fix(browser): server shutdown and its tests on Windows, Python < 3.13 and CI

Three CI failures on ed809f7: - Windows: server.py exited 1 on stdin EOF because create_app works with the temp root as its cwd, and Windows cannot remove a process's cwd. main() now restores the original cwd before the root is removed. - Python 3.10 to 3.12: the lifetime test's cleanup called communicate() after closing stdin, which flushes the closed pipe (ValueError); 3.13 tolerates it. It now waits and closes the pipes itself, and the exit assertion shows the server's stderr. Under 3.12: errors=2 before, OK after. - Tooling (CI container): the SIGKILLed-worker tests treated an exited server as alive, because the container's PID 1 does not reap orphans and kill(pid, 0) succeeds on a zombie. Reproduced locally with docker without --init (2 failed); a zombie now counts as exited (2 passed).
docs(testing): server lifetime, stderr attachments and the final measured CI times
2026-10-21 22:57:03 -07:00 · 2026-10-21 22:37:49 -07:00 · 2026-10-21 22:37:48 -07:00 · 2026-10-21 21:55:21 -07:00 · 2026-10-21 21:22:52 -07:00 · 2026-10-21 20:03:13 -07:00
41 changed files with 1389 additions and 110 deletions
@@ -16,9 +16,19 @@ concurrency:
  group: ${{ github.workflow }}-${{ github.event_name == 'pull_request' && github.ref || github.run_id }}
  cancel-in-progress: ${{ github.event_name == 'pull_request' }}

+# Timeouts are the measured job time plus at least 50%, and never under 20 minutes for a browser job,
+# because runner speed varies. Before sharding (main 2cecfcf, one worker): frontend coverage 32m10s,
+# page workflows firefox 18m59s, webkit 19m26s. First sharded run (PR #274 run 39712909047, 3 workers,
+# no npm cache, where npm ci stalled for 5m in six of eight jobs): coverage shards 11m19s/10m47s/10m49s
+# (tests 5m20s/4m42s/4m46s), merge 5m52s (report and check 4s), firefox shards 7m53s/9m27s (tests
+# 4m41s/3m29s), webkit shards 12m25s+ (cancelled at the old 12-minute limit after its 267 tests passed in
+# 6m29s) and 4m53s (tests 3m08s). With the npm cache hit (run 39725176320 at cbc8a61, npm ci 0-2s):
+# 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.
 jobs:
  frontend-coverage:
-    name: frontend coverage (chromium and touch)
+    name: frontend coverage (shard ${{ matrix.shard }}/3)
    runs-on: ubuntu-latest
    # Layout comparisons depend on the fonts each browser falls back to, so browser jobs run in the
    # same pinned Playwright image as local runs (tag = @playwright/test in tools/vendor/package-lock.json;
@@ -26,12 +36,15 @@ jobs:
    container:
      image: mcr.microsoft.com/playwright:v1.64.1-noble
      options: --user 1001
-    # This job runs every page workflow twice (chromium, then touch) on one worker with V8 coverage on, so it
-    # takes about twice a single-browser job. Measured 2026-10-20: whole job 18m26s-24m57s (main 5ded3cf
-    # 22m15s; PR head 6359999 was cancelled at the old 25-minute limit while still passing), coverage step
-    # alone 20m55s-22m17s+, against ~12-15 minutes for the firefox/webkit jobs. 40 minutes leaves headroom
-    # for suite growth while still stopping a hung run; re-measure if a run passes 30 minutes.
-    timeout-minutes: 40
+    timeout-minutes: 20
+    # Public-repo ubuntu-latest runners have 4 vCPUs: three Playwright workers, each with its own test
+    # server, leave one CPU for the servers and the runner.
+    env:
+      PM_TEST_WORKERS: 3
+    strategy:
+      fail-fast: false
+      matrix:
+        shard: [1, 2, 3]
    steps:
      - uses: actions/checkout@v7
      # The image's own Python 3.12 and Node 24: setup-python/setup-node install the runner's toolcache
@@ -50,24 +63,107 @@ jobs:
          "$venv/bin/python" -m pip install --no-cache-dir -r requirements-dev.txt
          echo "$venv/bin" >> "$GITHUB_PATH"
      - run: python --version && node --version && node --version | grep -q '^v24\.'
+      # npm's download cache, keyed on the lockfile; inside the container ~ is the job's HOME (/github/home),
+      # which npm also uses. node_modules itself is still built fresh by npm ci.
+      - name: Cache npm downloads
+        uses: actions/cache@v6
+        with:
+          path: ~/.npm
+          key: npm-${{ runner.os }}-playwright-v1.64.1-${{ hashFiles('tools/vendor/package-lock.json') }}
      - run: npm ci --prefix tools/vendor --ignore-scripts
-      - run: npm run --prefix tools/vendor check
-      - run: npm run --prefix tools/vendor test
-      - name: Frontend unit, viewer, workflow, and coverage checks
-        run: npm run --prefix tools/vendor test:coverage
-      - name: Upload frontend coverage and Chromium traces
+      # Shard 1 also runs the node units and the viewer suite, so the vendor pins and the tooling tests
+      # run on the lightest shard instead.
+      - if: matrix.shard == 3
+        run: npm run --prefix tools/vendor check
+      - if: matrix.shard == 3
+        run: npm run --prefix tools/vendor test
+      - name: Page workflows with coverage, shard ${{ matrix.shard }}/3
+        run: npm run --prefix tools/vendor test:coverage:shard -- ${{ matrix.shard }}/3
+      - name: Upload raw coverage
+        uses: actions/upload-artifact@v7
+        with:
+          name: coverage-raw-${{ matrix.shard }}
+          path: coverage/js/raw/
+          if-no-files-found: error
+          retention-days: 3
+      - name: Upload Chromium and touch traces
+        if: always()
+        uses: actions/upload-artifact@v7
+        with:
+          name: frontend-traces-shard-${{ matrix.shard }}
+          path: tools/vendor/test-results/
+          retention-days: 14
+
+  frontend-coverage-merge:
+    name: frontend coverage (merge)
+    needs: frontend-coverage
+    runs-on: ubuntu-latest
+    # Same image as the shards: the raw files name sources by the container's workspace path.
+    container:
+      image: mcr.microsoft.com/playwright:v1.64.1-noble
+      options: --user 1001
+    timeout-minutes: 10
+    steps:
+      - uses: actions/checkout@v7
+      - run: node --version && node --version | grep -q '^v24\.'
+      # npm's download cache, keyed on the lockfile; inside the container ~ is the job's HOME (/github/home),
+      # which npm also uses. node_modules itself is still built fresh by npm ci.
+      - name: Cache npm downloads
+        uses: actions/cache@v6
+        with:
+          path: ~/.npm
+          key: npm-${{ runner.os }}-playwright-v1.64.1-${{ hashFiles('tools/vendor/package-lock.json') }}
+      - run: npm ci --prefix tools/vendor --ignore-scripts
+      # Each artifact lands in its own coverage-raw-N directory, so the next step can count them.
+      - uses: actions/download-artifact@v8
+        with:
+          pattern: coverage-raw-*
+          path: ${{ runner.temp }}/coverage-raw
+      # coverage:merge only checks that raw files exist; merging two of three shards would report
+      # partial coverage, so a missing or empty shard artifact fails here.
+      - name: Verify every shard's raw coverage arrived
+        shell: bash
+        env:
+          STAGED_RAW: ${{ runner.temp }}/coverage-raw
+          EXPECTED_SHARDS: 3
+        run: |
+          found=0
+          for shard in $(seq 1 "$EXPECTED_SHARDS"); do
+            directory="$STAGED_RAW/coverage-raw-$shard"
+            count=0
+            if [ -d "$directory" ]; then count=$(find "$directory" -maxdepth 1 -type f -name '*.json' | wc -l); fi
+            echo "coverage-raw-$shard: $count raw files"
+            if [ "$count" -gt 0 ]; then found=$((found + 1)); fi
+          done
+          echo "shard artifacts with raw coverage: $found of $EXPECTED_SHARDS"
+          if [ "$found" -ne "$EXPECTED_SHARDS" ]; then
+            echo "::error::Expected raw coverage from $EXPECTED_SHARDS shards, got $found of $EXPECTED_SHARDS"
+            exit 1
+          fi
+          staged=$(find "$STAGED_RAW" -mindepth 2 -maxdepth 2 -type f -name '*.json' | wc -l)
+          mkdir -p coverage/js/raw
+          # cp -n never overwrites; a clash shows up as fewer merged files than staged ones.
+          find "$STAGED_RAW" -mindepth 2 -maxdepth 2 -type f -name '*.json' -exec cp -n -t coverage/js/raw {} + || true
+          merged=$(find coverage/js/raw -maxdepth 1 -type f -name '*.json' | wc -l)
+          if [ "$merged" -ne "$staged" ]; then
+            echo "::error::Shards wrote clashing raw file names: $staged staged, $merged merged"
+            exit 1
+          fi
+          echo "merged $merged raw files"
+      - name: Frontend coverage report and baseline check
+        run: npm run --prefix tools/vendor coverage:merge
+      - name: Upload frontend coverage report
        if: always()
        uses: actions/upload-artifact@v7
        with:
          name: frontend-test-reports
          path: |
-            tools/vendor/test-results/
            coverage/js/
            !coverage/js/raw/**
          retention-days: 14

  browser-workflows:
-    name: page workflows (${{ matrix.browser }})
+    name: page workflows (${{ matrix.browser }}, shard ${{ matrix.shard }}/2)
    runs-on: ubuntu-latest
    # Layout comparisons depend on the fonts each browser falls back to, so browser jobs run in the
    # same pinned Playwright image as local runs (tag = @playwright/test in tools/vendor/package-lock.json;
@@ -75,11 +171,16 @@ jobs:
    container:
      image: mcr.microsoft.com/playwright:v1.64.1-noble
      options: --user 1001
-    timeout-minutes: 25
+    timeout-minutes: 20
+    # Public-repo ubuntu-latest runners have 4 vCPUs: three Playwright workers, each with its own test
+    # server, leave one CPU for the servers and the runner.
+    env:
+      PM_TEST_WORKERS: 3
    strategy:
      fail-fast: false
      matrix:
        browser: [firefox, webkit]
+        shard: [1, 2]
    steps:
      - uses: actions/checkout@v7
      # The image's own Python 3.12 and Node 24: setup-python/setup-node install the runner's toolcache
@@ -98,22 +199,29 @@ jobs:
          "$venv/bin/python" -m pip install --no-cache-dir -r requirements-dev.txt
          echo "$venv/bin" >> "$GITHUB_PATH"
      - run: python --version && node --version && node --version | grep -q '^v24\.'
+      # npm's download cache, keyed on the lockfile; inside the container ~ is the job's HOME (/github/home),
+      # which npm also uses. node_modules itself is still built fresh by npm ci.
+      - name: Cache npm downloads
+        uses: actions/cache@v6
+        with:
+          path: ~/.npm
+          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 }}
-        run: npm run --prefix tools/vendor test:workflows -- --project ${{ matrix.browser }}
+      - name: Page workflows in ${{ matrix.browser }}, shard ${{ matrix.shard }}/2
+        run: npm run --prefix tools/vendor test:workflows -- --project ${{ matrix.browser }} --shard ${{ matrix.shard }}/2
      - name: Upload browser traces
        if: always()
        uses: actions/upload-artifact@v7
        with:
-          name: browser-traces-${{ matrix.browser }}
+          name: browser-traces-${{ matrix.browser }}-shard-${{ matrix.shard }}
          path: tools/vendor/test-results/
          retention-days: 14

  # Branch protection requires the exact context "viewerjs". This job keeps that
-  # name and fails unless every frontend job above succeeded, including when one
-  # was cancelled or skipped.
+  # name and fails unless every frontend job above succeeded (every shard, the
+  # coverage merge and every browser shard), including when one was cancelled or skipped.
  viewerjs:
-    needs: [frontend-coverage, browser-workflows]
+    needs: [frontend-coverage, frontend-coverage-merge, browser-workflows]
    if: always()
    runs-on: ubuntu-latest
    timeout-minutes: 5
@@ -121,8 +229,10 @@ jobs:
      - name: Require every frontend job to succeed
        env:
          COVERAGE_RESULT: ${{ needs.frontend-coverage.result }}
+          MERGE_RESULT: ${{ needs.frontend-coverage-merge.result }}
          WORKFLOWS_RESULT: ${{ needs.browser-workflows.result }}
        run: |
          echo "frontend-coverage: $COVERAGE_RESULT"
+          echo "frontend-coverage-merge: $MERGE_RESULT"
          echo "browser-workflows: $WORKFLOWS_RESULT"
-          test "$COVERAGE_RESULT" = success && test "$WORKFLOWS_RESULT" = success
+          test "$COVERAGE_RESULT" = success && test "$MERGE_RESULT" = success && test "$WORKFLOWS_RESULT" = success
@@ -39,9 +39,44 @@ npm run --prefix tools/vendor test:coverage
 npm run --prefix tools/vendor test:workflows -- --project firefox --project webkit
 ```

-`PM_TEST_PYTHON` selects the Python executable; `PM_TEST_PORT` selects the local
-port (default 8765). Set these environment variables when Python is outside PATH
-or the port is occupied. Test servers are never reused. On unsupported Linux
+`PM_TEST_PYTHON` selects the Python executable; set it when Python is outside
+PATH. Every Playwright worker starts its own `tests/browser/server.py --port 0`,
+which binds a port the OS picks and prints it as `PM_TEST_SERVER_PORT=<n>`, with
+its own temp root and database (`tests/browser/fixtures.mjs`), so
+parallel workers and concurrent runs never share state. `PM_TEST_WORKERS` sets the
+worker count (default 1 under `CI`, otherwise a quarter of the CPUs, at most 8).
