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.test.ts

@@ -99,6 +99,16 @@ function expectSyncErrorSync(state: ReadyState): void {
   expect(state.sync.status).toBe("sync_error");
 }
 
+function stateMachineLabel(state: AgentScreenViewState): "loading" | "resolving" | Agent["status"] {
+  if (state.tag === "boot") {
+    return state.reason;
+  }
+  if (state.tag === "ready") {
+    return state.agent.status;
+  }
+  return "error";
+}
+
 describe("deriveAgentScreenViewState", () => {
   it("returns boot loading before first interactive paint", () => {
     const memory = createBaseMemory();
@@ -383,6 +393,39 @@ describe("deriveAgentScreenViewState", () => {
     expect(ready.agent.status).toBe("running");
   });
 
+  it("keeps send lifecycle transitions forward-only across optimistic and authoritative handoff", () => {
+    let memory = createBaseMemory();
+    const transitions: Array<"loading" | "resolving" | Agent["status"]> = [];
+
+    for (const input of [
+      createBaseInput(),
+      {
+        ...createBaseInput(),
+        agent: createAgentWithStatus({ id: "agent-1", status: "idle" }),
+        placeholderAgent: createAgent("agent-1"),
+        shouldUseOptimisticStream: true,
+      },
+      {
+        ...createBaseInput(),
+        agent: createAgentWithStatus({ id: "agent-1", status: "running" }),
+        placeholderAgent: createAgent("agent-1"),
+        shouldUseOptimisticStream: true,
+      },
+      {
+        ...createBaseInput(),
+        agent: createAgentWithStatus({ id: "agent-1", status: "idle" }),
+      },
+    ] satisfies AgentScreenMachineInput[]) {
+      const result = deriveAgentScreenViewState({ input, memory });
+      memory = result.memory;
+      transitions.push(stateMachineLabel(result.state));
+    }
+
+    expect(transitions).toEqual(["loading", "running", "running", "idle"]);
+    expect(transitions.join(" -> ")).not.toContain("running -> loading");
+    expect(transitions.join(" -> ")).not.toContain("loading -> idle");
+  });
+
   it("keeps optimistic running status while authoritative agent is initializing", () => {
     const memory = createBaseMemory();
     const input: AgentScreenMachineInput = {