fix(terminal): collapse CWD-only overrides to shared container

When register_task_env_overrides is called with only a 'cwd' key
(ACP adapter workspace tracking), the task_id should collapse to
'default' so all interactive surfaces (TUI, gateway, dashboard)
share one long-lived container.

Previously, any override registration — even CWD-only — caused
_resolve_container_task_id to return the session key unchanged,
spinning up a separate container per session. This made it
impossible to authenticate into external services once and have
that auth available across all surfaces.

Now only overrides containing isolation keys (docker_image,
modal_image, singularity_image, daytona_image, env_type) trigger
per-task container isolation.

Fixes #37361

tests/tools/test_shared_container_task_id.py

@@ -105,3 +105,49 @@ def test_get_active_env_honours_rl_override():
         terminal_tool.clear_task_env_overrides("rl-42")
         terminal_tool._active_environments.pop("default", None)
         terminal_tool._active_environments.pop("rl-42", None)
+
+
+def test_cwd_only_override_collapses_to_default():
+    """CWD-only overrides (ACP adapter workspace tracking) must NOT trigger
+    container isolation — they should collapse to the shared 'default'
+    container so all surfaces (TUI, gateway, dashboard) share one sandbox.
+    Regression for #37361."""
+    terminal_tool.register_task_env_overrides(
+        "acp-session-abc", {"cwd": "/home/user/project"}
+    )
+    try:
+        assert (
+            terminal_tool._resolve_container_task_id("acp-session-abc")
+            == "default"
+        )
+    finally:
+        terminal_tool.clear_task_env_overrides("acp-session-abc")
+
+
+def test_cwd_plus_docker_image_keeps_own_id():
+    """When overrides include both cwd AND docker_image, isolation must
+    still be honoured (RL/benchmark pattern with explicit cwd)."""
+    terminal_tool.register_task_env_overrides(
+        "rl-with-cwd", {"docker_image": "myimg:latest", "cwd": "/workspace"}
+    )
+    try:
+        assert (
+            terminal_tool._resolve_container_task_id("rl-with-cwd")
+            == "rl-with-cwd"
+        )
+    finally:
+        terminal_tool.clear_task_env_overrides("rl-with-cwd")
+
+
+def test_env_type_override_keeps_own_id():
+    """env_type is an isolation key — must trigger per-task container."""
+    terminal_tool.register_task_env_overrides(
+        "bench-env", {"env_type": "sandbox", "cwd": "/work"}
+    )
+    try:
+        assert (
+            terminal_tool._resolve_container_task_id("bench-env")
+            == "bench-env"
+        )
+    finally:
+        terminal_tool.clear_task_env_overrides("bench-env")

tools/terminal_tool.py

@@ -1006,9 +1006,20 @@ def _resolve_container_task_id(task_id: Optional[str]) -> str:
     task_id, we honour it by returning the task_id unchanged -- those
     rollouts need their own isolated sandbox, which is the whole point of
     the override.
+
+    CWD-only overrides (registered by the ACP adapter for workspace
+    tracking) are *not* isolation signals — they should not cause each
+    session to spin up its own container.  Only overrides containing
+    backend-specific image keys or ``env_type`` trigger isolation.
     """
+    _ISOLATION_KEYS = frozenset({
+        "docker_image", "modal_image", "singularity_image",
+        "daytona_image", "env_type",
+    })
     if task_id and task_id in _task_env_overrides:
-        return task_id
+        overrides = _task_env_overrides[task_id]
+        if set(overrides.keys()) & _ISOLATION_KEYS:
+            return task_id
     return "default"