+Test servers are never reused across runs. The launcher holds each server's
+stdin open and the server (`--exit-on-stdin-eof`) shuts down cleanly, removing its
+temp root, when that pipe closes, so a worker killed without teardown leaves no
+server behind. A test that fails gets the stderr its server wrote during the test
+attached to the report as `server-stderr` (an aiohttp traceback behind a 500).
+
+The coverage run can be split the way CI splits it, and each shard keeps the raw
+V8 files it writes under `coverage/js/raw`:
+
+```sh
+PM_TEST_WORKERS=8 npm run --prefix tools/vendor test:coverage            # whole run, one report
+npm run --prefix tools/vendor test:coverage:shard -- 1/3                 # node units, viewer suite, workflows 1/3
+npm run --prefix tools/vendor test:coverage:shard -- 2/3                 # workflows 2/3 (likewise 3/3)
+npm run --prefix tools/vendor coverage:merge                             # report and baseline check of every raw file
+npm run --prefix tools/vendor test:workflows -- --project webkit --shard 2/2
+```
+
+`coverage:merge` refuses an empty raw directory; it does not count shards, so run
+every shard first (CI's merge job checks all three arrived). Measured on a 32-CPU
+machine in the pinned image (2026-10-21): `test:coverage` takes about 5 minutes
+with 8 workers and 24 minutes with 1; all four projects, 8 workers, each test 3
+times (6132 tests), 24 minutes. A CI-sized run (`docker run --cpus=4`,
+`PM_TEST_WORKERS=3`, all four projects once, 2044 tests) takes 25.5 minutes.
+
+Specs must pass beside each other, not only alone. Wait for the page's own
+signal, never for time: a rendering frame (`requestAnimationFrame`) for layout
+work queued by a render or a scroll, a response or a visible state for data. A
+timer that "usually" covers a frame is a race on a loaded runner. Library
+virtualization specs settle with `libraryObservation.settled()` (two consecutive
+frames with no Library frame queued). To look for such races, repeat a spec under
+load (`--workers 8 --repeat-each 10`, and in the image with `--cpus=1` or `2`).
+On unsupported Linux
 distributions, browser system dependencies may need manual installation. For a
 quick browser run, use `test:workflows -- --project chromium`.

@@ -114,16 +149,39 @@ second without a browser and fails, naming the files, when a measured
 `web/js` file has no baseline entry or the baseline lists a file that no longer
 exists. It uses the gate's own `discoverSources`, and `npm test` runs the same
 check, so run it before pushing a new or deleted frontend file instead of
-waiting for the `frontend coverage` job.
+waiting for the `frontend coverage` jobs.

 The `viewerjs` check runs on every PR, including backend-only changes. It is an
-aggregate job that passes only when the `frontend coverage (chromium and touch)`
-job and both `page workflows (firefox)` and `page workflows (webkit)` jobs
-succeed; the browsers run on separate runners in parallel. GitHub artifacts
-named `frontend-test-reports` contain HTML coverage, a JSON summary, and the
-Chromium/touch failure screenshots/traces; `browser-traces-firefox` and
-`browser-traces-webkit` hold the other browsers' traces. Open traces with
-Playwright's `show-trace` tool.
+aggregate job that passes only when every frontend job succeeds: the three
+`frontend coverage (shard N/3)` jobs, `frontend coverage (merge)`, and the four
+`page workflows (firefox|webkit, shard N/2)` jobs. A failed, cancelled or skipped
+job fails it. Every browser job runs with `PM_TEST_WORKERS: 3` (the public
+runners have 4 vCPUs). Each coverage shard runs `test:coverage:shard -- N/3`
+(shard 1 also runs the node units and the viewer suite, shard 3 the vendor pins
+and tooling tests) and uploads its raw V8 files as `coverage-raw-N` (kept 3
+days). The merge job downloads them, fails unless all three arrived with raw
+files and without clashing names, then runs `coverage:merge` (report plus
+baseline check). `tests/vendor/ci-workflow.test.mjs` checks this shape. GitHub
+artifacts named `frontend-test-reports` contain the merged HTML coverage and
+JSON summary; `frontend-traces-shard-N` hold the Chromium/touch failure
+screenshots/traces and `browser-traces-<browser>-shard-N` the other browsers'
+traces. Open traces with Playwright's `show-trace` tool.
+
+Every `npm ci` first restores npm's download cache (`~/.npm`), keyed on the vendor
+lockfile and the job's pinned image tag (`tests/vendor/ci-workflow.test.mjs` checks
+the key names the same tag as the job's `container.image`). Without it, `npm ci` stalled for about 300 s
+(npm's fetch timeout) in most of the eight concurrent jobs; with a hit it takes
+0 to 2 s. A lockfile change misses the cache once, so expect one slow run after it.
+Measured on PR #274 (run 39725176320 at cbc8a61, cache hit): the whole workflow
+took 8m38s, against about 33 minutes with one worker and no shards. Jobs: coverage
+shards 7m34s/6m04s/5m22s (tests 6m38s/4m53s/4m04s), merge 54s, firefox shards
+7m57s/5m21s (tests 7m08s/4m34s), webkit shards 8m16s/5m03s (tests 7m26s/3m58s).
+Browser jobs keep a 20-minute limit: the slowest job is about 8.5 minutes, a cache
+miss adds up to 5 to `npm ci`, and runner speed varies (the first sharded run was
+cancelled at a 12-minute limit).
+Playwright shards by test count, whole files at a time, so shard 1 carries the
+slow concept-comparison specs (`*-concept.spec.mjs`, alphabetically first) and
+runs longer; the remedy, if it starts to matter, is more shards, not reordering.

 The real-host suite covers both Classic and Nodes 2.0 startup, switching both
 ways, actual database prompt selection, execution-text serialization, workflow
@@ -1556,7 +1614,7 @@ bytes at the same path without changing the immutable receipt.
 The focused acceptance command retains all four projects:

 ```sh
-PM_TEST_PORT=8766 npm run --prefix tools/vendor test:workflows -- \
+npm run --prefix tools/vendor test:workflows -- \
  workspace-history.spec.mjs workspace-visual.spec.mjs \
  --project chromium --project touch --project firefox --project webkit
 npm run --prefix tools/vendor test:executions
@@ -1649,7 +1707,7 @@ acceptance; a baseline is added only after the maintainer accepts them.
 Focused commands:

 ```sh
-PM_TEST_PORT=8766 npm run --prefix tools/vendor test:workflows -- \
+npm run --prefix tools/vendor test:workflows -- \
  workspace-library-editor.spec.mjs library-editor-visual.spec.mjs \
  --project chromium --project touch --project firefox --project webkit
 npm run --prefix tools/vendor test:comfyui   # library-sender.spec.mjs host regression
@@ -1749,7 +1807,7 @@ mobile, the concept geometry/token/control comparison and its mutation check),

 ```sh
 node --test tests/js/workspace-vocabulary-state.test.js tests/js/workspace-state.test.js
-PM_TEST_PORT=8766 npm run --prefix tools/vendor test:workflows -- \
+npm run --prefix tools/vendor test:workflows -- \
  workspace-vocabulary.spec.mjs vocabulary-visual.spec.mjs focused-node.spec.mjs \
  --project chromium --project touch --project firefox --project webkit
 ```
@@ -1,5 +1,5 @@
 import { startCoverage, saveCoverage } from '../../tools/vendor/browser-coverage.mjs';
-import { test, expect } from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import { test, expect } from './fixtures.mjs';
 import { THEMES, seedConcept, openConcept, openProduction, diffInventory, mutate } from './concept-inventory.mjs';

 // Activity-1 Task 3. The review dialog is compared with the concept's own `scan-review` ("Review metadata scan",
@@ -1,5 +1,5 @@
 import { readFileSync } from 'node:fs';
-import { test, expect } from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import { test, expect } from './fixtures.mjs';
 import { startCoverage, saveCoverage } from '../../tools/vendor/browser-coverage.mjs';

 test.beforeEach(async ({page, browserName}) => {
@@ -57,7 +57,8 @@ test('Classic keeps immediate selection, search query and metadata serialization
 });

 test('Classic detaches native text synchronization on removal',async({page})=>{
-    await page.waitForTimeout(60);
+    // The page installs the text sync (serializeValue and its listeners) in a 50 ms timer; wait for it, not for time.
+    await expect.poll(()=>page.evaluate(()=>typeof node.widgets.find(item=>item.name==='text').serializeValue)).toBe('function');
    const values=await page.evaluate(()=>{
        const widget=node.widgets.find(item=>item.name==='text');
        widget.inputEl.value='Before removal';widget.inputEl.dispatchEvent(new Event('input'));
@@ -2,7 +2,7 @@
 // same concept selectors in the immutable concept (/__test__/canonical/workspace) and in production, which now renders
 // the concept's classes. The concept is never rewritten: each page's map<Page>Concept(reference) applies only the
 // recorded spec-§8 deviations, each commented with its D-number, and diffInventory must then report nothing.
-import {expect} from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import {expect} from './fixtures.mjs';
 export {diffInventory} from './library-editor-canonical-comparison.mjs';

 export const CONCEPT_URL='/__test__/canonical/workspace';
@@ -0,0 +1,33 @@
+// Shared `test` for the page workflows: every Playwright worker owns one
+// tests/browser/server.py process on a port the OS chose for it, with its own temp root
+// and database. `baseURL` (and so `page`, `request` and `browser.newContext`)
+// points at that worker's server. A server that dies fails the running test
+// with its stderr tail, and the next test in the worker gets a fresh server.
+// A test that fails gets the stderr its server wrote during it attached as
+// `server-stderr`.
+import { test as base, expect } from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import { attachServerStderr, createServerSupervisor, startBrowserServer } from '../../tools/vendor/start-browser-server.mjs';
+
+const SERVER_FIXTURE_TIMEOUT_MS = 90_000;
+
+export const test = base.extend({
+    testServer: [async ({}, use) => {
+        const supervisor = createServerSupervisor({ start: () => startBrowserServer() });
+        try {
+            await use(supervisor);
+        } finally {
+            await supervisor.stop();
+        }
+    }, { scope: 'worker', timeout: SERVER_FIXTURE_TIMEOUT_MS }],
+    workerServer: [async ({ testServer }, use, testInfo) => {
+        const server = await testServer.ensure();
+        const mark = server.stderrMark();
+        await use(server);
+        await attachServerStderr(testInfo, server, mark);
+        const crash = testServer.crash(server);
+        if (crash) throw crash;
+    }, { auto: true, timeout: SERVER_FIXTURE_TIMEOUT_MS }],
+    baseURL: async ({ workerServer }, use) => use(workerServer.url),
+});
+
+export { expect };
@@ -1,5 +1,5 @@
 import {readFileSync} from 'node:fs';
-import {test,expect} from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import {test,expect} from './fixtures.mjs';
 import {startCoverage,saveCoverage} from '../../tools/vendor/browser-coverage.mjs';

 for (const variant of ['Focused', 'Split']) {
@@ -1,5 +1,5 @@
 import {startCoverage,saveCoverage} from '../../tools/vendor/browser-coverage.mjs';
-import { test, expect } from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import { test, expect } from './fixtures.mjs';
 import { seedConcept, openConcept, openProduction, SIZES } from './concept-inventory.mjs';
 // D10/D20: the heading is the linked positive's title (its confirmed first line here), never the pair's
 // "Inspector recipe", which names the negative variant.
@@ -1,5 +1,5 @@
 import { writeFile } from 'node:fs/promises';
-import { expect } from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import { expect } from './fixtures.mjs';

 // Content, row counts, and image bytes come from independent synthetic datasets.
 // Saved choices and actual executions are separate production sections. The concept's
@@ -1,5 +1,5 @@
 import {writeFile} from 'node:fs/promises';
-import {test,expect} from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import {test,expect} from './fixtures.mjs';
 import {captureCanonicalState} from './history-canonical-comparison.mjs';
 import {SIZES,THEMES,MOTIONS,seedConcept,openConcept,openProduction,inventoryOf,diffInventory,mutate,stripExact} from './concept-inventory.mjs';

@@ -1,5 +1,5 @@
 import {writeFile} from 'node:fs/promises';
-import {test,expect} from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import {test,expect} from './fixtures.mjs';
 import {captureCanonicalState} from './history-canonical-comparison.mjs';
 import {SIZES,THEMES,MOTIONS,seedConcept,openConcept,openProduction,inventoryOf,diffInventory,mutate,stripExact,countCopy,reflow,withoutItems} from './concept-inventory.mjs';

@@ -1,5 +1,5 @@
 import {writeFile} from 'node:fs/promises';
-import {test,expect} from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import {test,expect} from './fixtures.mjs';
 import {captureCanonicalState} from './history-canonical-comparison.mjs';
 import {SIZES,THEMES,seedConcept,openConcept,openProduction,inspectorOf,diffInventory,mutate,countCopy} from './concept-inventory.mjs';

@@ -1,5 +1,5 @@
 import {writeFile} from 'node:fs/promises';
-import {test,expect} from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import {test,expect} from './fixtures.mjs';
 import {captureCanonicalState} from './history-canonical-comparison.mjs';
 import {SIZES,THEMES,MOTIONS,seedConcept,openConcept,openProduction,inventoryOf,diffInventory,mutate,stripExact,countCopy,reflow} from './concept-inventory.mjs';

@@ -1,4 +1,4 @@
-import {test,expect} from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import {test,expect} from './fixtures.mjs';
 import {captureCanonicalState} from './history-canonical-comparison.mjs';

 // Artifact-only captures of the editor states that have no concept counterpart (archive confirmation, Show archived,
@@ -1,5 +1,5 @@
 import {readFileSync} from 'node:fs';
-import {test,expect} from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import {test,expect} from './fixtures.mjs';
 import {startCoverage,saveCoverage} from '../../tools/vendor/browser-coverage.mjs';

 const pair={id:4,positive_text:'Library positive',negative_text:'Library negative',category:'Portrait',tags:['studio']};
@@ -1,4 +1,4 @@
-import { test, expect } from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import { test, expect } from './fixtures.mjs';
 import { startCoverage, saveCoverage } from '../../tools/vendor/browser-coverage.mjs';

 const moduleUrl = '/prompt_manager/js/shared/toolkit/prompt-bridge.js';
@@ -1,5 +1,5 @@
 import {startCoverage,saveCoverage} from '../../tools/vendor/browser-coverage.mjs';
-import {test,expect} from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import {test,expect} from './fixtures.mjs';

 const workspace='/prompt_manager/workspace#/images';
 const details=page=>page.getByRole('complementary',{name:'Selected image details',exact:true});
@@ -1,16 +1,20 @@
 """Serve production pages and API routes with disposable state for browser tests."""

