refactor(tools): consolidate task-override lookup into one helper

The raw-key-first-then-collapsed override lookup was hand-rolled in three
places with subtly different spellings: terminal_tool's command setup, and
both file_tools._registered_task_cwd_override and _get_file_ops. Since that
exact raw-vs-collapsed invariant is what the session-cwd fix depends on,
keeping three copies invites the drift that caused the original bug.

Add terminal_tool.resolve_task_overrides(task_id) as the single source and
route all three sites through it. Behaviour is unchanged (verified
byte-equivalent across raw/collapsed/isolation/None/subagent inputs).

tools/file_tools.py

@@ -123,15 +123,9 @@ def _registered_task_cwd_override(task_id: str = "default") -> str | None:
     read that raw override before falling back to the collapsed container key.
     """
     try:
-        from tools.terminal_tool import _resolve_container_task_id, _task_env_overrides
+        from tools.terminal_tool import resolve_task_overrides
 
-        raw_task_id = task_id or "default"
-        container_key = _resolve_container_task_id(raw_task_id)
-        overrides = (
-            _task_env_overrides.get(raw_task_id)
-            or _task_env_overrides.get(container_key)
-            or {}
-        )
+        overrides = resolve_task_overrides(task_id)
     except Exception:
         return None
 
@@ -693,15 +687,11 @@ def _get_file_ops(task_id: str = "default") -> ShellFileOperations:
                 terminal_env = None
 
         if terminal_env is None:
-            from tools.terminal_tool import _task_env_overrides
+            from tools.terminal_tool import resolve_task_overrides
 
             config = _get_env_config()
             env_type = config["env_type"]
-            overrides = (
-                _task_env_overrides.get(raw_task_id)
-                or _task_env_overrides.get(task_id)
-                or {}
-            )
+            overrides = resolve_task_overrides(raw_task_id)
 
             if env_type == "docker":
                 image = overrides.get("docker_image") or config["docker_image"]

tools/terminal_tool.py

@@ -1034,6 +1034,26 @@ def _resolve_container_task_id(task_id: Optional[str]) -> str:
     return "default"
 
 
+def resolve_task_overrides(task_id: Optional[str]) -> Dict[str, Any]:
+    """Return the env overrides for *task_id*, raw key first then collapsed.
+
+    ``register_task_env_overrides`` writes under the *raw* task/session id, but
+    a CWD-only override collapses (:func:`_resolve_container_task_id`) to the
+    shared ``"default"`` container so per-session surfaces (ACP/gateway/
+    dashboard) don't each spin up their own sandbox. Callers that need the
+    override (terminal command setup, file-tool cwd resolution) must therefore
+    read the raw id FIRST and only fall back to the collapsed container id, or
+    the originating session's override is silently dropped. This is the single
+    source of that lookup so the terminal and file layers can't drift apart.
+    """
+    raw = task_id or "default"
+    return (
+        _task_env_overrides.get(raw)
+        or _task_env_overrides.get(_resolve_container_task_id(raw))
+        or {}
+    )
+
+
 # Configuration from environment variables
 
 def _parse_env_var(name: str, default: str, converter: Any = int, type_label: str = "integer"):
@@ -1885,20 +1905,12 @@ def terminal_tool(
         effective_task_id = _resolve_container_task_id(task_id)
 
         # Check per-task overrides (set by environments like TerminalBench2Env)
-        # before falling back to global env var config.
-        #
-        # Overrides are keyed by the *raw* task_id (that's the key
-        # ``register_task_env_overrides`` writes under), NOT by the collapsed
-        # container id. A CWD-only override collapses ``effective_task_id`` to
-        # ``"default"`` for container sharing, but its cwd must still be read
-        # back here under the originating task_id, or the override is silently
-        # dropped. Fall back to the collapsed id so isolation-keyed RL/benchmark
-        # overrides (registered under an id that equals their container id) keep
-        # resolving as before.
-        overrides = (
-            (_task_env_overrides.get(task_id) if task_id else None)
-            or _task_env_overrides.get(effective_task_id, {})
-        )
+        # before falling back to global env var config. ``resolve_task_overrides``
+        # reads the raw task id first then the collapsed container id, so a
+        # CWD-only override (which collapses ``effective_task_id`` to
+        # ``"default"``) is still found under its originating session id while
+        # isolation-keyed RL/benchmark overrides keep resolving as before.
+        overrides = resolve_task_overrides(task_id)
         
         # Select image based on env type, with per-task override support
         if env_type == "docker":