From e4051d725811cc47a384f908b3ca5717ff7e1f9f Mon Sep 17 00:00:00 2001
From: Speculator55005 <50082482+fas89@users.noreply.github.com>
Date: Fri, 30 Oct 2026 19:13:07 +0100
Subject: [PATCH] ci: a sysmon check, not a 30-minute cap, catches the coverage
 fallback

#770 cut the coverage job's timeout to 30 minutes so that a fallback to
the C tracer (~40 min) would fail instead of only slowing CI. GitHub
enforces that timeout server-side, and on 8d8c64b8 it cancelled a run
whose 30500 tests and coverage gates had passed at 21 minutes, after
GitHub stopped registering the job's step updates. 45 minutes leaves
room for that lag.

The fallback is caught by a step instead: coverage.py's --debug=core
logs the core it would use, and the step fails in a second unless it
is sysmon. Same COVERAGE_CORE and [tool.coverage.run] config as the run.
---
 .github/workflows/ci.yml | 32 ++++++++++++++++++++++++++------
 1 file changed, 26 insertions(+), 6 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 314eeffee..eed1bcca7 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -272,11 +272,13 @@ jobs:
   coverage-and-audit:
     name: Coverage & Audit (Python 3.14)
     runs-on: ubuntu-latest
-    # Under sysmon the run takes about as long as a plain test leg. 30
-    # bounds a true hang to minutes, not GitHub's 6-hour default, and is
-    # under the ~40 min a fallback to the C tracer takes, so a silent
-    # fallback fails the job instead of only slowing it.
-    timeout-minutes: 30
+    # Under sysmon the run takes about as long as a plain test leg, 12-22
+    # min. 45 bounds a true hang, not GitHub's 6-hour default, and leaves
+    # room for GitHub's own status lag: this timeout is enforced server-side,
+    # and on 2026-10-30 a 30-minute cap cancelled a run on main whose tests
+    # and gates had all passed. A fallback to the C tracer is caught by the
+    # "Coverage measures with sysmon" step, not by this timeout.
+    timeout-minutes: 45
     env:
       # Same glibc-arena cap as the test matrix (see comment there) —
       # this is the identical thread-heavy pytest run, plus coverage.
@@ -284,7 +286,8 @@ jobs:
       # Set, not left to the 3.14 default: a default sysmon that meets a
       # setting it cannot serve (a plugin, dynamic contexts) falls back to
       # the C tracer without a word; set explicitly, coverage.py 7.17
-      # still falls back but logs a `no-sysmon` CoverageWarning.
+      # still falls back but logs a `no-sysmon` CoverageWarning, and the
+      # "Coverage measures with sysmon" step fails the job on it.
       COVERAGE_CORE: sysmon
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
@@ -317,6 +320,23 @@ jobs:
           # distribution whose emitter differences are not what this tests.
           pip install "dbt-core<2" dbt-duckdb
 
+      # coverage.py picks its core when measurement starts, from this job's
+      # COVERAGE_CORE and the [tool.coverage.run] config that pytest-cov
+      # reads too, so a one-line script shows in a second what the C tracer
+      # would otherwise show as a ~40-minute run. `--debug=core` logs the
+      # choice: "Using core=sysmon" or "Using core=ctrace".
+      - name: Coverage measures with sysmon
+        run: |
+          echo "pass" > "$RUNNER_TEMP/noop.py"
+          COVERAGE_DEBUG=core COVERAGE_DEBUG_FILE="$RUNNER_TEMP/core.log" \
+            python -m coverage run --source="$RUNNER_TEMP" \
+            --data-file="$RUNNER_TEMP/.coverage.core" "$RUNNER_TEMP/noop.py"
+          cat "$RUNNER_TEMP/core.log"
+          if ! grep -q "Using core=sysmon" "$RUNNER_TEMP/core.log"; then
+            echo "::error::coverage.py would not measure with sys.monitoring, so the run below would take ~40 min (see #770)."
+            exit 1
+          fi
+
       # ── Tests + Coverage ────────────────────────────────────────
       - name: Run tests with coverage
         run: |