 import argparse
+import asyncio
 import json
 import os
 import shutil
+import socket
 from pathlib import Path
 import sys
 import tempfile
+import threading
 import time
 import types

 from aiohttp import web
+from aiohttp.web_runner import GracefulExit
 from PIL import Image
 from PIL.PngImagePlugin import PngInfo

@@ -515,14 +519,77 @@ def create_app(root: Path) -> web.Application:
    return app


-def main() -> None:
+HOST = "127.0.0.1"
+PORT_ANNOUNCEMENT = "PM_TEST_SERVER_PORT="
+
+
+def bind_listener(port: int) -> socket.socket:
+    """Bind the server's socket before the app is built.
+
+    ``port`` 0 lets the OS choose a free port, which this process then holds,
+    so parallel launchers never race for one between choosing and binding.
+    """
+    listener = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    try:
+        if port and os.name != "nt":
+            # aiohttp's own default on POSIX; on Windows it would let a
+            # second process share the port.
+            listener.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+        listener.bind((HOST, port))
+        listener.listen(128)
+    except OSError:
+        listener.close()
+        raise
+    return listener
+
+
+def _graceful_exit() -> None:
+    raise GracefulExit()
+
+
+def exit_when_stdin_closes(loop: asyncio.AbstractEventLoop) -> threading.Thread:
+    """Stop the app gracefully once stdin reaches end of file.
+
+    The launcher keeps the write end of this process's stdin pipe, and the OS
+    closes it however the launcher dies, SIGKILL included. GracefulExit runs
+    aiohttp's cleanup (closing the database) and lets the temp root be removed,
+    on every OS, where a signal from a dead parent would not.
+    """
+
+    def watch() -> None:
+        while sys.stdin.buffer.read(65536):
+            pass
+        loop.call_soon_threadsafe(_graceful_exit)
+
+    thread = threading.Thread(target=watch, name="stdin-eof", daemon=True)
+    thread.start()
+    return thread
+
+
+def main(argv: list[str] | None = None) -> None:
    parser = argparse.ArgumentParser()
-    parser.add_argument("--port", type=int, default=8765)
-    args = parser.parse_args()
+    parser.add_argument(
+        "--port", type=int, default=8765, help="0 binds an OS-chosen free port"
+    )
+    parser.add_argument(
+        "--exit-on-stdin-eof",
+        action="store_true",
+        help="shut down when stdin closes (the launcher's parent-death guard)",
+    )
+    args = parser.parse_args(argv)
+    listener = bind_listener(args.port)
+    # One machine-readable line tells the launcher which port this process holds.
+    print(f"{PORT_ANNOUNCEMENT}{listener.getsockname()[1]}", flush=True)
+    loop = asyncio.new_event_loop()
+    if args.exit_on_stdin_eof:
+        exit_when_stdin_closes(loop)
+    original_cwd = os.getcwd()
    with tempfile.TemporaryDirectory(prefix="pm-browser-") as directory:
-        web.run_app(
-            create_app(Path(directory).resolve()), host="127.0.0.1", port=args.port
-        )
+        try:
+            web.run_app(create_app(Path(directory).resolve()), sock=listener, loop=loop)
+        finally:
+            # create_app works inside the root; Windows cannot remove a process's cwd.
+            os.chdir(original_cwd)


 if __name__ == "__main__":
@@ -1,5 +1,5 @@
 import {writeFile} from 'node:fs/promises';
-import {test,expect} from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import {test,expect} from './fixtures.mjs';
 import {captureCanonicalState} from './history-canonical-comparison.mjs';
 import {SIZES,THEMES,MOTIONS,seedConcept,openConcept as openConceptPage,openProduction,inventoryOf,diffInventory,focusRingOf,hoverStateOf,mutate} from './concept-inventory.mjs';

@@ -1,4 +1,4 @@
-import {test,expect} from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import {test,expect} from './fixtures.mjs';
 import {captureCanonicalState} from './history-canonical-comparison.mjs';

 // Artifact-only captures of Tags & categories states that have no concept counterpart: the Manage categories
@@ -0,0 +1,35 @@
+// Each Playwright worker owns its server: `request`, `page` and manual
+// `browser.newContext()` all reach it through `baseURL`, and another server
+// process never sees its database.
+import { test, expect } from './fixtures.mjs';
+import { startBrowserServer } from '../../tools/vendor/start-browser-server.mjs';
+
+const search = text => `/prompt_manager/search?text=${encodeURIComponent(text)}`;
+
+test('every fixture reaches this worker\'s own server and another server keeps its own database', async ({ request, page, browser, baseURL, workerServer }, testInfo) => {
+    expect(baseURL).toBe(workerServer.url);
+    await expect(await request.post('/__test__/reset')).toBeOK();
+    const marker = `worker ${testInfo.workerIndex} isolation ${testInfo.project.name} ${testInfo.repeatEachIndex}`;
+    await expect(await request.post('/prompt_manager/save', { data: { text: marker } })).toBeOK();
+    expect((await (await request.get(search(marker))).json()).count).toBe(1);
+
+    const viaPage = await page.request.get(search(marker));
+    expect(viaPage.url().startsWith(`${baseURL}/`)).toBe(true);
+    expect((await viaPage.json()).count).toBe(1);
+    const context = await browser.newContext();
+    try {
+        const response = await (await context.newPage()).goto(search(marker));
+        expect(response.url().startsWith(`${baseURL}/`)).toBe(true);
+        expect((await response.json()).count).toBe(1);
+    } finally {
+        await context.close();
+    }
+
+    const other = await startBrowserServer();
+    try {
+        expect(other.url).not.toBe(baseURL);
+        expect((await (await fetch(`${other.url}${search(marker)}`)).json()).count).toBe(0);
+    } finally {
+        await other.stop();
+    }
+});
@@ -1,5 +1,5 @@
 import { startCoverage, saveCoverage } from '../../tools/vendor/browser-coverage.mjs';
-import { test, expect } from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import { test, expect } from './fixtures.mjs';

 test.beforeEach(async ({ request, page, browserName }) => {
    await startCoverage(page, browserName);
@@ -64,11 +64,16 @@ test('actual Tags page reloads the selected filter and opens its image viewer',
    await page.goto('/prompt_manager/admin#/tags');
    await page.locator('[data-tag-name="cats"]').click();
    await expect(page.locator('#tagPromptsGrid')).toContainText('Cat portrait');
+    const dogs = page.waitForResponse(response => response.url().includes('/tags/dogs/prompts?'));
    await page.locator('[data-tag-name="dogs"]').click();
+    const [shown] = (await (await dogs).json()).prompts[0].images;
    await expect(page.locator('#tagPromptsGrid')).toContainText('Dog landscape');
    await expect(page.locator('#tagPromptsGrid')).not.toContainText('Cat portrait');
    await page.locator('#tagPromptsGrid img').first().click();
    await expect(page.locator('.viewer-canvas img')).toBeVisible();
+    // The viewer's title names the shown image through the page's title callback. ViewerJS renders it only once the
+    // image is viewed, so closing at "visible" alone left the callback unrun on slower hosts (CI coverage missed it).
+    await expect(page.locator('.viewer-title')).toHaveText(shown.filename);
    await page.locator('.viewer-container').getByRole('button', { name: 'Close', exact: true }).click();
    await expect(page.locator('.viewer-container')).toHaveCount(0);
 });
@@ -1,5 +1,5 @@
 import { startCoverage, saveCoverage } from '../../tools/vendor/browser-coverage.mjs';
-import { test, expect } from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import { test, expect } from './fixtures.mjs';
 import { seedConcept, openConcept, openProduction } from './concept-inventory.mjs';

 // Activity (#249 Activity-1): the concept's Activity page (app.js renderActivity 732–738), its top-bar button
@@ -1,5 +1,5 @@
 import {startCoverage,saveCoverage} from '../../tools/vendor/browser-coverage.mjs';
-import {test,expect} from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import {test,expect} from './fixtures.mjs';
 import {readFile,writeFile} from 'node:fs/promises';
 import {createHash} from 'node:crypto';

@@ -1,5 +1,5 @@
 import { startCoverage, saveCoverage } from '../../tools/vendor/browser-coverage.mjs';
-import { test, expect } from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import { test, expect } from './fixtures.mjs';
 import { seedConcept, openConcept, openProduction } from './concept-inventory.mjs';

 const workspace = '/prompt_manager/workspace#/images';
@@ -1,6 +1,6 @@
 import {writeFile} from 'node:fs/promises';
 import {startCoverage,saveCoverage} from '../../tools/vendor/browser-coverage.mjs';
-import {test,expect} from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import {test,expect} from './fixtures.mjs';
 import {captureCanonicalState} from './history-canonical-comparison.mjs';
 import {inventoryOf,mapConcept,diffInventory} from './library-editor-canonical-comparison.mjs';

@@ -1,5 +1,5 @@
 import {startCoverage,saveCoverage} from '../../tools/vendor/browser-coverage.mjs';
-import {test,expect} from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import {test,expect} from './fixtures.mjs';

 const route='/prompt_manager/workspace#/library';
 const cards=page=>page.locator('article[data-prompt-id]');
@@ -25,6 +25,8 @@ async function loadShelfPages(page,more,pages) {
        await more.evaluate(node=>node.click());await response;await expect(more).toHaveAttribute('aria-disabled','false');
    }
 }
+/** Resolves in the rendering frame after every frame callback the page had already queued (callbacks run in request order). */
+const nextFrame=page=>page.evaluate(()=>new Promise(resolve=>requestAnimationFrame(()=>resolve())));
 async function openHistory(page,text='Cat portrait') {
    await cards(page).filter({has:page.getByText(text,{exact:true})}).getByRole('button',{name:'Explore history',exact:true}).click();
    await expect(history(page)).toBeVisible();
@@ -103,7 +105,8 @@ test('library infinite loading keeps unique parents and keyboard-accessible hist
        const appended=await (await nextPage).json();expect(appended.items.length).toBeGreaterThan(0);hasMore=appended.has_more;
        if(hasMore)await expect(more).toHaveAttribute('aria-disabled','false');
    }
-    await expect(more).toBeHidden();expect(await cards(page).count()).toBeLessThan(80);
+    // The last page's render queued the window update for the next frame; count after that frame, not before it.
+    await expect(more).toBeHidden();await nextFrame(page);expect(await cards(page).count()).toBeLessThan(80);
    const ids=await cards(page).evaluateAll(nodes=>nodes.map(node=>node.dataset.promptId));expect(new Set(ids).size).toBe(ids.length);
    await expect(page.getByRole('button',{name:/next page|previous page/i})).toHaveCount(0);
    const firstId=await cards(page).first().getAttribute('data-prompt-id');
@@ -376,14 +379,18 @@ async function observeLibrary(page, hold=false) {
            holdFrames(){holdingFrames=true;},
            releaseFrames(){holdingFrames=false;const callbacks=[...heldFrames.values()];heldFrames.clear();for(const callback of callbacks)callback();},
            equal(){for(const record of records){const entries=[...record.latest.values()].filter(entry=>record.targets.has(entry.target));if(entries.length)record.callback(entries,record.native);}},
+            // Resolves once two consecutive rendering frames find no Library frame queued. Each check runs inside a native
+            // frame callback, so a frame the page queues later in that update (a scroll event, a ResizeObserver delivery) is
+            // still pending there. A timer is not a frame: under CPU load a 60 ms wait could end before the scroll's frame.
+            // A frame that never drains (a rAF loop, or settling while frames are held) fails after `limit` frames with the stats.
