Fix CI app-suite deadlock: cooperative-pool-blocking thread-safety tests (#1339)

* Exclude perf baselines from parallel CI via --skip; sample hung tests

Every app-suite CI run since the perf baselines landed (#1335) has
timed out at the 15-minute job limit — main has been red for five
consecutive runs. The job logs show the PerformanceBaselineTests
fixtures dispatched into the parallel phase despite the
BITCHAT_SKIP_PERF_BASELINES env guard from #1336, followed by ~11
minutes of silence until the timeout kills swiftpm-testing. The suite
passes locally in seconds with identical flags, so the hang is
specific to the CI toolchain/runners — consistent with the known
XCTest-measure-under-parallel-workers hang the serial step was
created to avoid.

Two changes:
- Exclude the baselines from the parallel phase with --skip at the
  SPM level, which removes them from the worker processes entirely
  instead of relying on the env guard reaching setUpWithError. They
  still run (and gate) in the dedicated serial step.
- Wrap the parallel run in a 10-minute watchdog that samples any
  still-running test processes before killing them, so if anything
  else ever hangs, the run fails fast with thread stacks in the log
  instead of a silent 15-minute timeout.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Arm the test-hang watchdog only for the test execution phase

Codex review: swift test builds before running, so the watchdog timer
included dependency resolution and compilation — a cold-cache coverage
build on a slow runner could be killed before tests ever started.
Build the tests in their own step (bounded by the 15-minute job
timeout like any build) and run the watchdog around swift test
--skip-build, tightened to 5 minutes now that it times only test
execution.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* Hammer transport thread-safety tests from the dispatch pool, not the cooperative pool

The watchdog added in this PR captured the actual CI hang twice, with
identical stacks both times: NostrTransportTests' 100-task groups park
every Swift Concurrency cooperative thread in a blocking queue.sync
(the pool has one thread per core — 3 on CI runners, 10+ on dev
machines, which is why this never reproduced locally). Blocking the
entire cooperative pool violates the forward-progress contract, and
the runners' dispatch wedges under the resulting asyncAndWait flood —
taking concurrently running tests down with it (the panic-reset test
deadlocked in a serviceQueue barrier that never got scheduled).

Run the same 100 concurrent hammer iterations via
DispatchQueue.concurrentPerform from a single global-queue hop instead:
identical thread-safety coverage, executed on dispatch worker threads
where blocking is legal, zero cooperative threads parked.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: jack <jackjackbits@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

.github/workflows/swift-tests.yml

@@ -41,14 +41,50 @@ jobs:
             ${{ runner.os }}-${{ matrix.name }}-${{ hashFiles(format('{0}/**/Package.resolved', matrix.path)) }}
             ${{ runner.os }}-${{ matrix.name }}-
 
+      - name: Build tests
+        # Built separately so the hang watchdog below times only test
+        # execution: a cold-cache coverage build on a slow runner can
+        # legitimately take several minutes, and is already bounded by the
+        # 15-minute job timeout.
+        run: swift build --build-tests --enable-code-coverage --package-path ${{ matrix.path }}
+
       - name: Run Tests
         # Perf benchmarks are excluded here and run in their own serial step
         # below: measuring while parallel test processes contend for cores
         # produces noisy numbers, and the XCTest measure machinery has hung
-        # intermittently under parallel workers on loaded runners.
+        # intermittently under parallel workers on loaded runners. Excluded
+        # via --skip (not just the env guard): every app run since the
+        # baselines landed timed out at the 15-minute job limit with the
+        # baseline tests dispatched into the parallel phase.
+        #
+        # The watchdog samples any still-running test processes after 5
+        # minutes (the suite passes in seconds when healthy; the build is
+        # done by this step) and kills the run, so a hang fails fast with
+        # stacks in the log instead of a silent timeout.
         env:
           BITCHAT_SKIP_PERF_BASELINES: "1"
-        run: swift test --parallel --quiet --enable-code-coverage --package-path ${{ matrix.path }}
+        run: |
+          swift test --skip-build --parallel --quiet --enable-code-coverage \
+            --skip PerformanceBaselineTests \
+            --package-path ${{ matrix.path }} &
+          test_pid=$!
+          (
+            sleep 300
+            if kill -0 "$test_pid" 2>/dev/null; then
+              echo "::group::Tests still running after 5 minutes — sampling before kill"
+              for pid in $(pgrep -if 'swiftpm-testing|xctest|PackageTests' || true); do
+                echo "--- sample of pid $pid ---"
+                sample "$pid" 5 2>/dev/null || true
+              done
+              echo "::endgroup::"
+              pkill -KILL -P "$test_pid" 2>/dev/null || true
+              kill -KILL "$test_pid" 2>/dev/null || true
+            fi
+          ) &
+          watchdog_pid=$!
+          wait "$test_pid" && status=0 || status=$?
+          kill "$watchdog_pid" 2>/dev/null || true
+          exit "$status"
 
       # Benchmarks run serially on an otherwise idle runner for stable
       # numbers; BITCHAT_PERF_LOG captures the PERF[...] lines for the gate.