Claude-perms: ensure /commit-msg files can be written!

Two-part stopgap for the still-hanging
`test_nested_multierrors[subint_forkserver]`:

1. Skip-mark the test via
   `@pytest.mark.skipon_spawn_backend('subint_forkserver',
   reason=...)` so it stops blocking the test
   matrix while the remaining bug is being chased.
   The reason string cross-refs the conc-anal doc
   for full context.

2. Update the conc-anal doc
   (`subint_forkserver_test_cancellation_leak_issue.md`) with the
   empirical state after the three nested- cancel fix commits
   (`0cd0b633` FD scrub + `fe540d02` pidfd wait + `57935804` parent-chan
   shield break) landed, narrowing the remaining hang from "everything
   broken" to "peer-channel loops don't exit on `service_tn` cancel".

Deats from the DIAGDEBUG instrumentation pass,
- 80 `process_messages` ENTERs, 75 EXITs → 5 stuck
- ALL 40 `shield=True` ENTERs matched EXIT — the
  `_parent_chan_cs.cancel()` wiring from `57935804`
  works as intended for shielded loops.
- the 5 stuck loops are all `shield=False` peer-
  channel handlers in `handle_stream_from_peer`
  (inbound connections handled by
  `stream_handler_tn`, which IS `service_tn` in the
  current config).
- after `_parent_chan_cs.cancel()` fires, NEW
  shielded loops appear on the session reg_addr
  port — probably discovery-layer reconnection;
  doesn't block teardown but indicates the cascade
  has more moving parts than expected.

The remaining unknown: why don't the 5 peer-channel loops exit when
`service_tn.cancel_scope.cancel()` fires? They're not shielded, they're
inside the service_tn scope, a standard cancel should propagate through.
Some fork-config-specific divergence keeps them alive. Doc lists three
follow-up experiments (stackscope dump, side-by-side `trio_proc`
comparison, audit of the `tractor/ipc/_server.py:448` `except
trio.Cancelled:` path).

(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code

.claude/settings.local.json

@@ -1,8 +1,16 @@
 {
   "permissions": {
     "allow": [
-      "Bash(date *)",
       "Bash(cp .claude/*)",
+      "Read(.claude/**)",
+      "Read(.claude/skills/run-tests/**)",
+      "Write(.claude/**/*commit_msg*)",
+      "Write(.claude/git_commit_msg_LATEST.md)",
+      "Skill(run-tests)",
+      "Skill(close-wkt)",
+      "Skill(open-wkt)",
+      "Skill(prompt-io)",
+      "Bash(date *)",
       "Bash(git diff *)",
       "Bash(git log *)",
       "Bash(git status)",
@@ -23,14 +31,12 @@
       "Bash(UV_PROJECT_ENVIRONMENT=py* uv sync:*)",
       "Bash(UV_PROJECT_ENVIRONMENT=py* uv run:*)",
       "Bash(echo EXIT:$?:*)",
-      "Write(.claude/*commit_msg*)",
+      "Bash(echo \"EXIT=$?\")",
-      "Write(.claude/git_commit_msg_LATEST.md)",
+      "Read(//tmp/**)"
-      "Skill(run-tests)",
-      "Skill(close-wkt)",
-      "Skill(open-wkt)",
-      "Skill(prompt-io)"
     ],
     "deny": [],
     "ask": []
-  }
+  },
+  "prefersReducedMotion": false,
+  "outputStyle": "default"
 }

ai/conc-anal/subint_forkserver_test_cancellation_leak_issue.md

@@ -306,13 +306,103 @@ root's `open_nursery` receives the
 `BaseExceptionGroup` containing the `AssertionError`
 from the errorer and unwinds cleanly.
 