+            settled(limit=600){return new Promise((resolve,reject)=>{let quiet=0,frames=0;const check=()=>{frames++;quiet=pending.size?0:quiet+1;
+                if(quiet>=2)resolve();else if(frames>=limit)reject(new Error(`Library never settled within ${limit} frames: ${JSON.stringify(window.libraryObservation.stats())}`));else raf(check);};raf(check);});},
            stats(){return {requested,pending:pending.size,heldFrames:heldFrames.size,measurements:records.reduce((sum,record)=>sum+record.entries.size,0),mutations,unmounted,targets:records.reduce((sum,record)=>sum+record.targets.size,0)};},
        };
    },{hold});
 }
 async function settleLibrary(page) {
-    await expect.poll(async()=>page.evaluate(()=>window.libraryObservation.stats().pending)).toBe(0);
-    await page.evaluate(()=>new Promise(resolve=>setTimeout(resolve,60)));
-    await expect.poll(async()=>page.evaluate(()=>window.libraryObservation.stats().pending)).toBe(0);
+    await page.evaluate(()=>window.libraryObservation.settled());
 }
 async function firstVisibleParent(page) {
    return cards(page).evaluateAll(nodes=>{
@@ -683,6 +690,17 @@ test('title and Explore history are buttons that open history',async({page,reque
    await page.keyboard.press('ArrowLeft');await expect(cards(page).nth(1).locator('.card-title > button')).toBeFocused();
 });

+test('settling fails with the observation stats when a Library frame stays queued',async({page,request})=>{
+    await request.post('/__test__/reset',{data:{native_library:true,extra_prompts:200}});
+    await observeLibrary(page);await page.addInitScript(()=>{window.IntersectionObserver=undefined;});
+    await page.goto(route);await expect(cards(page).first()).toBeVisible();await settleLibrary(page);
+    await page.evaluate(()=>{window.libraryObservation.holdFrames();dispatchEvent(new Event('scroll'));});
+    await expect.poll(()=>page.evaluate(()=>window.libraryObservation.stats().heldFrames)).toBeGreaterThan(0);
+    const failure=await page.evaluate(()=>window.libraryObservation.settled(30).then(()=>'settled',error=>error.message));
+    expect(failure).toMatch(/^Library never settled within 30 frames: \{.*"heldFrames":[1-9]/);
+    await page.evaluate(()=>window.libraryObservation.releaseFrames());await settleLibrary(page);
+});
+
 test('virtualized rows keep measured heights with the clamp',async({page,request,isMobile})=>{
    await request.post('/__test__/reset',{data:{native_library:true,extra_prompts:200}});
    await observeLibrary(page);await page.addInitScript(()=>{window.IntersectionObserver=undefined;});
@@ -1,5 +1,5 @@
 import { startCoverage, saveCoverage } from '../../tools/vendor/browser-coverage.mjs';
-import { test, expect } from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import { test, expect } from './fixtures.mjs';

 // Saved views (#249 D16, maintainer ruling 2026-10-21): the toolbar's Save view (concept app.js a359, a1330–1346),
 // the sidebar SAVED VIEWS rows (a331–335) and `#/saved/<id>` (a1158–1162), on Images and the Prompt library.
@@ -3,7 +3,7 @@ import { readFile } from 'node:fs/promises';
 import { createHash } from 'node:crypto';
 import { captureCanonicalState, historyGeometry, compareCanonicalHistory, nativeDialogState, exerciseCurrentPairSend, assertRecordedHistory } from './history-canonical-comparison.mjs';
 import { startCoverage, saveCoverage } from '../../tools/vendor/browser-coverage.mjs';
-import { test, expect } from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import { test, expect } from './fixtures.mjs';

 test.use({ locale: 'en-US', timezoneId: 'UTC', reducedMotion: 'reduce' });
 const workspace = '/prompt_manager/workspace';
@@ -1,6 +1,6 @@
 import {startCoverage,saveCoverage} from '../../tools/vendor/browser-coverage.mjs';
 import {writeFile} from 'node:fs/promises';
-import {test,expect} from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import {test,expect} from './fixtures.mjs';
 import {captureCanonicalState} from './history-canonical-comparison.mjs';
 import {pageInventoryOf,inventoryOf,diffInventory,mapVocabularyConcept,mapVocabularyDialog} from './vocabulary-canonical-comparison.mjs';

@@ -1,5 +1,5 @@
 import { startCoverage, saveCoverage } from '../../tools/vendor/browser-coverage.mjs';
-import { test, expect } from '../../tools/vendor/node_modules/@playwright/test/index.mjs';
+import { test, expect } from './fixtures.mjs';

 const workspace = '/prompt_manager/workspace';
 const statistic = (page, label) => page.locator('#workspace-main dt')
@@ -0,0 +1,83 @@
+"""The page-workflow test server ends with its launcher (#274 review M2).
+
+A Playwright worker that is SIGKILLed never runs its fixture teardown, so the
+server it started must notice on its own: with ``--exit-on-stdin-eof`` it shuts
+down when the launcher's end of its stdin pipe closes, and still removes its
+temp root. This runs on every OS in CI, where Windows is the strict case.
+"""
+
+import os
+import subprocess
+import sys
+import tempfile
+import time
+import unittest
+import urllib.request
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).resolve().parent.parent
+SERVER_TIMEOUT_S = 60
+
+
+class TestBrowserServerLifetime(unittest.TestCase):
+    def setUp(self):
+        self.tmp = tempfile.TemporaryDirectory()
+        self.addCleanup(self.tmp.cleanup)
+
+    def start(self, *extra):
+        env = {**os.environ, "TMPDIR": self.tmp.name}
+        env.update(TEMP=self.tmp.name, TMP=self.tmp.name)
+        process = subprocess.Popen(
+            [sys.executable, "-m", "tests.browser.server", "--port", "0", *extra],
+            cwd=REPO_ROOT,
+            env=env,
+            stdin=subprocess.PIPE,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+        )
+
+        def stop():
+            if process.poll() is None:
+                process.kill()
+            process.wait(timeout=SERVER_TIMEOUT_S)
+            # communicate() would flush a closed stdin, which Python < 3.13 refuses.
+            for stream in (process.stdin, process.stdout, process.stderr):
+                stream.close()
+
+        self.addCleanup(stop)
+        line = process.stdout.readline().decode()
+        self.assertTrue(line.startswith("PM_TEST_SERVER_PORT="), line)
+        url = f"http://127.0.0.1:{int(line.split('=', 1)[1])}/prompt_manager/test"
+        deadline = time.monotonic() + SERVER_TIMEOUT_S
+        while True:
+            try:
+                with urllib.request.urlopen(url, timeout=1) as response:  # nosec B310
+                    self.assertEqual(response.status, 200)
+                return process
+            except OSError:
+                self.assertIsNone(process.poll(), "the server exited early")
+                self.assertLess(time.monotonic(), deadline, "never ready")
+                time.sleep(0.1)
+
+    def roots(self):
+        return sorted(path.name for path in Path(self.tmp.name).glob("pm-browser-*"))
+
+    def test_server_exits_and_removes_its_temp_root_when_stdin_closes(self):
+        process = self.start("--exit-on-stdin-eof")
+        self.assertEqual(len(self.roots()), 1, "the server works in its own temp root")
+        process.stdin.close()
+        code = process.wait(timeout=SERVER_TIMEOUT_S)
+        self.assertEqual(
+            code, 0, process.stderr.read().decode(errors="replace")[-4000:]
+        )
+        self.assertEqual(self.roots(), [], "the temp root and its database are removed")
+
+    def test_server_keeps_running_with_stdin_closed_without_the_flag(self):
+        process = self.start()
+        process.stdin.close()
+        with self.assertRaises(subprocess.TimeoutExpired):
+            process.wait(timeout=1)
+
+
+if __name__ == "__main__":
+    unittest.main()
@@ -0,0 +1,234 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { createServer } from 'node:net';
+import { spawn } from 'node:child_process';
+import { once } from 'node:events';
+import { readFileSync } from 'node:fs';
+import { fileURLToPath, pathToFileURL } from 'node:url';
+import { setTimeout as delay } from 'node:timers/promises';
+import { startBrowserServer, createServerSupervisor, attachServerStderr } from '../../tools/vendor/start-browser-server.mjs';
+import { workflowWorkers } from '../../tools/vendor/test-workers.mjs';
+
+const fakeServer = fileURLToPath(new URL('./fake-browser-server.mjs', import.meta.url));
+const fake = (...extra) => ({ command: process.execPath, args: port => [fakeServer, '--port', String(port), ...extra] });
+const REAL_SERVER_TIMEOUT_MS = 90_000;
+const launcher = fileURLToPath(new URL('../../tools/vendor/start-browser-server.mjs', import.meta.url));
+
+/** Polls `check` until it is truthy, failing with `what` after `ms`. */
+async function waitFor(check, what, ms = 5_000) {
+    const deadline = Date.now() + ms;
+    while (!check()) {
+        if (Date.now() > deadline) throw new Error(`timed out waiting for ${what}`);
+        await delay(20);
+    }
+}
+
+async function writeStderr(server, text) {
+    await (await fetch(`${server.url}/__stderr?text=${encodeURIComponent(text)}`)).text();
+    await waitFor(() => server.stderrTail().endsWith(text.trimEnd()), `stderr ${JSON.stringify(text)}`);
+}
+
+/** A process that exited counts as gone even while a non-reaping PID 1 (CI's container) leaves it a zombie. */
+function alive(pid) {
+    try { process.kill(pid, 0); } catch { return false; }
+    try { return readFileSync(`/proc/${pid}/stat`, 'utf8').replace(/^.*\) /s, '')[0] !== 'Z'; } catch { return true; }
+}
+
+/** Starts a server from a separate Node worker process, SIGKILLs that worker and returns the server's pid. */
+async function serverOfKilledWorker(options) {
+    const script = `import { startBrowserServer } from ${JSON.stringify(pathToFileURL(launcher).href)};
+        const server = await startBrowserServer(${options});
+        console.log('SERVER_PID=' + server.pid);
+        setInterval(() => {}, 1000);`;
+    const worker = spawn(process.execPath, ['--input-type=module', '-e', script], { stdio: ['ignore', 'pipe', 'inherit'] });
+    let out = '';
+    worker.stdout.setEncoding('utf8');
+    worker.stdout.on('data', chunk => { out += chunk; });
+    await waitFor(() => /SERVER_PID=\d+\n/.test(out) || worker.exitCode !== null, 'the worker to start its server', REAL_SERVER_TIMEOUT_MS);
+    const pid = Number(/SERVER_PID=(\d+)/.exec(out)?.[1]);
+    assert.ok(pid > 0, `the worker started a server (output: ${out})`);
+    assert.ok(alive(pid), 'the server runs while its worker lives');
+    worker.kill('SIGKILL');
+    await once(worker, 'exit');
+    return pid;
+}
+
+function listen(port = 0) {
+    return new Promise((resolve, reject) => {
+        const server = createServer();
+        server.once('error', reject);
+        server.listen(port, '127.0.0.1', () => resolve(server));
+    });
+}
+
+async function releasedPort() {
+    const probe = await listen();
+    const { port } = probe.address();
+    await new Promise(resolve => probe.close(resolve));
+    return port;
+}
+
+test('free port allocation never reuses a bound port', async t => {
+    const held = await listen();
+    t.after(() => held.close());
+    const heldPort = held.address().port;
+    const servers = await Promise.all(Array.from({ length: 6 }, () => startBrowserServer(fake())));
+    t.after(() => Promise.all(servers.map(server => server.stop())));
+    const ports = servers.map(server => server.port);
+    for (const server of servers) {
+        assert.ok(Number.isInteger(server.port) && server.port > 0 && server.port < 65536, `port ${server.port} is a TCP port`);
+        assert.equal(server.url, `http://127.0.0.1:${server.port}`);
+        assert.equal(await (await fetch(`${server.url}/prompt_manager/test`)).text(), 'ready');
+    }
+    assert.ok(!ports.includes(heldPort), 'a port another process holds is never handed out');
+    assert.equal(new Set(ports).size, ports.length, 'concurrent servers never share a port');
+});
+
+test('startBrowserServer asks the server to bind port 0 and reads the port it announces', async () => {
+    const asked = [];
+    const server = await startBrowserServer({ command: process.execPath, args: port => { asked.push(port); return fake().args(port); } });
+    try {
+        assert.deepEqual(asked, [0], 'no port is reserved and released before the server binds');
+        assert.ok(server.port > 0);
+    } finally {
+        await server.stop();
+    }
+});
+
+test('startBrowserServer serves the readiness page on a requested port and stops cleanly', async () => {
+    const port = await releasedPort();
+    const server = await startBrowserServer({ port, ...fake() });
+    assert.equal(server.port, port);
+    assert.equal(server.url, `http://127.0.0.1:${port}`);
+    assert.equal(await (await fetch(`${server.url}/prompt_manager/test`)).text(), 'ready');
+    await server.stop();
+    await assert.rejects(fetch(`${server.url}/prompt_manager/test`));
+});
+
+test('startBrowserServer reports a startup failure with the server\'s stderr tail', async () => {
+    await assert.rejects(startBrowserServer(fake('--fail')), error => {
+        assert.match(error.message, /exited with code 4 before it was ready/);
+        assert.match(error.message, /last fake stderr line/);
+        return true;
+    });
+});
+
+test('startBrowserServer gives up on a server that never announces a port or becomes ready', async () => {
+    const silent = { command: process.execPath, args: () => ['-e', 'setInterval(() => {}, 1000)'] };
+    await assert.rejects(startBrowserServer({ ...silent, timeoutMs: 500 }), /not ready .* within 500 ms/);
+});
+
+test('worker server restarts after an unexpected exit', async t => {
+    const supervisor = createServerSupervisor({ start: () => startBrowserServer(fake()) });
+    t.after(() => supervisor.stop());
+    const first = await supervisor.ensure();
+    assert.equal(supervisor.crash(first), null, 'a running server reports no crash');
+    await fetch(`${first.url}/__exit`);
