refactor(web): drop the permission RPC pair and turn-anchoring machinery

The session.permissions/setPermission unary pair, the PermissionOption wire
DTO, the client Session wrappers, and the fixture/fake mirrors all leave the
wire: the read side moves to the 'permissions' session projection and the
write side moves to the /permission command in follow-up commits, so the
web protocol gains no permission methods at all.

The pendingSwitches + prompt-submit flush + hasOpenTurn move also goes.
Knob events no longer need turn enclosure: the persistence scanner keeps
standalone events after the last turn/end as part of the preserved prefix
(remove-synthetic-log-only-turns), none of the three knob invariants demand
an open turn, and the setters append bare events. An idle switch commits
immediately; hasOpenTurn stays a user-approval private fold (its audit pair
is the one contract that still requires enclosure).

The old PermissionSelect chip and its mount-time fetch die with the RPCs
(the resident composer broke the mount-once assumption); the projection-fed
replacement lands with the Access seat swap.

packages/client/runtime/tests/fake-api.ts

@@ -81,12 +81,6 @@ export class FakeApiClient implements IApiClient {
     payload => Promise.resolve(ok({ selected: { provider: payload.provider, model: payload.model } }))
   onPrompt: (payload: unknown) => Promise<RpcResponse<{ accepted: true }>> = () => Promise.resolve(ok({ accepted: true as const }))
   onCancel: (payload: unknown) => Promise<RpcResponse<{ accepted: true }>> = () => Promise.resolve(ok({ accepted: true as const }))
-  onPermissions: (payload: unknown) =>
-  Promise<RpcResponse<{ options: { value: string; name: string; description?: string }[]; currentValue: string }>> =
-    () => Promise.resolve(ok({ options: [], currentValue: 'custom' }))
-
-  onSetPermission: (payload: { sessionId: SessionId; value: string }) => Promise<RpcResponse<{ currentValue: string }>> =
-    payload => Promise.resolve(ok({ currentValue: payload.value }))
 
   onDescribe: (payload: unknown) => Promise<RpcResponse<{ version: string; cwd: string; attachedSessions: number }>> =
     () => Promise.resolve(ok({ version: '0-fake', cwd: '/f', attachedSessions: 0 }))
@@ -111,8 +105,6 @@ export class FakeApiClient implements IApiClient {
       this.record('session.selectModel', payload, this.onSelectModel(payload)),
     prompt: (payload: unknown) => this.record('session.prompt', payload, this.onPrompt(payload)),
     cancel: (payload: unknown) => this.record('session.cancel', payload, this.onCancel(payload)),
-    permissions: (payload: unknown) => this.record('session.permissions', payload, this.onPermissions(payload)),
-    setPermission: (payload: { sessionId: SessionId; value: string }) => this.record('session.setPermission', payload, this.onSetPermission(payload)),
   }
 
   readonly host: IApiClient['host'] = {