+## Update — 2026-04-23: partial fix landed, deeper layer surfaced
+
+Three improvements landed as separate commits in the
+`subint_forkserver_backend` branch (see `git log`):
+
+1. **`_close_inherited_fds()` in fork-child prelude**
+   (`tractor/spawn/_subint_forkserver.py`). POSIX
+   close-fds-equivalent enumeration via
+   `/proc/self/fd` (or `RLIMIT_NOFILE` fallback), keep
+   only stdio. This is fix-direction (1) from the list
+   above — went with the blunt form rather than the
+   targeted enum-via-`actor.ipc_server` form, turns
+   out the aggressive close is safe because every
+   inheritable resource the fresh child needs
+   (IPC-channel socket, etc.) is opened AFTER the
+   fork anyway.
+2. **`_ForkedProc.wait()` via `os.pidfd_open()` +
+   `trio.lowlevel.wait_readable()`** — matches the
+   `trio.Process.wait` / `mp.Process.sentinel` pattern
+   used by `trio_proc` and `proc_waiter`. Gives us
+   fully trio-cancellable child-wait (prior impl
+   blocked a cache thread on a sync `os.waitpid` that
+   was NOT trio-cancellable due to
+   `abandon_on_cancel=False`).
+3. **`_parent_chan_cs` wiring** in
+   `tractor/runtime/_runtime.py`: capture the shielded
+   `loop_cs` for the parent-channel `process_messages`
+   task in `async_main`; explicitly cancel it in
+   `Actor.cancel()` teardown. This breaks the shield
+   during teardown so the parent-chan loop exits when
+   cancel is issued, instead of parking on a parent-
+   socket EOF that might never arrive under fork
+   semantics.
+
+**Concrete wins from (1):** the sibling
+`subint_forkserver_orphan_sigint_hang_issue.md` class
+is **now fixed** — `test_orphaned_subactor_sigint_cleanup_DRAFT`
+went from strict-xfail to pass. The xfail mark was
+removed; the test remains as a regression guard.
+
+**test_nested_multierrors STILL hangs** though.
+
+### Updated diagnosis (narrowed)
+
+DIAGDEBUG instrumentation of `process_messages` ENTER/
+EXIT pairs + `_parent_chan_cs.cancel()` call sites
+showed (captured during a 20s-timeout repro):
+
+- 80 `process_messages` ENTERs, 75 EXITs → 5 stuck.
+- **All 40 `shield=True` ENTERs matched EXIT** — every
+  shielded parent-chan loop exits cleanly. The
+  `_parent_chan_cs` wiring works as intended.
+- **The 5 stuck loops are all `shield=False`** — peer-
+  channel handlers (inbound connections handled by
+  `handle_stream_from_peer` in stream_handler_tn).
+- After our `_parent_chan_cs.cancel()` fires, NEW
+  shielded process_messages loops start (on the
+  session reg_addr port — probably discovery-layer
+  reconnection attempts). These don't block teardown
+  (they all exit) but indicate the cancel cascade has
+  more moving parts than expected.
+
+### Remaining unknown
+
+Why don't the 5 peer-channel loops exit when
+`service_tn.cancel_scope.cancel()` fires? They're in
+`stream_handler_tn` which IS `service_tn` in the
+current configuration (`open_ipc_server(parent_tn=
+service_tn, stream_handler_tn=service_tn)`). A
+standard nursery-scope-cancel should propagate through
+them — no shield, no special handler. Something
+specific to the fork-spawned configuration keeps them
+alive.
+
+Candidate follow-up experiments:
+
+- Dump the trio task tree at the hang point (via
+  `stackscope` or direct trio introspection) to see
+  what each stuck loop is awaiting. `chan.__anext__`
+  on a socket recv? An inner lock? A shielded sub-task?
+- Compare peer-channel handler lifecycle under
+  `trio_proc` vs `subint_forkserver` with equivalent
+  logging to spot the divergence.
+- Investigate whether the peer handler is caught in
+  the `except trio.Cancelled:` path at
+  `tractor/ipc/_server.py:448` that re-raises — but
+  re-raise means it should still exit. Unless
+  something higher up swallows it.
+
 ## Stopgap (landed)
 
-Until the fix lands, `test_nested_multierrors` +
+`test_nested_multierrors` skip-marked under
-related multi-level-spawn tests can be skip-marked
+`subint_forkserver` via
-under `subint_forkserver` via
 `@pytest.mark.skipon_spawn_backend('subint_forkserver',
-reason='...')`. Cross-ref this doc.
+reason='...')`, cross-referenced to this doc. Mark
+should be dropped once the peer-channel-loop exit
+issue is fixed.
 
