feat: add native macOS desktop app

docs/issues/subagent-session-stays-starting.md

@@ -0,0 +1,7 @@
+# Subagent session can stay in `starting` indefinitely
+
+While implementing the macOS desktop app with Kit 0.1.86, a final review subagent remained in `starting` and never accepted work. Closing completed sibling sessions did not unblock it. Cancelling that session and creating a fresh subagent produced the same behavior.
+
+This creates friction because `subagents` provides no failure reason or timeout for the stuck startup, so the parent cannot distinguish queueing from a failed harness launch. The parent must abandon the review or repeatedly cancel and retry.
+
+Expected behavior: a subagent either starts within a bounded interval or transitions to a failed state with a diagnostic that explains the capacity or harness problem.

fixtures/mock-acp.py

@@ -1,5 +1,7 @@
 #!/usr/bin/env python3
 import json
+import os
+import subprocess
 import sys
 import threading
 import time
@@ -11,6 +13,11 @@
 selected_models = {}
 model_ids = ["mock/default", "mock/requested"]
 
+if os.environ.get("MOCK_CHILD_PID_FILE"):
+    child = subprocess.Popen([sys.executable, "-c", "import signal,time; signal.signal(signal.SIGTERM, signal.SIG_IGN); time.sleep(60)"] )
+    with open(os.environ["MOCK_CHILD_PID_FILE"], "w") as file:
+        file.write(str(child.pid))
+
 
 def send(message):
     with write_lock:
@@ -25,12 +32,16 @@ def respond(request_id, result):
 def prompt(request):
     params = request["params"]
     session_id = params["sessionId"]
-    text = params["prompt"][0]["text"]
+    text = next((block.get("text", "") for block in params["prompt"] if block.get("type") == "text"), "")
+    if "MOCK_HANG" in text:
+        return
     time.sleep(0.40)
     if "MOCK_SELECTED_MODEL" in text:
         text = selected_models.get(session_id, model_ids[0])
     if "MOCK_STRUCTURED_OUTPUT" in text:
         text = json.dumps({"approved": True, "reason": "mock approved"})
+    if "MOCK_MEDIA" in text:
+        text = ",".join(block.get("type", "unknown") for block in params["prompt"])
     if "MOCK_RICH_OUTPUT" in text:
         updates = [
             {
@@ -69,6 +80,12 @@ def prompt(request):
                 "method": "session/update",
                 "params": {"sessionId": session_id, "update": update},
             })
+            if update["sessionUpdate"] == "tool_call":
+                sys.stderr.write("\x01kit-runtime\x01" + json.dumps({"event": "child_started", "call": "call-1:compose:shell", "tool": "shell", "summary": "echo mock", "at": 1}) + "\n")
+                sys.stderr.flush()
+            elif update["sessionUpdate"] == "tool_call_update":
+                sys.stderr.write("\x01kit-runtime\x01" + json.dumps({"event": "child_finished", "call": "call-1:compose:shell", "tool": "shell", "ok": True, "summary": "done", "millis": 2}) + "\nmock diagnostic\n")
+                sys.stderr.flush()
         text = "rich done"
     send({
         "jsonrpc": "2.0",
@@ -99,6 +116,10 @@ def prompt(request):
     elif method == "session/new":
         selected_models["base"] = model_ids[0]
         result = {"sessionId": "base"}
+        if os.environ.get("MOCK_EXIT_TAIL"):
+            sys.stdout.write(json.dumps({"jsonrpc": "2.0", "id": request["id"], "result": result}))
+            sys.stdout.flush()
+            os._exit(0)
         if supports_models:
             result["configOptions"] = [{
                 "id": "model",
@@ -111,6 +132,31 @@ def prompt(request):
                 ],
             }]
         respond(request["id"], result)
+        send({"jsonrpc": "2.0", "method": "session/update", "params": {
+            "sessionId": result["sessionId"],
+            "update": {"sessionUpdate": "available_commands_update", "availableCommands": [
+                {"name": "compact", "description": "Compact the session context"}
+            ]},
+        }})
+    elif method == "session/load":
+        session_id = request["params"]["sessionId"]
+        selected_models[session_id] = model_ids[0]
+        for update in [
+            {"sessionUpdate": "user_message_chunk", "content": {"type": "text", "text": "replayed user"}},
+            {"sessionUpdate": "agent_message_chunk", "content": {"type": "text", "text": "replayed assistant"}},
+        ]:
+            send({"jsonrpc": "2.0", "method": "session/update", "params": {"sessionId": session_id, "update": update}})
+        result = {}
+        if supports_models:
+            result["configOptions"] = [{
+                "id": "model", "name": "Model", "category": "model", "type": "select",
+                "currentValue": model_ids[0], "options": [{"value": value, "name": value} for value in model_ids],
+            }]
+        respond(request["id"], result)
+        send({"jsonrpc": "2.0", "method": "session/update", "params": {
+            "sessionId": session_id,
+            "update": {"sessionUpdate": "available_commands_update", "availableCommands": [{"name": "compact", "description": "Compact the session context"}]},
+        }})
     elif method == "session/fork":
         if not supports_fork:
             send({

macos/.gitignore

@@ -0,0 +1,3 @@
+.build/
+*.xcuserstate
+xcuserdata/