
surface every implementation must still provide and test.

- SessionPersistence: remove has() and delete(), the coordinator's
  has/delete/deleteCore, and the PersistenceBackend.deleteStored hook (with its
  jsonl + sqlite + in-spec memory-stub impls). Surviving service surface:
  create/append/load/list. Production uses only load() (resume) and list()
  (ACP session/list).
- BashExecutor: remove get(id) and list(), the abstract decls and the
  LocalBashExecutor impls. The internal tasks map survives (it backs
  ownerOf/readOutput/kill); get/list were pure public accessors over it with no
  shipping caller and no bash_list tool.
- Migrate tests that reached through ctx.bash.get(id) to the public completion
  seam: a doneFor(id) helper over onTaskDone awaits a task by id, and the
  HMR-reload ownership test now proves task survival through A's own bash_output
  ([status: running]) plus ownerOf + B-rejection — a stronger through-the-tool
  assertion than the removed lookup peek.
- Update seam READMEs (six -> four service methods, drop the deleteStored hook
  and the get/list row) and the two implemented persistence RFCs in place.

Implements docs/rfc/implemented/simplification/2026-06-20-prune-dead-seam-methods.md

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

@@ -142,24 +142,22 @@ export function runPersistenceContract(name: string, make: () => Promise<Contrac
       }
     })
 
-    it('has()/list() exclude a created-but-never-appended (zero-event) session', async () => {
+    it('list() excludes a created-but-never-appended (zero-event) session', async () => {
       const { persistence, dispose } = await make()
       try {
         await persistence.create(meta('empty'))
-        expect(await persistence.has(SessionId('empty'))).toBe(false)
         expect((await persistence.list()).map(m => m.id)).not.toContain(SessionId('empty'))
       } finally {
         await dispose()
       }
     })
 
-    it('has()/list() include a session once it has events', async () => {
+    it('list() includes a session once it has events', async () => {
       const { persistence, dispose } = await make()
       try {
         const m = meta('s2')
         await persistence.create(m)
         await persistence.append(m.id, oneTurnLog())
-        expect(await persistence.has(m.id)).toBe(true)
         expect((await persistence.list()).map(x => x.id)).toContain(m.id)
       } finally {
         await dispose()
@@ -227,19 +225,5 @@ export function runPersistenceContract(name: string, make: () => Promise<Contrac
         await dispose()
       }
     })
-
-    it('delete removes a session', async () => {
-      const { persistence, dispose } = await make()
-      try {
-        const m = meta('s6')
-        await persistence.create(m)
-        await persistence.append(m.id, oneTurnLog())
-        expect(await persistence.has(m.id)).toBe(true)
-        await persistence.delete(m.id)
-        expect(await persistence.has(m.id)).toBe(false)
-      } finally {
-        await dispose()
-      }
-    })
   })
 }

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

@@ -625,7 +625,7 @@ export function runCoordinatorContract(name: string, makeFixture: () => Promise<
         const m = meta('empty-batch', WORK)
         await ctx.sessionPersistence.create(m)
         await ctx.sessionPersistence.append(m.id, [])
-        expect(await ctx.sessionPersistence.has(m.id)).toBe(false)
+        expect((await ctx.sessionPersistence.list()).map(h => h.id)).not.toContain(m.id)
       } finally {
         await fiber.dispose()
         await fix.cleanup()
@@ -643,17 +643,6 @@ export function runCoordinatorContract(name: string, makeFixture: () => Promise<
       }
     })
 
-    it('delete of a non-existent session is a no-op', async () => {
-      const fix = await makeFixture()
-      const { ctx, fiber } = await freshCtx(fix)
-      try {
-        await expect(ctx.sessionPersistence.delete(SessionId('ghost'))).resolves.toBeUndefined()
-      } finally {
-        await fiber.dispose()
-        await fix.cleanup()
-      }
-    })
-
     it('create rejects a duplicate id (in memory and on a persisted log)', async () => {
       const fix = await makeFixture()
       const first = await freshCtx(fix)

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

@@ -61,14 +61,6 @@ class MemoryPersistence extends SessionPersistence implements PersistenceBackend
     return this.coordinator.load(id)
   }
 
-  has(id: SessionId): Promise<boolean> {
-    return this.coordinator.has(id)
-  }
-
-  delete(id: SessionId): Promise<void> {
-    return this.coordinator.delete(id)
-  }
-
   /** White-box accessor: await a specific session's onCreated init. */
   get inits(): Map<Session, Promise<void>> {
     return this.coordinator.inits
@@ -114,10 +106,6 @@ class MemoryPersistence extends SessionPersistence implements PersistenceBackend
     if (closers.length > 0) entry.events.push(...structuredClone(closers) as SessionEvent[])
   }
 
-  async deleteStored(id: SessionId): Promise<void> {
-    this.store.delete(id)
-  }
-
   async list(): Promise<SessionHeader[]> {
     return [...this.store.values()].map(e => structuredClone(e.meta))
   }