Address Copilot review fixes on `maybe_open_context()`

Deats,
- drop unused `import tractor` (F401)
- fix `_Cache.locks` annotation to `trio.StrictFIFOLock`
- fix typos: "mabye-value", "Acquir lock"
- add `resources.pop()` cleanup in the caller if
  `service_tn.start()` fails — prevents a
  permanent `_Cache.resources` leak on
  `__aenter__` failure (note: Copilot's suggested
  outer `try/finally` in `run_ctx` would
  re-introduce the atomicity gap)
- add `user_registered` flag so `users -= 1` only
  runs when the task actually incremented
- move lock pop into the `users <= 0` teardown
  block so the last exiting user always cleans up,
  regardless of who created the lock; drop
  now-dead `lock_registered` var

Also,
- swap `fid` for `ctx_key` in debug log msgs
- remove stale commented-out `# fid` refs

Review: PR #436 (copilot-pull-request-reviewer)
https://github.com/goodboy/tractor/pull/436

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

tractor/trionics/_mngrs.py

@@ -40,7 +40,6 @@ from typing import (
 import trio
 from tractor.runtime._state import current_actor
 from tractor.log import get_logger
-import tractor
 # from ._beg import collapse_eg
 # from ._taskc import (
 #     maybe_raise_from_masking_exc,
@@ -206,7 +205,7 @@ class _Cache:
 
     '''
     service_tn: trio.Nursery|None = None
-    locks: dict[Hashable, trio.Lock] = {}
+    locks: dict[Hashable, trio.StrictFIFOLock] = {}
     users: defaultdict[
         tuple|Hashable,
         int,
@@ -240,7 +239,7 @@ class _Cache:
 
 class _UnresolvedCtx:
     '''
-    Placeholder for the mabye-value delivered from some `acm_func`,
+    Placeholder for the maybe-value delivered from some `acm_func`,
     once (first) entered by a `maybe_open_context()` task.
 
     Enables internal teardown logic conditioned on whether the
@@ -284,7 +283,7 @@ async def maybe_open_context(
     # yielded output
     # sentinel = object()
     yielded: Any = _UnresolvedCtx
-    lock_registered: bool = False
+    user_registered: bool = False
 
     # Lock resource acquisition around task racing  / ``trio``'s
     # scheduler protocol.
@@ -293,17 +292,13 @@ async def maybe_open_context(
     # wrapped factory may want to call into another.
     task: trio.Task = trio.lowlevel.current_task()
     lock: trio.StrictFIFOLock|None = _Cache.locks.get(
-        # fid
         ctx_key
     )
     if not lock:
         lock = _Cache.locks[
             ctx_key
-            # fid
         ] = trio.StrictFIFOLock()
-        # lock = _Cache.locks[fid] = trio.Lock()
         header: str = 'Allocated NEW lock for @acm_func,\n'
-        lock_registered: bool = True
     else:
         await trio.lowlevel.checkpoint()
         header: str = 'Reusing OLD lock for @acm_func,\n'
@@ -312,14 +307,14 @@ async def maybe_open_context(
         f'{header}'
         f'Acquiring..\n'
         f'task={task!r}\n'
-        f'fid={fid!r}\n'
+        f'ctx_key={ctx_key!r}\n'
         f'acm_func={acm_func}\n'
     )
     await lock.acquire()
     log.debug(
-        f'Acquir lock..\n'
+        f'Acquired lock..\n'
         f'task={task!r}\n'
-        f'fid={fid!r}\n'
+        f'ctx_key={ctx_key!r}\n'
         f'acm_func={acm_func}\n'
     )
 
@@ -385,12 +380,21 @@ async def maybe_open_context(
                 )
 
             resources[ctx_key] = (service_tn, trio.Event())
+            try:
                 yielded: Any = await service_tn.start(
                     _Cache.run_ctx,
                     mngr,
                     ctx_key,
                 )
+            except BaseException:
+                # If `run_ctx` (wrapping the acm's `__aenter__`)
+                # fails or is cancelled, clean up the `resources`
+                # entry we just set — OW it leaks permanently.
+                # |_ https://github.com/goodboy/tractor/pull/436#discussion_r3047201323
+                resources.pop(ctx_key, None)
+                raise
             _Cache.users[ctx_key] += 1
+            user_registered = True
         finally:
             # XXX, since this runs from an `except` it's a checkpoint
             # which can be `trio.Cancelled`-masked.
@@ -427,6 +431,7 @@ async def maybe_open_context(
     else:
         # XXX, cached-entry-path
         _Cache.users[ctx_key] += 1
+        user_registered = True
         log.debug(
             f'Re-using cached resource for user {_Cache.users}\n\n'
             f'{ctx_key!r} -> {type(yielded)}\n'
@@ -451,13 +456,14 @@ async def maybe_open_context(
                 f'{stats}\n'
                 f'\n'
                 f'task={task!r}\n'
-                f'fid={fid!r}\n'
+                f'ctx_key={ctx_key!r}\n'
                 f'acm_func={acm_func}\n'
 
             )
             # XXX, trace it.
             # await tractor.pause(shield=True)
 
+        if user_registered:
             _Cache.users[ctx_key] -= 1
 
         if yielded is not _UnresolvedCtx:
@@ -477,7 +483,6 @@ async def maybe_open_context(
                     _, no_more_users = entry
                     no_more_users.set()
 
-                if lock_registered:
                 maybe_lock = _Cache.locks.pop(
                     ctx_key,
                     None,