+    await first.exited;
+    const crash = supervisor.crash(first);
+    assert.match(crash.message, /test server on port \d+ exited unexpectedly \(code 3\)/);
+    assert.match(crash.message, /crashed on purpose/);
+    const second = await supervisor.ensure();
+    assert.notEqual(second, first, 'the next test gets a fresh server');
+    assert.equal(await (await fetch(`${second.url}/prompt_manager/test`)).text(), 'ready');
+    assert.equal(await supervisor.ensure(), second, 'a healthy server is reused');
+});
+
+test('supervisor reports a startup failure once and tries again on the next ensure', async t => {
+    let attempts = 0;
+    const supervisor = createServerSupervisor({
+        start: async () => {
+            attempts += 1;
+            if (attempts === 1) throw new Error('ImportError: no module');
+            return startBrowserServer(fake());
+        },
+    });
+    t.after(() => supervisor.stop());
+    await assert.rejects(supervisor.ensure(), /ImportError/);
+    assert.equal(attempts, 1, 'a failed startup is not retried behind the caller\'s back');
+    const server = await supervisor.ensure();
+    assert.equal(attempts, 2);
+    assert.equal(await (await fetch(`${server.url}/prompt_manager/test`)).text(), 'ready');
+});
+
+test('the port announcement counts only once its line is complete', async t => {
+    const server = await startBrowserServer({ ...fake('--split-announce'), timeoutMs: 5_000 });
+    t.after(() => server.stop());
+    assert.equal(await (await fetch(`${server.url}/prompt_manager/test`)).text(), 'ready');
+    assert.equal(server.url, `http://127.0.0.1:${server.port}`);
+});
+
+test('server stderr since a mark holds only what came after it, bounded to the newest output', async t => {
+    const server = await startBrowserServer({ ...fake(), stderrLogChars: 64 });
+    t.after(() => server.stop());
+    await writeStderr(server, 'earlier test\n');
+    const mark = server.stderrMark();
+    assert.equal(server.stderrSince(mark), '');
+    await writeStderr(server, 'Traceback: this test\n');
+    assert.equal(server.stderrSince(mark), 'Traceback: this test\n');
+    const flood = `${'x'.repeat(80)}newest\n`;
+    await writeStderr(server, flood);
+    const kept = server.stderrSince(mark);
+    assert.match(kept, /^\[earlier server stderr dropped\]\n/);
+    assert.ok(kept.endsWith('newest\n'), 'the newest output is kept');
+    assert.ok(kept.length <= 64 + '[earlier server stderr dropped]\n'.length, `bounded, got ${kept.length} chars`);
+});
+
+test('a failed test gets the server stderr written during it attached; a passing one does not', async t => {
+    const server = await startBrowserServer(fake());
+    t.after(() => server.stop());
+    const attached = [];
+    const info = status => ({ status, expectedStatus: 'passed', attach: async (name, options) => { attached.push({ name, ...options }); } });
+    await writeStderr(server, 'before the test\n');
+    const mark = server.stderrMark();
+    await attachServerStderr(info('failed'), server, mark);
+    assert.deepEqual(attached, [], 'nothing to attach when the server wrote nothing');
+    await writeStderr(server, 'Traceback (most recent call last): boom\n');
+    await attachServerStderr(info('passed'), server, mark);
+    assert.deepEqual(attached, [], 'a passing test attaches nothing');
+    await attachServerStderr(info('timedOut'), server, mark);
+    assert.equal(attached.length, 1);
+    assert.equal(attached[0].name, 'server-stderr');
+    assert.equal(attached[0].contentType, 'text/plain');
+    assert.equal(String(attached[0].body), 'Traceback (most recent call last): boom\n');
+});
+
+test('a server exits with its worker even when the worker is SIGKILLed', async () => {
+    const pid = await serverOfKilledWorker(`{ command: process.execPath, args: port => [${JSON.stringify(fakeServer)}, '--port', String(port), '--exit-on-stdin-eof'] }`);
+    await waitFor(() => !alive(pid), `server ${pid} to exit after its worker died`);
+});
+
+test('tests/browser/server.py exits with a SIGKILLed worker', { timeout: 2 * REAL_SERVER_TIMEOUT_MS }, async () => {
+    const pid = await serverOfKilledWorker(`{ timeoutMs: ${REAL_SERVER_TIMEOUT_MS} }`);
+    await waitFor(() => !alive(pid), `server.py ${pid} to exit after its worker died`, 15_000);
+});
+
+test('tests/browser/server.py binds an OS-chosen port for --port 0 and still honours --port N', { timeout: 2 * REAL_SERVER_TIMEOUT_MS }, async t => {
+    const held = await listen();
+    t.after(() => held.close());
+    const chosen = await startBrowserServer({ timeoutMs: REAL_SERVER_TIMEOUT_MS });
+    try {
+        assert.notEqual(chosen.port, held.address().port);
+        assert.equal((await fetch(`${chosen.url}/prompt_manager/test`)).status, 200);
+    } finally {
+        await chosen.stop();
+    }
+    const port = await releasedPort();
+    const fixed = await startBrowserServer({ port, timeoutMs: REAL_SERVER_TIMEOUT_MS });
+    try {
+        assert.equal(fixed.port, port);
+        assert.equal((await fetch(`http://127.0.0.1:${port}/prompt_manager/test`)).status, 200);
+    } finally {
+        await fixed.stop();
+    }
+});
+
+test('worker count follows PM_TEST_WORKERS, then one in CI, then a quarter of the CPUs up to eight', () => {
+    assert.equal(workflowWorkers({ env: { PM_TEST_WORKERS: '3', CI: '1' }, cpus: 32 }), 3);
+    assert.equal(workflowWorkers({ env: { CI: '1' }, cpus: 32 }), 1);
+    assert.equal(workflowWorkers({ env: {}, cpus: 32 }), 8);
+    assert.equal(workflowWorkers({ env: {}, cpus: 12 }), 3);
+    assert.equal(workflowWorkers({ env: {}, cpus: 2 }), 1);
+    assert.throws(() => workflowWorkers({ env: { PM_TEST_WORKERS: 'many' }, cpus: 8 }), /PM_TEST_WORKERS must be a positive integer/);
+    assert.throws(() => workflowWorkers({ env: { PM_TEST_WORKERS: '0' }, cpus: 8 }), /PM_TEST_WORKERS must be a positive integer/);
+});
@@ -0,0 +1,223 @@
+// Structural checks on .github/workflows/viewerjs-check.yml. The tooling has no YAML parser, so these
+// read the workflow's fixed two-space layout: jobs at two spaces, their keys at four, steps at six.
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { execFileSync } from 'node:child_process';
+import { mkdtemp, mkdir, readdir, rm, writeFile } from 'node:fs/promises';
+import { readFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+
+const workflow = readFileSync(new URL('../../.github/workflows/viewerjs-check.yml', import.meta.url), 'utf8');
+const PINNED_IMAGE = /^\s+image: mcr\.microsoft\.com\/playwright:v\d+\.\d+\.\d+-noble$/m;
+
+function jobs(text) {
+    const lines = text.split('\n');
+    const start = lines.indexOf('jobs:');
+    assert.notEqual(start, -1, 'workflow has a jobs section');
+    const found = new Map();
+    let current = null;
+    for (const line of lines.slice(start + 1)) {
+        const header = /^ {2}([\w-]+):\s*$/.exec(line);
+        if (header) {
+            current = header[1];
+            found.set(current, []);
+        } else if (current && (line.startsWith('    ') || line.trim() === '' || /^ {2}#/.test(line))) {
+            found.get(current).push(line);
+        } else if (current && /^\S/.test(line)) {
+            break;
+        }
+    }
+    return new Map([...found].map(([id, body]) => [id, body.join('\n')]));
+}
+
+function steps(jobText) {
+    const parts = jobText.split(/^(?= {6}- )/m);
+    return parts.slice(1);
+}
+
+function runScript(stepText) {
+    const lines = stepText.split('\n');
+    const index = lines.findIndex(line => /^ {8}run: \|\s*$/.test(line));
+    assert.notEqual(index, -1, 'step has a block run script');
+    const body = [];
+    for (const line of lines.slice(index + 1)) {
+        if (line.trim() !== '' && !line.startsWith('          ')) break;
+        body.push(line.slice(10));
+    }
+    return body.join('\n');
+}
+
+function needsOf(jobText) {
+    const match = /^ {4}needs: \[([^\]]*)\]\s*$/m.exec(jobText) ?? /^ {4}needs: ([\w-]+)\s*$/m.exec(jobText);
+    assert.ok(match, 'job declares needs');
+    return match[1].split(',').map(value => value.trim()).filter(Boolean);
+}
+
+function matrixList(jobText, key) {
+    const match = new RegExp(`^ {8}${key}: \\[([^\\]]*)\\]\\s*$`, 'm').exec(jobText);
+    assert.ok(match, `job has a ${key} matrix`);
+    return match[1].split(',').map(value => value.trim());
+}
+
+const allJobs = jobs(workflow);
+const browserJobIds = [...allJobs].filter(([, body]) => /npm run --prefix tools\/vendor test:(workflows|coverage)/.test(body))
+    .map(([id]) => id);
+const mergeJob = () => allJobs.get('frontend-coverage-merge');
+const verifyStep = () => steps(mergeJob()).find(step => /name: Verify every shard's raw coverage arrived/.test(step));
+
+test('viewerjs keeps its name and needs every frontend job', () => {
+    const viewerjs = allJobs.get('viewerjs');
+    assert.ok(viewerjs, 'the required context is the job id viewerjs');
+    assert.doesNotMatch(viewerjs, /^ {4}name:/m, 'no display name may replace the context "viewerjs"');
+    const needs = needsOf(viewerjs);
+    const others = [...allJobs.keys()].filter(id => id !== 'viewerjs');
+    assert.deepEqual([...needs].sort(), [...others].sort(), 'viewerjs needs every other job in the workflow');
+    assert.deepEqual([...needs].sort(), ['browser-workflows', 'frontend-coverage', 'frontend-coverage-merge']);
+    assert.match(viewerjs, /^ {4}if: always\(\)$/m, 'viewerjs runs (and fails) when a needed job failed or was skipped');
+    const script = runScript(steps(viewerjs).find(step => /run: \|/.test(step)));
+    for (const id of needs) {
+        const variable = new RegExp(`^ {10}([A-Z_]+): \\$\\{\\{ needs\\.${id}\\.result \\}\\}$`, 'm').exec(viewerjs);
+        assert.ok(variable, `${id}'s result reaches the check`);
+        assert.match(script, new RegExp(`test "\\$${variable[1]}" = success`), `${id} must be exactly success`);
+    }
+});
+
+test('viewerjs fails unless every needed job succeeded', () => {
+    const viewerjs = allJobs.get('viewerjs');
+    const script = runScript(steps(viewerjs).find(step => /run: \|/.test(step)));
+    const variables = [...viewerjs.matchAll(/^ {10}([A-Z_]+): \$\{\{ needs\.[\w-]+\.result \}\}$/gm)].map(match => match[1]);
+    const run = env => {
+        try {
+            execFileSync('bash', ['--noprofile', '--norc', '-eo', 'pipefail', '-c', script], { env: { PATH: process.env.PATH, ...env }, stdio: 'pipe' });
+            return true;
+        } catch {
+            return false;
+        }
+    };
+    const allSuccess = Object.fromEntries(variables.map(name => [name, 'success']));
+    assert.equal(run(allSuccess), true);
+    for (const name of variables) {
+        for (const result of ['failure', 'cancelled', 'skipped']) {
+            assert.equal(run({ ...allSuccess, [name]: result }), false, `${name}=${result} must fail viewerjs`);
+        }
+    }
+});
+
+test('coverage runs as three shards that each upload their raw coverage', () => {
+    const coverage = allJobs.get('frontend-coverage');
+    assert.deepEqual(matrixList(coverage, 'shard'), ['1', '2', '3']);
+    assert.match(coverage, /^ {4}name: frontend coverage \(shard \$\{\{ matrix\.shard \}\}\/3\)$/m);
+    assert.match(coverage, /npm run --prefix tools\/vendor test:coverage:shard -- \$\{\{ matrix\.shard \}\}\/3/);
+    const upload = steps(coverage).find(step => /name: coverage-raw-\$\{\{ matrix\.shard \}\}/.test(step));
+    assert.ok(upload, 'each shard uploads coverage-raw-N');
+    assert.match(upload, /^ {10}path: coverage\/js\/raw\/?$/m);
+    assert.match(upload, /^ {10}retention-days: 3$/m);
+    assert.match(upload, /^ {10}if-no-files-found: error$/m);
+});
+
+test('merge job downloads every shard and runs the merge-only report and check', () => {
+    const merge = mergeJob();
+    assert.ok(merge, 'frontend-coverage-merge exists');
+    assert.deepEqual(needsOf(merge), ['frontend-coverage']);
+    assert.match(merge, /^ {4}name: frontend coverage \(merge\)$/m);
+    const download = steps(merge).find(step => /uses: actions\/download-artifact@/.test(step));
+    assert.ok(download, 'merge downloads the shard artifacts');
+    assert.match(download, /^ {10}pattern: coverage-raw-\*$/m);
+    assert.doesNotMatch(download, /merge-multiple: true/, 'each artifact keeps its own directory so the check can count them');
+    assert.ok(verifyStep(), 'merge has an explicit artifact count check');
+    assert.match(verifyStep(), new RegExp(`^ {10}EXPECTED_SHARDS: ${matrixList(allJobs.get('frontend-coverage'), 'shard').length}$`, 'm'),
+        'the expected count matches the shard matrix');
+    const order = steps(merge).map(step => (/name: (.*)/.exec(step) ?? [, step.trim().split('\n')[0]])[1]);
+    const verifyAt = order.findIndex(name => /Verify every shard/.test(name));
+    const mergeAt = steps(merge).findIndex(step => /npm run --prefix tools\/vendor coverage:merge/.test(step));
+    assert.ok(verifyAt >= 0 && mergeAt > verifyAt, 'the count check runs before coverage:merge');
+    const report = steps(merge).find(step => /name: frontend-test-reports$/m.test(step));
+    assert.ok(report, 'merge uploads the HTML report as frontend-test-reports');
+    assert.match(report, /!coverage\/js\/raw\/\*\*/);
+});
+
+async function stagedShards(root, shards) {
+    const staged = join(root, 'staged');
+    for (const [shard, files] of shards) {
+        const directory = join(staged, `coverage-raw-${shard}`);
+        await mkdir(directory, { recursive: true });
+        for (const file of files) await writeFile(join(directory, file), '{"result":[]}');
+    }
+    await mkdir(staged, { recursive: true });
+    return staged;
+}
+
+async function verify(t, shards) {
+    const root = await mkdtemp(join(tmpdir(), 'pm-ci-merge-'));
+    t.after(() => rm(root, { recursive: true, force: true }));
+    const staged = await stagedShards(root, shards);
+    try {
+        execFileSync('bash', ['--noprofile', '--norc', '-eo', 'pipefail', '-c', runScript(verifyStep())], {