 ## References
 

tests/spawn/test_subint_forkserver.py

@@ -446,22 +446,15 @@ def _process_alive(pid: int) -> bool:
         return False
 
 
-@pytest.mark.xfail(
+# NOTE: was previously `@pytest.mark.xfail(strict=True, ...)`
-    strict=True,
+# for the orphan-SIGINT hang documented in
-    reason=(
+# `ai/conc-anal/subint_forkserver_orphan_sigint_hang_issue.md`
-        'subint_forkserver orphan-child SIGINT hang: trio\'s '
+# — now passes after the fork-child FD-hygiene fix in
-        'event loop stays wedged in `epoll_wait` despite the '
+# `tractor.spawn._subint_forkserver._close_inherited_fds()`:
-        'SIGINT handler being correctly installed and the '
+# closing all inherited FDs (including the parent's IPC
-        'signal being delivered at the kernel level. NOT a '
+# listener + trio-epoll + wakeup-pipe FDs) lets the child's
-        '"handler missing on non-main thread" issue — post-'
+# trio event loop respond cleanly to external SIGINT.
-        'fork the worker IS `threading.main_thread()` and '
+# Leaving the test in place as a regression guard.
-        'trio\'s `KIManager` handler is confirmed installed. '
-        'Full analysis + ruled-out hypotheses + fix directions '
-        'in `ai/conc-anal/'
-        'subint_forkserver_orphan_sigint_hang_issue.md`. '
-        'Flip this mark (or drop it) once the gap is closed.'
-    ),
-)
 @pytest.mark.timeout(
     30,
     method='thread',

tests/test_cancellation.py

@@ -452,6 +452,19 @@ async def spawn_and_error(
             await nursery.run_in_actor(*args, **kwargs)
 
 
+@pytest.mark.skipon_spawn_backend(
+    'subint_forkserver',
+    reason=(
+        'Multi-level fork-spawn cancel cascade hang — '
+        'peer-channel `process_messages` loops do not '
+        'exit on `service_tn.cancel_scope.cancel()`. '
+        'See `ai/conc-anal/'
+        'subint_forkserver_test_cancellation_leak_issue.md` '
+        'for the full diagnosis + candidate fix directions. '
+        'Drop this mark once the peer-chan-loop exit issue '
+        'is closed.'
+    ),
+)
 @pytest.mark.timeout(
     10,
     method='thread',

tractor/runtime/_runtime.py

@@ -1216,6 +1216,23 @@ class Actor:
                 ipc_server.cancel()
                 await ipc_server.wait_for_shutdown()
 
+            # Break the shield on the parent-channel
+            # `process_messages` loop (started with `shield=True`
+            # in `async_main` above). Required to avoid a
+            # deadlock during teardown of fork-spawned subactors:
+            # without this cancel, the loop parks waiting for
+            # EOF on the parent channel, but the parent is
+            # blocked on `os.waitpid()` for THIS actor's exit
+            # — mutual wait. For exec-spawn backends the EOF
+            # arrives naturally when the parent closes its
+            # handler-task socket during its own teardown, but
+            # in fork backends the shared-process-image makes
+            # that delivery racy / not guaranteed. Explicit
+            # cancel here gives us deterministic unwinding
+            # regardless of backend.
+            if self._parent_chan_cs is not None:
+                self._parent_chan_cs.cancel()
+
             # cancel all rpc tasks permanently
             if self._service_tn:
                 self._service_tn.cancel_scope.cancel()
@@ -1736,7 +1753,16 @@ async def async_main(
                 # start processing parent requests until our channel
                 # server is 100% up and running.
                 if actor._parent_chan:
-                    await root_tn.start(
+                    # Capture the shielded `loop_cs` for the
+                    # parent-channel `process_messages` task so
+                    # `Actor.cancel()` has a handle to break the
+                    # shield during teardown — without this, the
+                    # shielded loop would park on the parent chan
+                    # indefinitely waiting for EOF that only arrives
+                    # after the PARENT tears down, which under
+                    # fork-based backends (e.g. `subint_forkserver`)
+                    # it waits on THIS actor's exit — deadlock.
+                    actor._parent_chan_cs = await root_tn.start(
                         partial(
                             _rpc.process_messages,
                             chan=actor._parent_chan,

