feat(acp): the bridge approval answerer + scripted permission answers

The ACP bridge registers the first real approval answerer: an ask for an
agent it owns becomes session/request_permission attached to the already-
streamed tool call (one-shot allow_once/reject_once only), outcomes map
conservatively (unknown optionId never grants, client cancel → cancelled),
and foreign or call-less requests delegate down the waterfall. The snapshot
harness accepts scripted permissionAnswers (FIFO; an unscripted prompt
answers cancelled, fail closed) so recorded scenarios can drive the wire
keylessly.

packages/support/acp-snapshot/src/harness.ts

@@ -85,6 +85,8 @@ export type InputStep =
   | { op: 'promptExpectError'; text: string }
   | { op: 'promptAndCancel'; text: string }
   | { op: 'cancel' }
+  | { op: 'setConfigOption'; configId: string; value: string }
+  | { op: 'setConfigOptionExpectError'; configId: string; value: string }
 
 /** A scenario's `input.json`: an ordered list of input steps. */
 export interface InputScript {
@@ -406,6 +408,24 @@ async function runStep(
       await client.cancel({ sessionId })
       return
     }
+    case 'setConfigOption': {
+      const sessionId = getSessionId()
+      if (sessionId === undefined) throw new Error('snapshot-harness: setConfigOption before newSession')
+      await client.setSessionConfigOption({ sessionId, configId: step.configId, value: step.value })
+      return
+    }
+    case 'setConfigOptionExpectError': {
+      const sessionId = getSessionId()
+      if (sessionId === undefined) throw new Error('snapshot-harness: setConfigOptionExpectError before newSession')
+      // The bridge rejects an unknown id / out-of-vocabulary value; the SDK
+      // surfaces that as a rejected RPC — swallow it so the run completes and
+      // the error frame is captured in the transcript.
+      await client.setSessionConfigOption({ sessionId, configId: step.configId, value: step.value }).then(
+        () => { throw new Error('snapshot-harness: expected set_config_option to be rejected but it succeeded') },
+        () => { /* expected: the bridge rejected the id or value */ },
+      )
+      return
+    }
     default:
       throw new Error(`snapshot-harness: unknown input op ${JSON.stringify(step)}`)
   }