feat(xce-test-cli-ux): add per-connection lock to interruptible-call adapter

A registry of per-connection locks, acquired (interruptibly) before
spawning a worker and released by whichever side finishes last, so an
abandoned call's worker is never running concurrently with a new call
on the same connection. Uses a POSIX semaphore (sem_t), not a mutex:
review round 1 found the initial pthread_mutex_t implementation relied
on behavior POSIX classifies as undefined for a non-owning-thread
unlock (not just error-checking mutex types) -- this design's worker
thread legitimately releases a lock the caller thread acquired, which
sem_t supports with no ownership concept at all. bug-1791. Design.md
synced to reflect the semaphore choice. 1285/1285 controller suite
passing.

Task 1.5 of .kiro/specs/xce-test-cli-ux/tasks.md.
Requirements: 1.1, 1.5

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019jaMf9QEwpugH2W9KAuc7f

.wolf/buglog.json

@@ -21465,6 +21465,31 @@
       ],
       "occurrences": 1,
       "last_seen": "2026-09-08T00:00:00Z"
+    },
+    {
+      "id": "bug-1791",
+      "timestamp": "2026-09-09T08:50:58.000Z",
+      "error_message": "controller_unit_test: interruptcall.c:142: xcetest_worker_main: Assertion \\`unlock_rc == 0' failed (pthread_mutex_unlock returned EPERM)",
+      "file": "src/controller/testsuite/interruptcall.c",
+      "root_cause": "xce-test-cli-ux task 1.5's per-connection lock registry initialized each connection's pthread_mutex_t with PTHREAD_MUTEX_ERRORCHECK, intended to catch double-unlock/never-unlocked regressions. But this design's own ownership-handoff protocol (design.md/research.md's 'per-connection lock' decision) REQUIRES a legitimate cross-thread release on the abandonment path: the calling (REPL) thread acquires the lock via pthread_mutex_trylock(), but on abandonment the still-running detached WORKER thread is the one that must release it later, once fn() finishes -- ownership of 'release the lock' passes to the worker at the same moment ownership of the heap call block does. PTHREAD_MUTEX_ERRORCHECK (and _RECURSIVE) mutexes track a single owning thread and reject pthread_mutex_unlock() from any other thread with EPERM, which fired immediately on the very first same-key-serialization test.",
+      "fix": "Switched the per-connection lock registry (xcetest_conn_lock_for() in interruptcall.c) to initialize each mutex with the DEFAULT type (pthread_mutex_init(&node->mutex, NULL)) instead of PTHREAD_MUTEX_ERRORCHECK. glibc default (PTHREAD_MUTEX_NORMAL-equivalent) mutexes do not track a per-thread owner, so a worker thread may validly unlock a mutex the REPL thread locked. Kept the assert(pthread_mutex_unlock(...) == 0) safety-net checks at every release site (computed outside the assert() expression itself, so the unlock call is never skipped under NDEBUG) as a lower-cost guard against genuine corruption, without relying on error-checking-mutex semantics that conflict with the intentional cross-thread handoff. SUPERSEDED 2026-09-09 (task 1.5 remediation round 1, independent review): an external reviewer correctly pointed out that POSIX classifies non-owning-thread pthread_mutex_unlock() as undefined behavior for PTHREAD_MUTEX_NORMAL/DEFAULT too, not just ERRORCHECK/_RECURSIVE -- NORMAL is merely *permitted* not to detect the violation, not declared well-defined for it. The DEFAULT-mutex fix above was therefore empirically safe on XCE's glibc/NPTL-exclusive Nix build but relied on non-portable, POSIX-UB behavior, under-documented as such. Replaced the pthread_mutex_t per-connection lock with a POSIX semaphore (sem_t, binary, sem_init(&sem, 0, 1)) throughout: sem_trywait() in place of pthread_mutex_trylock() (EAGAIN in place of EBUSY) in the interruptible poll loop, and sem_post() in place of pthread_mutex_unlock() at every release site (both the caller-normal-completion path and the worker-abandoned-cleanup cross-thread path). sem_t has no ownership concept, so this cross-thread release is now fully POSIX-defined with no UB reliance at all, at the same code complexity. All 1285 controller_unit_test tests (including the 3 task-1.5-specific tests) continued to pass unchanged after the migration.",
+      "tags": [
+        "pthread",
+        "mutex",
+        "EPERM",
+        "cross-thread-unlock",
+        "ownership-handoff",
+        "xce-test-cli-ux",
+        "task-1.5",
+        "interruptcall.c",
+        "design-review-caught-by-test",
+        "posix-ub",
+        "sem_t",
+        "semaphore-migration"
+      ],
+      "related_bugs": [],
+      "occurrences": 1,
+      "last_seen": "2026-09-09T08:50:58.000Z"
     }
   ]
 }