tractor/spawn/_subint_forkserver.py

@@ -526,6 +526,18 @@ class _ForkedProc:
         self.stdin = None
         self.stdout = None
         self.stderr = None
+        # pidfd (Linux 5.3+, Python 3.9+) — a file descriptor
+        # referencing this child process which becomes readable
+        # once the child exits. Enables a fully trio-cancellable
+        # wait via `trio.lowlevel.wait_readable()` — same
+        # pattern `trio.Process.wait()` uses under the hood, and
+        # the same pattern `multiprocessing.Process.sentinel`
+        # uses for `tractor.spawn._spawn.proc_waiter()`. Without
+        # this, waiting via `trio.to_thread.run_sync(os.waitpid,
+        # ...)` blocks a cache thread on a sync syscall that is
+        # NOT trio-cancellable, which prevents outer cancel
+        # scopes from unwedging a stuck-child cancel cascade.
+        self._pidfd: int = os.pidfd_open(pid)
 
     def poll(self) -> int | None:
         '''
@@ -555,22 +567,40 @@ class _ForkedProc:
 
     async def wait(self) -> int:
         '''
-        Async blocking wait for the child's exit, off-loaded
+        Async, fully-trio-cancellable wait for the child's
-        to a trio cache thread so we don't block the event
+        exit. Uses `trio.lowlevel.wait_readable()` on the
-        loop on `waitpid()`. Safe to call multiple times;
+        `pidfd` sentinel — same pattern as `trio.Process.wait`
-        subsequent calls return the cached rc without
+        and `tractor.spawn._spawn.proc_waiter` (mp backend).
-        re-issuing the syscall.
+
+        Safe to call multiple times; subsequent calls return
+        the cached rc without re-issuing the syscall.
 
         '''
         if self._returncode is not None:
             return self._returncode
-        _, status = await trio.to_thread.run_sync(
+        # Park until the pidfd becomes readable — the OS
-            os.waitpid,
+        # signals this exactly once on child exit. Cancellable
-            self.pid,
+        # via any outer trio cancel scope (this was the key
-            0,
+        # fix vs. the prior `to_thread.run_sync(os.waitpid,
-            abandon_on_cancel=False,
+        # abandon_on_cancel=False)` which blocked a thread on
-        )
+        # a sync syscall and swallowed cancels).
+        await trio.lowlevel.wait_readable(self._pidfd)
+        # pidfd signaled → reap non-blocking to collect the
+        # exit status. `WNOHANG` here is correct: by the time
+        # the pidfd is readable, `waitpid()` won't block.
+        try:
+            _, status = os.waitpid(self.pid, os.WNOHANG)
+        except ChildProcessError:
+            # already reaped by something else
+            status = 0
         self._returncode = self._parse_status(status)
+        # pidfd is one-shot; close it so we don't leak fds
+        # across many spawns.
+        try:
+            os.close(self._pidfd)
+        except OSError:
+            pass
+        self._pidfd = -1
         return self._returncode
 
     def kill(self) -> None:
@@ -584,6 +614,16 @@ class _ForkedProc:
         except ProcessLookupError:
             pass
 
+    def __del__(self) -> None:
+        # belt-and-braces: close the pidfd if `wait()` wasn't
+        # called (e.g. unexpected teardown path).
+        fd: int = getattr(self, '_pidfd', -1)
+        if fd >= 0:
+            try:
+                os.close(fd)
+            except OSError:
+                pass
+
     def _parse_status(self, status: int) -> int:
         if os.WIFEXITED(status):
             return os.WEXITSTATUS(status)