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/ui/user-approval/src/index.ts

@@ -11,7 +11,6 @@ import type { Agent } from '@deepseek-ai/dsh-agent'
 import { createUserMessage, type CallId } from '@deepseek-ai/dsh-llm'
 import { scopeTarget } from '@deepseek-ai/dsh-scope'
 import type { Scoped } from '@deepseek-ai/dsh-scope'
-import { hasOpenTurn } from '@deepseek-ai/dsh-session'
 import type { Session, SessionEvent } from '@deepseek-ai/dsh-session'
 import type {} from '@deepseek-ai/dsh-system-prompt'
 
@@ -139,6 +138,22 @@ export function effectiveApprovalPolicy(events: readonly SessionEvent[]): Approv
   return undefined
 }
 
+/**
+ * Whether the log currently sits inside an open turn (a `turn/start` not yet
+ * closed by a `turn/end`) — the {@link ApprovalService.request} precondition.
+ * The audit pair must be turn-enclosed: the turn is the durable log's
+ * commit/replay boundary, so a bare event appended between turns is
+ * indistinguishable from a crash tail and silently dropped on reload.
+ */
+function hasOpenTurn(events: readonly SessionEvent[]): boolean {
+  for (let index = events.length - 1; index >= 0; index -= 1) {
+    const type = (events[index] as SessionEvent).type
+    if (type === 'turn/start') return true
+    if (type === 'turn/end') return false
+  }
+  return false
+}
+
 /**
  * Append the sole durable representation of a session policy override. Invalid
  * values throw before the log changes; consumers fold the new value on each read.