fix(server): stream a prompt Pi queued after the server turn ended

[oxwen11]

Requirement

A follow-up sent while Pi still considered itself streaming, after Pie had already closed the turn, failed with Pi queued a prompt without an active server turn. The UI froze. Pi kept running the prompt with nobody listening.

Expected behavior

• A prompt Pi queues while Pie has no active turn is streamed as a new turn, not rejected.
• A prompt Pi reports as handled still does not open a turn.
• A follow-up queued onto a turn Pie is already streaming stays attached to that turn.

Changes and risks

packages/server prompt admission. The Pi RPC response now includes disposition. No stored-data or wire-contract change for clients. An old child that omits disposition and returns started: false while idle is treated as queued and streamed.

Verification

• Revision: 919aa344
• pnpm exec vitest run test/harness/pi/agent.test.ts in packages/server: 24 passed.
• Not verified against a live Pie.app or a real model turn.

[pkg-pr-new]

npx https://pkg.pr.new/oxwen11/pie/@getpie/cli@429

commit: 919aa34

[oxwen11]

auto-merge: no

head: 919aa344e24debae39eea95a0824bbf2cc69dbb2

Fail closed on exclusions + no matching allowed group:

• non-presentational fix: packages/server/src/harness/pi/process.ts changes prompt-admission control flow (handled/queued idle path instead of AgentOperationError).
• RPC/schema/wire: rpc-mode.ts / rpc-types.ts add disposition on prompt success data (started | queued | handled).
• Tests in agent.test.ts cover the new product control flow — not an allowed group.

Din review-first; no merge.