ci(browser): a hung browser step fails with its running tests named and its traces kept (#425) (#429)

* ci(browser): stop a hung browser run before the job limit and name it

A browser job killed at its 20-minute limit keeps no log and skips its
upload steps (merge-queue run 40723857746, firefox shard 2/2), so nothing
showed which test hung.

- Each browser test step gets timeout-minutes 18, below the job's 20, so
  the step fails and the always() uploads still run.
- Under CI, Playwright's globalTimeout stops the run first:
  PM_TEST_GLOBAL_TIMEOUT_MINUTES 17 for page workflows, 15 for coverage
  workflows, a fixed 3 for the viewer suite. Locally there is no limit
  unless the variable is set. Each test keeps the 30 s default.
- running-tests-reporter.mjs prints the tests still running when the run
  ends; Playwright's own reporters cannot, since those tests never end.
- A blob report goes to tools/vendor/test-results/blob/, inside the
  uploaded traces path.
- ci-workflow.test.mjs pins globalTimeout < step limit < job limit and the
  always() uploads; no existing limit is raised.

Closes #425

* ci(browser): rely on the step limit, report the running tests on SIGTERM

Maintainer ruling on #425: no Playwright globalTimeout. The 18-minute
step limit under the unchanged 20-minute job limit stays, as do the
always() uploads and the CI blob report.

- Drop globalTimeout and PM_TEST_GLOBAL_TIMEOUT_MINUTES with its helper
  and tests.
- A step that reaches its limit gets SIGTERM, which ended Playwright with
  no report and no blob. The running-tests reporter now catches the first
  SIGTERM, prints the tests still running and sends Playwright its own
  SIGINT, so the run ends interrupted and the blob report is written. A
  second SIGTERM kills as usual.
- Test paths are relative to the suite's rootDir instead of the cwd, so
  `npm run --prefix` no longer prints ../../ prefixes.
- The workflow comment and TESTING.md say the guarantee assumes an npm
  cache hit and that coverage shard 1 is tight in its 18-minute step.

* ci(browser): forward SIGTERM and SIGINT from frontend-coverage.mjs to its child

In the coverage job npm signals only frontend-coverage.mjs. It blocked in
spawnSync with no listener, so Playwright never saw a step timeout. It now
runs each step's child with async spawn, in its own process group, and
forwards SIGTERM and SIGINT to the running child. Step order, exit codes
and the "Command failed (N)" message are unchanged.

Locally, in the pinned image, `timeout -s TERM` on test:coverage printed
the still-running tests and wrote both blob reports. TESTING.md records
that a SIGTERM to npm alone stops at npm's `sh -c`, and that delivery
through `docker exec` in CI is not yet observed.

Refs #425

* ci(browser): load the running-tests reporter by absolute path

A config imported from another directory (the workflow-artifacts test copies
it to a temp root) resolved './running-tests-reporter.mjs' against that root
under CI and failed to load it. Resolve it from this module instead.

.github/workflows/viewerjs-check.yml

@@ -27,6 +27,15 @@ concurrency:
 # coverage shards 7m34s/6m04s/5m22s (tests 6m38s/4m53s/4m04s), merge 54s, firefox 7m57s/5m21s (tests
 # 7m08s/4m34s), webkit 8m16s/5m03s (tests 7m26s/3m58s); a cache miss adds up to 5m to npm ci, which
 # the 20-minute limits absorb.
+# Hangs (#425): a job killed at its limit keeps no log and skips its upload steps, so each browser
+# test step has its own timeout-minutes (18) below the job's 20. At the step limit, SIGTERM makes
+# tools/vendor/running-tests-reporter.mjs print the tests still running and hand over to Playwright's
+# interrupt, which writes the blob report; the always() uploads then run.
+# Measured on main (runs 40725289094, 40719375442, 40700439399): setup before the test step <= 52s,
+# uploads <= 35s; test steps up to 14m42s (webkit shard 1/2) and 13m05s for coverage (shard 1/3:
+# 12m53s, node units and the viewer suite before 11.8m of workflows), so coverage is the tight one
+# in its 18 minutes. This holds only when the npm cache hits: a cold cache adds up to 5m to npm ci,
+# and then the job limit can still end the job before the step limit does.
 jobs:
   frontend-coverage:
     name: frontend coverage (shard ${{ matrix.shard }}/3)
@@ -79,6 +88,7 @@ jobs:
       - if: matrix.shard == 3
         run: npm run --prefix tools/vendor test
       - name: Page workflows with coverage, shard ${{ matrix.shard }}/3
+        timeout-minutes: 18
         run: npm run --prefix tools/vendor test:coverage:shard -- ${{ matrix.shard }}/3
       - name: Upload raw coverage
         uses: actions/upload-artifact@v7
@@ -87,6 +97,7 @@ jobs:
           path: coverage/js/raw/
           if-no-files-found: error
           retention-days: 3
+      # Traces and the blob report (test-results/blob/) of a failed, timed-out or cancelled step.
       - name: Upload Chromium and touch traces
         if: always()
         uses: actions/upload-artifact@v7
@@ -211,7 +222,9 @@ jobs:
           key: npm-${{ runner.os }}-playwright-v1.64.1-${{ hashFiles('tools/vendor/package-lock.json') }}
       - run: npm ci --prefix tools/vendor --ignore-scripts
       - name: Page workflows in ${{ matrix.browser }}, shard ${{ matrix.shard }}/2
+        timeout-minutes: 18
         run: npm run --prefix tools/vendor test:workflows -- --project ${{ matrix.browser }} --shard ${{ matrix.shard }}/2
+      # Traces and the blob report (test-results/blob/) of a failed, timed-out or cancelled step.
       - name: Upload browser traces
         if: always()
         uses: actions/upload-artifact@v7