Rewind chat or files from any user message (#1154)

* Add Pi extension-launch plumbing for in-process tree primitives

* Add Rewind controls for agent sessions

* Preserve SDK checkpoint env var so Claude file rewind works

The SDK injects CLAUDE_CODE_ENABLE_SDK_FILE_CHECKPOINTING=true when file checkpointing is enabled. The earlier parent-env stripping from c4782ec71c was too broad and removed that child flag along with real parent-session markers.

Keep stripping parent markers, but preserve the checkpoint flag so the SDK rewind path can run directly. With that boundary fixed, the JSONL file-rewind fallback is no longer needed.

* Update OpenCode history replay tests for rewind state

* Show Rewind actions in an adaptive sheet

* Fix rewind semantics across providers

* Refactor Pi IDs through extension capture

* Restore user message to composer after rewind

* Fix Claude rewind tool result mapping

* Fix Claude rewind session switch roundtrip

* Fix rewind and optimistic message regressions

* Tighten rewind test discipline

* Fix OpenCode optimistic message reconciliation

* Reconcile optimistic user messages by marker

* Reorder user message actions

* Unify provider user message contract

* Add Claude rewind flow Playwright contract

* Add Codex rewind flow Playwright contract

* Add OpenCode rewind flow Playwright contract

* Add Pi rewind flow Playwright contract

* Remove real-provider rewind Playwright contracts

* Gate real-provider rewind specs from CI Playwright

packages/app/src/hooks/use-agent-screen-state-machine.ts

@@ -1,10 +1,12 @@
 import { useRef } from "react";
+import type { AgentCapabilityFlags } from "@server/server/agent/agent-sdk-types";
 
 export interface AgentScreenAgent {
   serverId: string;
   id: string;
   status: "initializing" | "idle" | "running" | "error" | "closed";
   cwd: string;
+  capabilities?: AgentCapabilityFlags;
   lastError?: string | null;
   projectPlacement?: {
     checkout?: {