test/browser: headless-browser smoke client (phase 2)

[kixelated]

Summary

Phase 2 of the cross-language smoke test (#1529 was phase 1). Adds a headless-browser client so the smoke test covers the independent JS/WebCodecs implementation interoperating with the native Rust/Python clients over WebTransport.

The full rust × python × js-browser matrix passes in every direction:

rust       → rust ✓   python ✓   js-browser ✓
python     → rust ✓   python ✓   js-browser ✓
js-browser → rust ✓   python ✓   js-browser ✓

How the browser client works

• nix-provisioned Chromium: flake.nix pulls playwright-driver.browsers and sets PLAYWRIGHT_BROWSERS_PATH (npm playwright pinned to the driver's 1.58.2) — no Playwright browser download, reproducible.
• test/browser/: a standalone Vite page using the real <moq-publish> / <moq-watch> elements, driven by a Playwright runner (driver.ts):
  • Launches full Chromium with channel: "chromium" (the new headless mode — the default chrome-headless-shell lacks WebTransport/WebCodecs/mediaDevices).
  • publish: a fake camera (--use-fake-device-for-media-stream) → WebCodecs H.264 encode → streams until killed.
  • subscribe: exits 0 once <moq-watch>'s stats signal reports a decoded frame.
  • Served as a prebuilt static bundle (not a live Vite server) to avoid concurrent dep-optimizer deadlocks.

Things that needed solving (documented in code)

• <moq-watch> only subscribes to/decodes video when it has a render target, and @moq/publish encodes lazily on demand — so the subscriber page adds a <canvas>.
• smoke.py now waits for a catalog update that carries a video track (the browser publisher announces video in a later catalog, not the first snapshot).
• The browser watch gives up if it subscribes to the catalog before the publisher announces it (RESET_STREAM), so test/smoke.sh adds a publisher warmup and the driver reloads once mid-timeout to recover from the race.

Defaults & CI

• Default just test smoke stays rust,python (fast; browser cells spin Chromium).
• js-browser is opt-in via --publishers/--subscribers; the nightly smoke.yml runs the full matrix (--timeout 30).

Notes for reviewers

• Validated locally on macOS (full matrix green). The nightly will be the first run on Linux CI Chromium — it's non-blocking (manual + schedule), so any Linux-headless tweaks surface there without gating PRs.
• shfmt / shellcheck / ruff / biome / actionlint / nixfmt all clean.

Test plan

• just test smoke --publishers rust,python,js-browser --subscribers rust,python,js-browser --timeout 30 → all 9 cells PASS
• default just test smoke (rust,python) still green
• nightly smoke.yml on Linux CI

🤖 Generated with Claude Code

(Written by Claude)

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: e96bcbb8-68ab-4c19-9c81-2ac698028ffa

📥 Commits

Reviewing files that changed from the base of the PR and between a881ac3 and 2c69f87.

📒 Files selected for processing (1)

• py/moq-rs/examples/smoke.py

🚧 Files skipped from review as they are similar to previous changes (1)

• py/moq-rs/examples/smoke.py

---

Walkthrough

This PR adds browser-based smoke testing to the MOQ interop test suite. It introduces a new test/browser workspace with a TypeScript test client and Playwright-driven CLI harness, integrates the browser harness into test/smoke.sh (including a WARMUP delay), updates Nix to provide Playwright browser binaries, makes the Python smoke client wait for a catalog with video, and updates CI to include js-browser in the smoke test matrix.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately and specifically describes the main change: adding a headless-browser smoke client for the cross-language test suite.
Description check	✅ Passed	The description is comprehensive and directly related to the changeset, explaining the browser client implementation, matrix testing, nix provisioning, and race condition solutions.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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🧹 Nitpick comments (1)

py/moq-rs/examples/smoke.py (1)

46-53: ⚡ Quick win

Add type hints for consistency with the file's existing style.

All other functions in this file include type hints (publish, subscribe, main), but _catalog_with_video does not. Adding type hints would improve consistency and provide better IDE/tooling support.

♻️ Suggested type hints

-async def _catalog_with_video(consumer):
+async def _catalog_with_video(consumer: moq.BroadcastConsumer) -> moq.Catalog:
     # The catalog is a live track. A lazy publisher (e.g. the browser, which only

Note: Use the appropriate type names from the moq library's interface. If the exact types are not exported, consider using typing.Any or Protocol types as appropriate.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@py/moq-rs/examples/smoke.py` around lines 46 - 53, Add missing type hints to
the _catalog_with_video function: annotate the consumer parameter with the
appropriate type (e.g., moq.Consumer or typing.Any if moq.Consumer/Catalog types
are not exported) and add a return type annotation (e.g., -> moq.Catalog or ->
typing.Any). Update the signature of _catalog_with_video to include these
annotations so it matches the other functions (publish, subscribe, main) in the
file and improves IDE/tooling support.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@py/moq-rs/examples/smoke.py`:
- Around line 46-53: Add missing type hints to the _catalog_with_video function:
annotate the consumer parameter with the appropriate type (e.g., moq.Consumer or
typing.Any if moq.Consumer/Catalog types are not exported) and add a return type
annotation (e.g., -> moq.Catalog or -> typing.Any). Update the signature of
_catalog_with_video to include these annotations so it matches the other
functions (publish, subscribe, main) in the file and improves IDE/tooling
support.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: b9444f51-8dcb-476c-b2dc-747b65c5993f

📥 Commits

Reviewing files that changed from the base of the PR and between ab08b0c and a881ac3.

⛔ Files ignored due to path filters (1)

• bun.lock is excluded by !**/*.lock

📒 Files selected for processing (10)

• .github/workflows/smoke.yml
• flake.nix
• package.json
• py/moq-rs/examples/smoke.py
• test/browser/driver.ts
• test/browser/index.html
• test/browser/package.json
• test/browser/src/main.ts
• test/browser/vite.config.ts
• test/smoke.sh