fix(acp-registry): ACP v2 agent prompt handling + state updates

apps/server/src/orchestration-v2/Adapters/AcpRegistryAdapterV2.test.ts

@@ -1949,6 +1949,79 @@ describe("AcpRegistryAdapterV2", () => {
     }).pipe(Effect.provide(layerTest), Effect.scoped),
   );
 
+  it.effect("follows the work state of any agent that negotiates ACP v2", () =>
+    Effect.gen(function* () {
+      const gate = makeProviderReplayGate(["elsewhere"]);
+      const { update, idle, prompt } = claudeFrames;
+      const reply = (messageId: string, text: string) =>
+        update(CLAUDE_ROOT_SESSION, {
+          sessionUpdate: "agent_message_chunk",
+          messageId,
+          content: { type: "text", text },
+        });
+      const session = yield* openClaudeReplaySession(
+        [
+          ...claudeFrames.open,
+          ...prompt(1),
+          reply("reply-1", "Working on it."),
+          idle("end_turn"),
+          claudeMarker("foreground idle"),
+          {
+            ...update(CLAUDE_ROOT_SESSION, {
+              sessionUpdate: "user_message",
+              messageId: "elsewhere-1",
+              content: [{ type: "text", text: "Sent from another client" }],
+            }),
+            label: "elsewhere",
+          },
+          update(CLAUDE_ROOT_SESSION, { sessionUpdate: "state_update", state: "running" }),
+          reply("reply-2", "Answered elsewhere."),
+          idle("end_turn"),
+          claudeMarker("elsewhere idle"),
+        ],
+        gate,
+        true,
+        "fixture-agent",
+      );
+      yield* session.runtime.startTurn(session.turnInput(1));
+      const foreground = yield* session.until((event) => event.type === "turn.terminal");
+      const terminal = foreground.at(-1)!;
+      if (terminal.type !== "turn.terminal") throw new Error("Missing terminal");
+      assert.equal(terminal.status, "completed");
+      assert.isTrue(
+        foreground.some(
+          (event) => event.type === "message.updated" && event.message.text === "Working on it.",
+        ),
+        "an accepted prompt is not the end of the turn; idle is",
+      );
+      assert.isFalse(
+        foreground.some(
+          (event) => event.type === "message.updated" && event.message.text === "test prompt",
+        ),
+        "the agent's echo of the submitted prompt only signals acceptance",
+      );
+      yield* session.throughMarker("foreground idle");
+
+      gate.release("elsewhere");
+      yield* Queue.take(session.offered);
+      yield* session.throughMarker("elsewhere idle");
+      assert.lengthOf(session.offers, 1);
+      yield* session.offers[0]!.dispatchIfCurrent!(Effect.void);
+      yield* session.runtime.startTurn(session.turnInput(2, { continuation: true }));
+      const continuation = yield* session.until((event) => event.type === "turn.terminal");
+      const continued = continuation.at(-1)!;
+      if (continued.type !== "turn.terminal") throw new Error("Missing continuation terminal");
+      assert.equal(continued.status, "completed");
+      assert.isTrue(
+        continuation.some(
+          (event) =>
+            event.type === "message.updated" && event.message.text === "Answered elsewhere.",
+        ),
+        "work the agent started on its own reaches the thread",
+      );
+    }).pipe(Effect.provide(layerTest), Effect.scoped),
+  );
+
   it.effect("keeps stopped child tools interrupted when a late output chunk arrives", () =>
     Effect.gen(function* () {
       const { update } = claudeFrames;

docs/user/providers-acp.md

@@ -12,7 +12,9 @@ Pi, and [Antigravity](./providers-antigravity.md), don't appear in the Registry
 T3 Code prefers the current ACP v2 preview protocol and uses its richer messages, usage, plans,
 configuration, compaction, and agent-terminal updates when the agent supports them. It also
 negotiates ACP v1 for Registry agents that have not migrated yet, so they continue to work through
-the same generic integration.
+the same generic integration. On ACP v2, T3 Code follows the agent's reported work state: a turn
+ends when the agent goes idle, and work the agent starts on its own, such as answering a message
+sent from another client, appears in the thread.
 
 Claude Agent uses the ACP v2 preview by default for Registry and local `claude-agent-acp`
 commands. If you encounter preview issues, set `CLAUDE_AGENT_ACP_EXPERIMENTAL_V2=0` in the

packages/provider-acp-registry/src/server/adapter.ts

@@ -228,9 +228,11 @@ export const makeAcpRegistryAdapterV2 = Effect.fn("makeAcpRegistryAdapterV2")(fu
     ...(registryAgentId === "mistral-vibe"
       ? { registerExtensions: registerMistralVibeAcpExtensions }
       : {}),
+    // ACP v2 reports turn completion, and work the agent starts on its own, through
+    // `state_update`; the adapter follows it only once an agent negotiates v2.
+    followAgentWorkState: true,
     ...(isClaude
       ? {
-          followAgentWorkState: true,
           extractSubagentUpdate: extractClaudeSubagentUpdate,
           isProvisionalSubagentTool: isClaudeProvisionalSubagentTool,
           extractSubagentSessionEvent: extractClaudeSubagentSessionEvent,