+            cwd: root, stdio: 'pipe',
+            env: { PATH: process.env.PATH, STAGED_RAW: staged, EXPECTED_SHARDS: '3' },
+        });
+    } catch (error) {
+        return { ok: false, output: `${error.stdout}${error.stderr}` };
+    }
+    return { ok: true, raw: (await readdir(join(root, 'coverage/js/raw'))).sort() };
+}
+
+test('merge refuses when a shard\'s raw coverage is missing', async t => {
+    const missing = await verify(t, [[1, ['a.json']], [3, ['c.json']]]);
+    assert.equal(missing.ok, false);
+    assert.match(missing.output, /2 of 3/);
+    const empty = await verify(t, [[1, ['a.json']], [2, []], [3, ['c.json']]]);
+    assert.equal(empty.ok, false, 'an artifact without raw files counts as missing');
+    const collision = await verify(t, [[1, ['a.json']], [2, ['a.json']], [3, ['c.json']]]);
+    assert.equal(collision.ok, false, 'two shards writing the same file name must not silently drop one');
+    const complete = await verify(t, [[1, ['a.json', 'node.json']], [2, ['b.json']], [3, ['c.json']]]);
+    assert.deepEqual(complete, { ok: true, raw: ['a.json', 'b.json', 'c.json', 'node.json'] });
+});
+
+test('every browser job sets PM_TEST_WORKERS and runs in the pinned image', () => {
+    assert.deepEqual([...browserJobIds].sort(), ['browser-workflows', 'frontend-coverage']);
+    for (const id of browserJobIds) {
+        const body = allJobs.get(id);
+        assert.match(body, /^ {6}PM_TEST_WORKERS: 3$/m, `${id} sets PM_TEST_WORKERS for the whole job`);
+        assert.match(body, PINNED_IMAGE, `${id} keeps the pinned Playwright image`);
+        assert.match(body, /PIP_SHA256: [0-9a-f]{64}/, `${id} keeps the pinned pip bootstrap`);
+        assert.match(body, /^ {4}timeout-minutes: \d+$/m);
+    }
+    assert.match(mergeJob(), PINNED_IMAGE, 'the merge sees the same workspace paths as the shards');
+});
+
+test('page workflows run each browser in two shards', () => {
+    const workflows = allJobs.get('browser-workflows');
+    assert.deepEqual(matrixList(workflows, 'browser'), ['firefox', 'webkit']);
+    assert.deepEqual(matrixList(workflows, 'shard'), ['1', '2']);
+    assert.match(workflows, /test:workflows -- --project \$\{\{ matrix\.browser \}\} --shard \$\{\{ matrix\.shard \}\}\/2/);
+    assert.match(workflows, /^ {6}fail-fast: false$/m);
+    assert.match(workflows, /name: browser-traces-\$\{\{ matrix\.browser \}\}-shard-\$\{\{ matrix\.shard \}\}/);
+});
+
+test('every npm ci restores the npm download cache keyed on the vendor lockfile first', () => {
+    const installing = [...allJobs].filter(([, body]) => /npm ci --prefix tools\/vendor/.test(body));
+    assert.deepEqual(installing.map(([id]) => id).sort(), ['browser-workflows', 'frontend-coverage', 'frontend-coverage-merge']);
+    for (const [id, body] of installing) {
+        const jobSteps = steps(body);
+        const cacheAt = jobSteps.findIndex(step => /uses: actions\/cache@v\d+/.test(step));
+        const installAt = jobSteps.findIndex(step => /npm ci --prefix tools\/vendor/.test(step));
+        assert.ok(cacheAt >= 0 && cacheAt < installAt, `${id} restores the npm cache before npm ci`);
+        assert.match(jobSteps[cacheAt], /^ {10}path: ~\/\.npm$/m, `${id} caches npm's download cache, not node_modules`);
+        assert.match(jobSteps[cacheAt], /hashFiles\('tools\/vendor\/package-lock\.json'\)/, `${id} keys the cache on the lockfile`);
+        assert.match(jobSteps[installAt], /npm ci --prefix tools\/vendor --ignore-scripts/, `${id} still installs without scripts`);
+        // The key names the job's own pinned image, so an image bump starts a fresh cache.
+        const image = /^ {6}image: mcr\.microsoft\.com\/playwright:(v\d+\.\d+\.\d+)-noble$/m.exec(body)?.[1];
+        assert.ok(image, `${id} runs in the pinned Playwright image`);
+        assert.match(jobSteps[cacheAt], new RegExp(`key: npm-\\$\\{\\{ runner\\.os \\}\\}-playwright-${image.replaceAll('.', '\\.')}-\\$\\{\\{ hashFiles`),
+            `${id} keys the cache on its image ${image}`);
+    }
+});
+
+test('browser job timeouts keep a real margin over measured runs', () => {
+    for (const id of ['frontend-coverage', 'browser-workflows']) {
+        const minutes = Number(/^ {4}timeout-minutes: (\d+)$/m.exec(allJobs.get(id))[1]);
+        assert.ok(minutes >= 20, `${id} allows at least 20 minutes, since runner speed varies`);
+    }
+});
@@ -0,0 +1,44 @@
+// A stand-in for tests/browser/server.py: `--port N` (0 = an OS-chosen port)
+// serves the readiness page and announces the bound port on stdout as
+// `PM_TEST_SERVER_PORT=<n>`, `--fail` writes to stderr and exits before
+// listening, and GET /__exit makes the process die unexpectedly after writing a
+// last stderr line. GET /__stderr?text=T writes T to stderr before answering.
+// `--split-announce` writes the announcement in two chunks, the first ending
+// mid-number. `--exit-on-stdin-eof` exits when its stdin closes, as server.py does.
+import { createServer } from 'node:http';
+
+const args = process.argv.slice(2);
+const port = Number(args[args.indexOf('--port') + 1]);
+if (args.includes('--fail')) {
+    process.stderr.write('fake server: refusing to start\nlast fake stderr line\n');
+    process.exit(4);
+}
+const server = createServer((request, response) => {
+    const url = new URL(request.url, 'http://fake');
+    if (url.pathname === '/__stderr') {
+        process.stderr.write(url.searchParams.get('text'));
+        response.end('written');
+        return;
+    }
+    if (request.url === '/__exit') {
+        process.stderr.write('fake server: crashed on purpose\n');
+        response.end('bye', () => process.exit(3));
+        return;
+    }
+    response.end(request.url === '/prompt_manager/test' ? 'ready' : `pid ${process.pid}`);
+});
+server.listen(port, '127.0.0.1', () => {
+    const line = `PM_TEST_SERVER_PORT=${server.address().port}\n`;
+    if (!args.includes('--split-announce')) {
+        process.stdout.write(`fake server: listening\n${line}`);
+        return;
+    }
+    // The first chunk is a complete-looking number, one digit short of the real port.
+    process.stdout.write(`fake server: listening\n${line.slice(0, -2)}`);
+    setTimeout(() => process.stdout.write(line.slice(-2)), 300);
+});
+if (args.includes('--exit-on-stdin-eof')) {
+    process.stdin.resume();
+    process.stdin.once('end', () => process.exit(0));
+}
+for (const signal of ['SIGTERM', 'SIGINT']) process.once(signal, () => server.close(() => process.exit(0)));
@@ -0,0 +1,93 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { existsSync, mkdtempSync, mkdirSync, rmSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { plan, runCoverage } from '../../tools/vendor/frontend-coverage.mjs';
+
+const steps = argv => plan(argv).map(({ step, ...options }) => (Object.keys(options).length ? { step, ...options } : step));
+
+function tempPaths(t) {
+    const root = mkdtempSync(join(tmpdir(), 'pm-coverage-cli-'));
+    t.after(() => rmSync(root, { recursive: true, force: true }));
+    const reportRoot = join(root, 'coverage/js');
+    return { root, paths: { repositoryRoot: root, tools: join(root, 'tools'), reportRoot, raw: join(reportRoot, 'raw'), sourceRoot: join(root, 'web/js') } };
+}
+
+function recorder() {
+    const calls = [];
+    const run = (args, env = {}) => { calls.push({ args, env }); };
+    return { calls, run };
+}
+
+test('no arguments plans the unchanged full run', () => {
+    assert.deepEqual(steps([]), [
+        'clean', 'node-units', 'viewer', { step: 'workflows', shard: null }, 'report', { step: 'check', updateBaseline: false },
+    ]);
+    assert.deepEqual(steps(['--update-baseline']), [
+        'clean', 'node-units', 'viewer', { step: 'workflows', shard: null }, 'report', { step: 'check', updateBaseline: true },
+    ]);
+});
+
+test('--shard 2/3 plans only workflows with --shard 2/3 and no report', () => {
+    assert.deepEqual(steps(['--shard', '2/3']), ['prepare', { step: 'workflows', shard: '2/3' }]);
+    assert.deepEqual(steps(['--shard=3/3']), ['prepare', { step: 'workflows', shard: '3/3' }]);
+});
+
+test('--shard 1/N also runs the node units and the viewer suite', () => {
+    assert.deepEqual(steps(['--shard', '1/3']), ['prepare', 'node-units', 'viewer', { step: 'workflows', shard: '1/3' }]);
+    assert.deepEqual(steps(['--shard', '1/1']), ['prepare', 'node-units', 'viewer', { step: 'workflows', shard: '1/1' }]);
+});
+
+test('--merge-only plans the report and the check over existing raw coverage', () => {
+    assert.deepEqual(steps(['--merge-only']), ['require-raw', 'report', { step: 'check', updateBaseline: false }]);
+    assert.deepEqual(steps(['--merge-only', '--update-baseline']), ['require-raw', 'report', { step: 'check', updateBaseline: true }]);
+});
+
+test('invalid shard and mode combinations are refused', () => {
+    for (const argv of [['--shard'], ['--shard', '0/3'], ['--shard', '4/3'], ['--shard', '2'], ['--shard', 'a/b'], ['--shard', '1/0'], ['--shard', '1.5/3']]) {
+        assert.throws(() => plan(argv), /--shard needs I\/N/, argv.join(' '));
+    }
+    assert.throws(() => plan(['--shard', '1/2', '--merge-only']), /either --shard or --merge-only/);
+    assert.throws(() => plan(['--shard', '1/2', '--update-baseline']), /--update-baseline .* --merge-only or a full run/);
+    assert.throws(() => plan(['--shard', '1/2', '--shard', '2/2']), /--shard once/);
+    assert.throws(() => plan(['--report']), /Unknown argument: --report/);
+});
+
+test('--merge-only refuses an empty raw dir', async t => {
+    const { paths } = tempPaths(t);
+    const { calls, run } = recorder();
+    await assert.rejects(runCoverage({ argv: ['--merge-only'], run, paths }), /no raw coverage .*coverage\/js\/raw.* run the --shard steps first/i);
+    mkdirSync(paths.raw, { recursive: true });
+    await assert.rejects(runCoverage({ argv: ['--merge-only'], run, paths }), /no raw coverage/i);
+    writeFileSync(join(paths.raw, 'notes.txt'), 'not coverage');
+    await assert.rejects(runCoverage({ argv: ['--merge-only'], run, paths }), /no raw coverage/i);
+    assert.deepEqual(calls, [], 'nothing is reported or checked over partial or empty coverage');
+});
+
+test('a shard keeps raw coverage other shards wrote and passes its shard to Playwright', async t => {
+    const { paths } = tempPaths(t);
+    mkdirSync(paths.raw, { recursive: true });
+    const earlier = join(paths.raw, 'browser-earlier-shard.json');
+    writeFileSync(earlier, '{"result":[]}');
+    const { calls, run } = recorder();
+    await runCoverage({ argv: ['--shard', '2/3'], run, paths });
+    assert.ok(existsSync(earlier), 'raw files from another shard survive');
+    assert.equal(calls.length, 1, 'shard 2 runs only the workflows');
+    const [{ args, env }] = calls;
+    assert.deepEqual(args.slice(-6), ['--project', 'chromium', '--project', 'touch', '--shard', '2/3']);
+    assert.equal(env.PM_JS_COVERAGE, paths.raw);
+});
+
+test('shard 1 runs the node units into the shared raw dir, then the viewer suite, then its workflows', async t => {
+    const { root, paths } = tempPaths(t);
+    mkdirSync(join(root, 'tests/js'), { recursive: true });
+    writeFileSync(join(root, 'tests/js/a.test.js'), '');
+    const { calls, run } = recorder();
+    await runCoverage({ argv: ['--shard', '1/3'], run, paths });
+    assert.equal(calls.length, 3);
+    assert.deepEqual(calls[0].args, ['--test', 'tests/js/a.test.js']);
+    assert.equal(calls[0].env.NODE_V8_COVERAGE, paths.raw);
+    assert.ok(calls[1].args.includes(join(paths.tools, 'playwright.config.mjs')));
+    assert.deepEqual(calls[2].args.slice(-2), ['--shard', '1/3']);
+});
@@ -1,4 +1,4 @@
-import { readFileSync, readdirSync, mkdirSync, rmSync, writeFileSync } from 'node:fs';
+import { existsSync, readFileSync, readdirSync, mkdirSync, rmSync, writeFileSync } from 'node:fs';
 import { dirname, join, relative } from 'node:path';
 import { fileURLToPath, pathToFileURL } from 'node:url';
 import { spawnSync } from 'node:child_process';
@@ -7,33 +7,69 @@ import { repositoryRoot } from './vendor-viewerjs.mjs';
 import { discoverSources, checkCoverage } from '@comfyassets/toolkit/testing/coverage';
 export { discoverSources, checkCoverage };
 const metrics = ['lines', 'branches', 'functions', 'statements'];
+const SHARD = /^([1-9]\d*)\/([1-9]\d*)$/;
+const USAGE = 'usage: frontend-coverage.mjs [--update-baseline] | --shard I/N | --merge-only [--update-baseline]';

-function run(args, env = {}) {
+function runNode(args, env = {}) {
    const result = spawnSync(process.execPath, args, { cwd: repositoryRoot, stdio: 'inherit',
        env: { ...process.env, ...env } });
    if (result.status !== 0) throw new Error(`Command failed (${result.status}): ${args.join(' ')}`);
 }

-async function main() {
-    const tools = dirname(fileURLToPath(import.meta.url));
+function defaultPaths() {
    const reportRoot = join(repositoryRoot, 'coverage/js');
-    const raw = join(reportRoot, 'raw');
-    const sourceRoot = join(repositoryRoot, 'web/js');
+    return { repositoryRoot, tools: dirname(fileURLToPath(import.meta.url)), reportRoot,
+        raw: join(reportRoot, 'raw'), sourceRoot: join(repositoryRoot, 'web/js') };
+}
+
+function parseShard(value) {
+    const match = SHARD.exec(value ?? '');
+    if (!match || Number(match[1]) > Number(match[2])) {
+        throw new Error(`--shard needs I/N with 1 <= I <= N, got ${value ?? 'nothing'}\n${USAGE}`);
+    }
+    return { index: Number(match[1]), total: Number(match[2]), value };
+}
+
+// Turn the command line into the ordered steps of one coverage run:
+// - no mode: the full run (clean, node units, viewer suite, chromium+touch
+//   workflows, report, check), exactly as before shards existed;
+// - --shard I/N: one slice of the workflows into coverage/js/raw, without wiping
+//   it or reporting; shard 1 also runs the node units and the viewer suite;
+// - --merge-only: report and check over raw coverage the shards already wrote.
