Add regression tests for camoufox server

Cover both failure modes from #656 and pin the driver entrypoint
contract, so a future Playwright reshuffle fails in CI rather than in a
user's terminal. No browser download or launch, so they run anywhere.

Refs #656

pythonlib/tests/test_server.py

@@ -0,0 +1,104 @@
+"""
+Tests for camoufox.server.
+
+Regression cover for #656: `python -m camoufox server` broke on Playwright
+1.60, which bundled away the private `lib/browserServerImpl.js` that
+launchServer.js reached into. The two tests below pin the invariants the fix
+relies on, so the next time Playwright reshuffles its internals this fails in
+CI rather than in a user's terminal.
+
+These need Playwright's driver (a dependency) but never download or launch a
+browser, so they stay fast enough to run anywhere.
+
+Run with:
+    cd pythonlib && python -m pytest tests/test_server.py -v
+"""
+
+import base64
+import os
+import subprocess
+import sys
+from pathlib import Path
+
+import orjson
+import pytest
+
+# Make `import camoufox` resolve to the in-tree pythonlib without an install.
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), ".."))
+
+from camoufox import server  # noqa: E402
+from camoufox.server import get_nodejs  # noqa: E402
+
+# Anything on the driver's private lib/ path is fair game for Playwright to
+# move between releases; only the package entrypoint is a supported contract.
+MODULE_ERRORS = ("Cannot find module", "MODULE_NOT_FOUND")
+
+
+def _driver_package() -> Path:
+    return Path(get_nodejs()).parent / "package"
+
+
+def test_driver_entrypoint_exposes_launch_server():
+    # launchServer.js calls playwright.firefox.launchServer() through the
+    # driver's entrypoint. The driver is a bundled copy of playwright-core, so
+    # this is public API -- but assert it rather than assume it, since the whole
+    # bug was an assumption about driver layout going stale.
+    nodejs = get_nodejs()
+    result = subprocess.run(
+        [
+            nodejs,
+            "-e",
+            "const pw = require(process.argv[1]);"
+            "console.log(typeof pw.firefox.launchServer)",
+            str(_driver_package() / "index.js"),
+        ],
+        capture_output=True,
+        text=True,
+        timeout=60,
+    )
+    assert result.returncode == 0, result.stderr
+    assert result.stdout.strip() == "function", result.stdout
+
+
+def test_launch_script_resolves_driver_against_installed_playwright():
+    # The #656 symptom exactly: launchServer.js died at require() time with
+    # MODULE_NOT_FOUND before it ever read its config. Drive the real script
+    # with a config pointing at a binary that does not exist -- reaching a
+    # browser-launch failure proves require() and config parsing both worked.
+    nodejs = get_nodejs()
+    package = _driver_package()
+    result = subprocess.run(
+        [nodejs, str(server.LAUNCH_SCRIPT), str(package)],
+        input=base64.b64encode(
+            orjson.dumps({"executablePath": "/nonexistent/camoufox-bin"})
+        ).decode(),
+        capture_output=True,
+        text=True,
+        timeout=120,
+    )
+    combined = result.stdout + result.stderr
+    for error in MODULE_ERRORS:
+        assert error not in combined, f"driver failed to resolve:\n{combined}"
+    assert "Launching server..." in combined, combined
+    assert "executable doesn't exist" in combined, combined
+
+
+def test_launch_server_surfaces_child_exit_instead_of_pipe_error(monkeypatch, tmp_path):
+    # The traceback in #656 was masked twice over: node died, then writing the
+    # config to its dead stdin raised BrokenPipeError (EINVAL on Windows),
+    # burying the real cause. launch_server() must report the child's exit.
+    script = tmp_path / "dies_immediately.js"
+    script.write_text("process.exit(3);\n")
+
+    # Oversized so the write cannot fit in the pipe buffer and must hit the
+    # closed pipe -- otherwise a small config lands in the buffer and the
+    # regression stays invisible.
+    monkeypatch.setattr(
+        server, "launch_options", lambda **kwargs: {"pad": "x" * 500_000}
+    )
+    monkeypatch.setattr(server, "LAUNCH_SCRIPT", script)
+
+    with pytest.raises(RuntimeError) as excinfo:
+        server.launch_server()
+
+    assert "3" in str(excinfo.value), str(excinfo.value)