+export function plan(argv) {
+    let shard = null;
+    let mergeOnly = false;
+    let updateBaseline = false;
+    for (let index = 0; index < argv.length; index += 1) {
+        const arg = argv[index];
+        if (arg === '--update-baseline') updateBaseline = true;
+        else if (arg === '--merge-only') mergeOnly = true;
+        else if (arg === '--shard' || arg.startsWith('--shard=')) {
+            if (shard) throw new Error(`Pass --shard once\n${USAGE}`);
+            shard = parseShard(arg === '--shard' ? argv[(index += 1)] : arg.slice('--shard='.length));
+        } else throw new Error(`Unknown argument: ${arg}\n${USAGE}`);
+    }
+    if (shard && mergeOnly) throw new Error(`Pass either --shard or --merge-only\n${USAGE}`);
+    if (shard && updateBaseline) throw new Error(`--update-baseline needs --merge-only or a full run, not a shard\n${USAGE}`);
+    const check = { step: 'check', updateBaseline };
+    if (mergeOnly) return [{ step: 'require-raw' }, { step: 'report' }, check];
+    if (shard) {
+        const first = shard.index === 1 ? [{ step: 'node-units' }, { step: 'viewer' }] : [];
+        return [{ step: 'prepare' }, ...first, { step: 'workflows', shard: shard.value }];
+    }
+    return [{ step: 'clean' }, { step: 'node-units' }, { step: 'viewer' }, { step: 'workflows', shard: null },
+        { step: 'report' }, check];
+}
+
+function rawCoverageFiles(raw) {
+    return existsSync(raw) ? readdirSync(raw).filter(file => file.endsWith('.json')) : [];
+}
+
+function checkSummary({ tools, reportRoot, sourceRoot }, updateBaseline) {
    const files = discoverSources(sourceRoot);
-    rmSync(reportRoot, { recursive: true, force: true });
-    mkdirSync(raw, { recursive: true });
-    const tests = readdirSync(join(repositoryRoot, 'tests/js')).filter(file => file.endsWith('.test.js')).map(file => `tests/js/${file}`);
-    run(['--test', ...tests], { NODE_V8_COVERAGE: raw });
-    const playwright = join(tools, 'node_modules/@playwright/test/cli.js');
-    run([playwright, 'test', '--config', join(tools, 'playwright.config.mjs')]);
-    run([playwright, 'test', '--config', join(tools, 'playwright.workflows.config.mjs'),
-        '--project', 'chromium', '--project', 'touch'], { PM_JS_COVERAGE: raw });
-    run([join(tools, 'node_modules/c8/bin/c8.js'), 'report', '--all', '--src', sourceRoot,
-        '--include', 'web/js/**/*.js', '--include', 'web/js/**/*.mjs', '--temp-directory', raw, '--reports-dir', reportRoot,
-        '--reporter', 'text', '--reporter', 'json-summary', '--reporter', 'html']);
    const summary = JSON.parse(readFileSync(join(reportRoot, 'coverage-summary.json'), 'utf8'));
    const baselinePath = join(tools, 'frontend-coverage-baseline.json');
-    if (process.argv.includes('--update-baseline')) {
+    if (updateBaseline) {
        const previous = JSON.parse(readFileSync(baselinePath, 'utf8'));
        const failures = checkCoverage(summary, previous, sourceRoot, files.filter(file => previous[file]));
        if (failures.length) throw new Error(`Baseline updates cannot lower coverage:\n${failures.join('\n')}`);
@@ -53,8 +89,51 @@ async function main() {
        const failures = checkCoverage(summary, baseline, sourceRoot, files);
        if (failures.length) throw new Error(`Frontend coverage regressed:\n${failures.join('\n')}`);
    }
-    console.log(`Frontend coverage passed for ${files.length} files. Report: ${relative(repositoryRoot, reportRoot)}/index.html`);
+    return files.length;
 }
+
+export async function runCoverage({ argv = process.argv.slice(2), run = runNode, paths = defaultPaths() } = {}) {
+    const { repositoryRoot: root, tools, reportRoot, raw, sourceRoot } = paths;
+    const playwright = join(tools, 'node_modules/@playwright/test/cli.js');
+    const actions = {
+        clean() {
+            rmSync(reportRoot, { recursive: true, force: true });
+            mkdirSync(raw, { recursive: true });
+        },
+        prepare() {
+            mkdirSync(raw, { recursive: true });
+        },
+        'require-raw'() {
+            if (!rawCoverageFiles(raw).length) {
+                throw new Error(`No raw coverage in ${relative(root, raw) || raw}: run the --shard steps first, `
+                    + 'or put every shard\'s raw files there');
+            }
+        },
+        'node-units'() {
+            const tests = readdirSync(join(root, 'tests/js')).filter(file => file.endsWith('.test.js'))
+                .map(file => `tests/js/${file}`);
+            run(['--test', ...tests], { NODE_V8_COVERAGE: raw });
+        },
+        viewer() {
+            run([playwright, 'test', '--config', join(tools, 'playwright.config.mjs')]);
+        },
+        workflows({ shard }) {
+            run([playwright, 'test', '--config', join(tools, 'playwright.workflows.config.mjs'),
+                '--project', 'chromium', '--project', 'touch', ...(shard ? ['--shard', shard] : [])], { PM_JS_COVERAGE: raw });
+        },
+        report() {
+            run([join(tools, 'node_modules/c8/bin/c8.js'), 'report', '--all', '--src', sourceRoot,
+                '--include', 'web/js/**/*.js', '--include', 'web/js/**/*.mjs', '--temp-directory', raw, '--reports-dir', reportRoot,
+                '--reporter', 'text', '--reporter', 'json-summary', '--reporter', 'html']);
+        },
+        check({ updateBaseline }) {
+            const count = checkSummary(paths, updateBaseline);
+            console.log(`Frontend coverage passed for ${count} files. Report: ${relative(root, reportRoot)}/index.html`);
+        },
+    };
+    for (const { step, ...options } of plan(argv)) await actions[step](options);
+}
+
 if (process.argv[1] && import.meta.url === pathToFileURL(process.argv[1]).href) {
-    main().catch(error => { console.error(error.message); process.exitCode = 1; });
+    runCoverage().catch(error => { console.error(error.message); process.exitCode = 1; });
 }
@@ -15,6 +15,8 @@
    "test:comfyui": "playwright test --config comfyui.config.mjs",
    "test:executions": "playwright test --config playwright.execution.config.mjs",
    "test:coverage": "node frontend-coverage.mjs",
+    "test:coverage:shard": "node frontend-coverage.mjs --shard",
+    "coverage:merge": "node frontend-coverage.mjs --merge-only",
    "coverage:baseline-check": "node coverage-baseline-check.mjs",
    "coverage:update": "node frontend-coverage.mjs --update-baseline",
    "test:compat": "playwright test --config pack-compat.config.mjs"
@@ -1,23 +1,18 @@
 import { defineConfig, devices } from '@playwright/test';
-import { repositoryRoot } from './vendor-viewerjs.mjs';
-const port = Number(process.env.PM_TEST_PORT || 8765);
+import { workflowWorkers } from './test-workers.mjs';
+
+// No global webServer: tests/browser/fixtures.mjs starts one server per worker
+// on an OS-chosen port. Files run in parallel; tests inside a file keep their order.
 export default defineConfig({
    testDir: '../../tests/browser',
    outputDir: './test-results/workflows',
    testMatch: '*.spec.mjs',
-    workers: 1,
+    workers: workflowWorkers(),
    fullyParallel: false,
    forbidOnly: Boolean(process.env.CI),
    retries: 0,
    reporter: 'list',
-    use: { baseURL: `http://127.0.0.1:${port}`, trace: 'retain-on-failure', screenshot: 'only-on-failure' },
-    webServer: {
-        command: `node tools/vendor/start-browser-server.mjs --port ${port}`,
-        cwd: repositoryRoot,
-        url: `http://127.0.0.1:${port}/prompt_manager/test`,
-        reuseExistingServer: false,
-        gracefulShutdown: { signal: 'SIGTERM', timeout: 5000 },
-    },
+    use: { trace: 'retain-on-failure', screenshot: 'only-on-failure' },
    projects: [
        { name: 'chromium', outputDir: './test-results/workflows/chromium', use: { browserName: 'chromium' } },
        { name: 'firefox', outputDir: './test-results/workflows/firefox', use: { browserName: 'firefox' } },
@@ -1,8 +1,189 @@
 import { spawn } from 'node:child_process';
-const child = spawn(process.env.PM_TEST_PYTHON || 'python',
-    ['-m', 'tests.browser.server', ...process.argv.slice(2)], { stdio: 'inherit' });
-child.on('error', error => { console.error(error.message); process.exitCode = 1; });
-child.on('exit', code => { process.exitCode = code ?? 1; });
-for (const signal of ['SIGTERM', 'SIGINT']) {
-    process.once(signal, () => child.kill(signal));
+import { resolve } from 'node:path';
+import { pathToFileURL } from 'node:url';
+import { setTimeout as delay } from 'node:timers/promises';
+import { repositoryRoot } from './vendor-viewerjs.mjs';
+
+const READY_PATH = '/prompt_manager/test';
+const STARTUP_TIMEOUT_MS = 60_000;
+const STOP_TIMEOUT_MS = 5_000;
+const POLL_INTERVAL_MS = 100;
+const PROBE_TIMEOUT_MS = 1_000;
+const STDERR_TAIL_BYTES = 8_192;
+// Server stderr kept for the failing test's attachment; the newest output wins.
+const STDERR_LOG_CHARS = 256 * 1024;
+const STDERR_DROPPED = '[earlier server stderr dropped]\n';
+const HOST = '127.0.0.1';
+// tests/browser/server.py prints this once it holds its listening socket. Only a
+// complete line counts: a chunk may end mid-number.
+const PORT_ANNOUNCEMENT = /^PM_TEST_SERVER_PORT=(\d+)\r?\n/m;
+
+// The server exits when its stdin closes, so a worker that dies without teardown
+// (SIGKILL) leaves no server behind; the launcher holds the pipe's other end.
+const pythonServer = port => ['-m', 'tests.browser.server', '--port', String(port), '--exit-on-stdin-eof'];
+
+function describeExit({ code, signal }) {
+    return signal ? `signal ${signal}` : `code ${code}`;
+}
+
+// Start one disposable tests/browser/server.py and wait until it serves the
+// readiness page. `port` 0 (the default) lets the server bind an OS-chosen port
+// itself and announce it on stdout, so nothing can take the port between
+// choosing and binding. Resolves to {port, url, exited, exitStatus,
+// pid, stderrTail(), stderrMark(), stderrSince(mark), stop()}; rejects with the
+// server's stderr tail when it exits or stays unready. stdin is a pipe this
+// process holds open for the server's life.
+export async function startBrowserServer({
+    port = 0,
+    command = process.env.PM_TEST_PYTHON || 'python',
+    args = pythonServer,
+    cwd = repositoryRoot,
+    timeoutMs = STARTUP_TIMEOUT_MS,
+    stderrLogChars = STDERR_LOG_CHARS,
+} = {}) {
+    if (!Number.isInteger(port) || port < 0 || port > 65535) {
+        throw new Error(`startBrowserServer needs a port from 0 to 65535, got ${port}`);
+    }
+    const child = spawn(command, args(port), { cwd, stdio: ['pipe', 'pipe', 'pipe'] });
+    // Never written; closing it (or this process dying) tells the server to exit.
+    child.stdin.on('error', () => {});
+    let stderr = '';
+    let stderrTotal = 0;
+    child.stderr.setEncoding('utf8');
+    child.stderr.on('data', chunk => {
+        stderr = (stderr + chunk).slice(-Math.max(stderrLogChars, STDERR_TAIL_BYTES));
+        stderrTotal += chunk.length;
+    });
+    let stdout = '';
+    let announced = null;
+    child.stdout.setEncoding('utf8');
+    // Keep draining stdout for the server's whole life so it never blocks on a full pipe.
+    child.stdout.on('data', chunk => {
+        if (announced !== null) return;
+        stdout = (stdout + chunk).slice(-STDERR_TAIL_BYTES);
+        const match = PORT_ANNOUNCEMENT.exec(stdout);
+        if (match) announced = Number(match[1]);
+    });
+    const killOnExit = () => child.kill('SIGKILL');
+    process.once('exit', killOnExit);
+    const server = {
+        pid: child.pid,
+        port: port || null,
+        url: port ? `http://${HOST}:${port}` : null,
+        exitStatus: null,
+        stopping: false,
+        stderrTail: () => stderr.slice(-STDERR_TAIL_BYTES).trimEnd(),
+        // A position in the server's stderr stream, for stderrSince().
+        stderrMark: () => stderrTotal,
+        // What the server wrote after `mark`, at most stderrLogChars of the newest of it.
+        stderrSince(mark) {
+            const kept = Math.min(stderr.length, stderrLogChars);
+            const keptFrom = stderrTotal - kept;
+            const log = stderr.slice(stderr.length - kept);
+            return mark >= keptFrom ? log.slice(mark - keptFrom) : STDERR_DROPPED + log;
+        },
+        exited: new Promise(done => {
+            child.once('error', error => {
+                stderr += `\n${error.message}`;
+                server.exitStatus = { code: null, signal: null, error };
+                done(server.exitStatus);
+            });
+            child.once('exit', (code, signal) => {
+                server.exitStatus = { code, signal };
+                done(server.exitStatus);
+            });
+        }),
+        async stop() {
+            server.stopping = true;
+            child.stdin.destroy();
+            if (server.exitStatus === null) {
+                child.kill('SIGTERM');
+                const stopped = await Promise.race([server.exited, delay(STOP_TIMEOUT_MS).then(() => false)]);
+                if (!stopped) {
+                    child.kill('SIGKILL');
+                    await server.exited;
+                }
+            }
+            process.removeListener('exit', killOnExit);
+        },
+    };
+    server.exited.then(() => process.removeListener('exit', killOnExit));
+    const failure = async reason => {
+        await server.stop();
+        const tail = server.stderrTail();
+        return new Error(`test server on port ${server.port ?? '(not yet announced)'} ${reason}`
+            + (tail ? `\n--- server stderr tail ---\n${tail}` : ''));
+    };
+    const deadline = Date.now() + timeoutMs;
+    while (Date.now() < deadline) {
+        if (server.exitStatus !== null) {
+            throw await failure(`exited with ${describeExit(server.exitStatus)} before it was ready`);
+        }
+        if (announced !== null && server.url === null) {
+            server.port = announced;
+            server.url = `http://${HOST}:${announced}`;
+        }
+        if (announced !== null && announced !== server.port) {
+            throw await failure(`announced port ${announced} instead`);
+        }
+        if (server.url === null) {
+            await delay(POLL_INTERVAL_MS);
+            continue;
+        }
+        try {
+            const response = await fetch(`${server.url}${READY_PATH}`, { signal: AbortSignal.timeout(PROBE_TIMEOUT_MS) });
+            await response.arrayBuffer();
+            if (response.ok) return server;
+        } catch {
+            // Not listening yet.
+        }
+        await delay(POLL_INTERVAL_MS);
+    }
+    throw await failure(`was not ready at ${READY_PATH} within ${timeoutMs} ms`);
+}
+
+// After a test: when it did not end as expected, attach what the server wrote to
+// stderr since `mark` (an aiohttp traceback names the cause a "got 500" hides).
+export async function attachServerStderr(testInfo, server, mark) {
+    if (testInfo.status === testInfo.expectedStatus) return;
+    const log = server.stderrSince(mark);
+    if (log) await testInfo.attach('server-stderr', { body: log, contentType: 'text/plain' });
+}
+
+// Keep one live server for a Playwright worker. ensure() returns the running
+// server, or starts a fresh one when the last one died (a failed start is
+// reported, not retried); crash(server) turns an unexpected exit into an error
+// carrying the stderr tail.
+export function createServerSupervisor({ start }) {
+    let current = null;
+    return {
+        async ensure() {
+            if (current && current.exitStatus === null) return current;
+            current = null;
+            current = await start();
+            return current;
+        },
+        crash(server) {
+            if (!server || server.stopping || server.exitStatus === null) return null;
+            const tail = server.stderrTail();
+            return new Error(`test server on port ${server.port} exited unexpectedly (${describeExit(server.exitStatus)})`
+                + (tail ? `\n--- server stderr tail ---\n${tail}` : ''));
+        },
+        async stop() {
+            const server = current;
+            current = null;
+            await server?.stop();
+        },
+    };
+}
+
+// CLI: `node start-browser-server.mjs --port N` runs one server in the foreground.
+if (process.argv[1] && import.meta.url === pathToFileURL(resolve(process.argv[1])).href) {
+    const child = spawn(process.env.PM_TEST_PYTHON || 'python',
+        ['-m', 'tests.browser.server', ...process.argv.slice(2)], { stdio: 'inherit' });
+    child.on('error', error => { console.error(error.message); process.exitCode = 1; });
+    child.on('exit', code => { process.exitCode = code ?? 1; });
+    for (const signal of ['SIGTERM', 'SIGINT']) {
+        process.once(signal, () => child.kill(signal));
+    }
 }
@@ -0,0 +1,18 @@
+import { availableParallelism } from 'node:os';
+
+const MAX_LOCAL_WORKERS = 8;
+const CPUS_PER_WORKER = 4;
+
+// PM_TEST_WORKERS wins; CI without it keeps one worker, so CI only changes
+// through explicit workflow edits; locally a quarter of the CPUs, at most eight.
+export function workflowWorkers({ env = process.env, cpus = availableParallelism() } = {}) {
+    if (env.PM_TEST_WORKERS !== undefined) {
+        const workers = Number(env.PM_TEST_WORKERS);
+        if (!Number.isInteger(workers) || workers < 1) {
+            throw new Error(`PM_TEST_WORKERS must be a positive integer, got "${env.PM_TEST_WORKERS}"`);
+        }
+        return workers;
+    }
+    if (env.CI) return 1;
+    return Math.max(1, Math.min(MAX_LOCAL_WORKERS, Math.floor(cpus / CPUS_PER_WORKER)));
+}
Author	SHA1	Message	Date
Vito Sansevero	82ec8782b4	fix(browser): server shutdown and its tests on Windows, Python < 3.13 and CI Three CI failures on `ed809f7`: - Windows: server.py exited 1 on stdin EOF because create_app works with the temp root as its cwd, and Windows cannot remove a process's cwd. main() now restores the original cwd before the root is removed. - Python 3.10 to 3.12: the lifetime test's cleanup called communicate() after closing stdin, which flushes the closed pipe (ValueError); 3.13 tolerates it. It now waits and closes the pipes itself, and the exit assertion shows the server's stderr. Under 3.12: errors=2 before, OK after. - Tooling (CI container): the SIGKILLed-worker tests treated an exited server as alive, because the container's PID 1 does not reap orphans and kill(pid, 0) succeeds on a zombie. Reproduced locally with docker without --init (2 failed); a zombie now counts as exited (2 passed).	2026-10-21 22:57:03 -07:00
Vito Sansevero	14cfb8aedf	docs(testing): server lifetime, stderr attachments and the final measured CI times TESTING.md describes the stdin-EOF shutdown and the server-stderr attachment, states that the npm cache key names the job's image tag (now tested), quotes run 39725176320 at `cbc8a61` (8m38s) and explains the 20-minute browser job limit. The workflow timing comment quotes the same run.	2026-10-21 22:37:49 -07:00
Vito Sansevero	ed809f7fa4	test(browser): server stderr on failures, no orphan servers, waits on state Final review fixes for the per-worker test servers (#274): - A failed test gets the stderr its server wrote during that test attached as `server-stderr`, so an aiohttp traceback behind a 500 reaches the CI report. The launcher keeps the newest 256 KB with a stream position per test (stderrMark/stderrSince), and the fixture attaches it only when the test did not end as expected. - The port announcement counts only as a complete line; a chunk ending mid-number was read as a shorter port. - server.py --exit-on-stdin-eof shuts down gracefully (database closed, temp root removed) when stdin closes. The launcher holds that pipe, so a SIGKILLed worker leaves no server behind, on every OS. - settled() gives up after 600 frames with the observation stats instead of hanging to the test timeout. - The Classic text-sync test waits for the page's 50 ms timer to install serializeValue instead of sleeping 60 ms. With that timer run 100 ms late (a scratch copy), the old wait failed 20/20 and the poll passed 20/20; the spec passed 240/240 at 8 workers x10 and 240/240 at 1 CPU with 4 workers. - The workflow test checks each npm cache key names its job's pinned image tag. Every new unit test failed before its change (missing export, the old regex timing out on the split announcement, an unknown server flag, a hung settle, a mismatched cache key).	2026-10-21 22:37:48 -07:00
Vito Sansevero	cbc8a61b1d	test(browser): stable under parallel workers Document how to run the browser suites in parallel and sharded, with the measured times, and what keeps specs stable beside each other: wait for a rendering frame, a response or a visible state, never for time. With `b665aa6` the full workflows suite passed on chromium, touch, firefox and webkit with 8 workers, each test 3 times (6132 passed, 0 failed, 24 minutes), and once at CI size (docker --cpus=4, 3 workers: 2044 passed, 25.5 minutes). The npm download cache removed the npm ci stall: 0 to 2 s in every job of run 39722172529, against about 300 s in most jobs before. The workflow's timing comment now records that run; the whole workflow took 8m54s against about 33 minutes before sharding. Shard imbalance (shard 1 carries the concept-comparison specs) is documented, not tuned.	2026-10-21 21:55:21 -07:00
Vito Sansevero	b665aa687d	test(browser): wait for rendering frames, not timers or luck, under load Two Library workflows failed in CI's webkit shard 2/2 (run 39714840809) under parallel load: - "library infinite loading ..." counted cards right after the last page hid "Load more". That render queues the window update for the next frame, so a slow frame left the 120 cards of the all-rows layout in place (received 120, expected < 80). It now waits for the next frame, which runs after every callback the page queued. - "row measurement preserves anchor ..." settled with a 60 ms timer. A scroll event is delivered in a rendering frame, so on a starved renderer the timer ended before the scroll's frame and no card was in view (null anchor). settleLibrary now waits for two consecutive native frames with no Library frame queued, checked inside the frame callback. Before/after: a scratch copy that delays every frame by 120 ms (as a starved runner) failed the old helpers 19 of 40 runs, at the CI lines, and passed the new ones 40 of 40 on chromium and webkit. Throttled to 1 CPU with 4 workers, the original spec failed 1 of 42 for each test. The Tags viewer workflow closed the viewer as soon as its image was visible, before ViewerJS rendered the title, so CI's coverage never ran the page's title callback (tags-page.js functions 26/46 = 56.52%, one function above the floor of 56; locally 27/46). The test now asserts the title names the shown file, which always runs the callback.	2026-10-21 21:22:52 -07:00
Vito Sansevero	f85b45d9a8	ci(viewerjs): cache npm downloads and size timeouts from the first sharded run The first sharded run lost a webkit shard to its 12-minute limit after all 267 tests passed, and npm ci stalled for 5 minutes in six of eight jobs. Each npm ci now restores npm's download cache keyed on the vendor lockfile, and browser job timeouts are the measured times plus at least 50%, never under 20 minutes. The workflow comment records the measurements.	2026-10-21 20:03:13 -07:00
Vito Sansevero	21a2cc0932	ci(viewerjs): run browser suites with workers and shards Frontend coverage runs as three shards (PM_TEST_WORKERS=3 each) that upload their raw V8 files as coverage-raw-N; a merge job downloads them, fails unless all three arrived with raw files and no clashing names, then runs coverage:merge. Firefox and WebKit page workflows run as two shards each with three workers. The required viewerjs context keeps its name and now needs the shards, the merge and the browser shards, failing unless every one succeeded.	2026-10-21 19:41:54 -07:00
Vito Sansevero	3ebf5c48cf	ci(coverage): shard and merge modes for the frontend coverage run frontend-coverage.mjs now plans its steps from the command line. No arguments still runs everything, then reports and checks. --shard I/N runs one slice of the chromium+touch workflows into coverage/js/raw without wiping it or reporting; shard 1 also runs the node units and the viewer suite. --merge-only reports and checks over raw coverage the shards wrote, with --update-baseline as before, and refuses an empty or missing raw dir. npm scripts: test:coverage:shard and coverage:merge.	2026-10-21 19:34:08 -07:00
Vito Sansevero	0156d3fadb	test(browser): test servers bind an OS-chosen port themselves tests/browser/server.py accepts --port 0: it binds 127.0.0.1:0 before building the app, holds that socket for its whole life and prints PM_TEST_SERVER_PORT=<n> to stdout. startBrowserServer defaults to port 0 and reads the announced port, so no port is reserved and released before the server binds and two launchers can no longer race for one. The "address already in use" retry and free-port.mjs are gone; --port N still works and is checked against the announcement.	2026-10-21 18:53:35 -07:00
Vito Sansevero	357c0f09e7	test(browser): one test server per Playwright worker The page workflows started one global webServer and ran with one worker. Each worker now owns its own tests/browser/server.py on an OS-chosen port, with its own temp root and database, through a shared `test` in tests/browser/fixtures.mjs. baseURL, and so page, request and browser.newContext, point at that worker's server. A server that dies fails the running test with its stderr tail and the next test gets a fresh one. The worker count comes from PM_TEST_WORKERS, else 1 under CI, else a quarter of the CPUs up to 8. Chromium workflows in the pinned image: 510 tests in 606 s with one worker on main, 511 (one new isolation spec) in 119 s with eight.	2026-10-21 18:30:22 -07:00