feat(python): warn when a supplied binary predates the Playwright in use

A managed install below the version floor is upgraded by pkgman, but
executable_path deliberately bypasses that -- the caller supplied the binary,
so we neither replace it nor download another. That left one pairing nothing
checked: an old build driven by Playwright >= 1.61, which sends viewport fields
the older Juggler schema rejects. The user saw a bare

    Protocol error (Browser.setDefaultViewport)

with nothing naming the cause.

Warn rather than raise, because the pairing is not always fatal. Camoufox
defaults to no_viewport when it spoofs window dimensions (sync_api), and
Playwright then never sends Browser.setDefaultViewport -- so the default path
works fine on an old build. Measured against a real beta.29 binary on
Playwright 1.62:

    default path                     WORKS
    new_context(viewport=...)        BREAKS
    new_context(no_viewport=False)   BREAKS
    new_context(viewport=..., is_mobile=False)  BREAKS

Refusing to launch would break the setups in the first row. A build with no
version.json beside it -- an unpackaged objdir build -- tells us nothing, so it
is left alone rather than nagged about.

Verified end to end: warns on the real beta.29 build under Playwright 1.62,
silent on beta.30.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

pythonlib/tests/test_executable_path_version_warning.py

@@ -0,0 +1,69 @@
+"""A caller's own binary is never replaced -- but it should still be checked.
+
+A managed install below the floor gets upgraded by pkgman. `executable_path`
+deliberately bypasses that, which leaves one pairing nothing checks: an old
+build driven by Playwright >= 1.61, whose viewport fields the older Juggler
+schema rejects. Without this the user sees a bare "Protocol error
+(Browser.setDefaultViewport)" and nothing naming the cause.
+
+It warns rather than raises on purpose: camoufox defaults to no_viewport when
+it spoofs window dimensions, so the default path works on an old build. Only an
+explicit viewport breaks, so refusing to launch would break working setups.
+"""
+
+import json
+
+import pytest
+
+from camoufox import pkgman, utils
+
+
+def _bundle(tmp_path, build):
+    """A browser directory with version.json beside the binary, as a release has."""
+    d = tmp_path / f"152.0.4-{build}"
+    d.mkdir()
+    (d / "version.json").write_text(json.dumps({"version": "152.0.4", "build": build}))
+    return d / "camoufox-bin"
+
+
+@pytest.fixture
+def floor_at_beta30(monkeypatch):
+    monkeypatch.setattr(utils, "effective_version_min", lambda: pkgman.Version(build="beta.30"))
+
+
+def test_warns_when_the_supplied_build_is_too_old(tmp_path, floor_at_beta30):
+    exe = _bundle(tmp_path, "beta.29")
+
+    with pytest.warns(RuntimeWarning, match=r"beta\.29.*beta\.30"):
+        utils.warn_if_executable_predates_playwright(exe)
+
+
+def test_names_the_symptom_the_user_will_actually_see(tmp_path, floor_at_beta30):
+    exe = _bundle(tmp_path, "beta.29")
+
+    with pytest.warns(RuntimeWarning) as caught:
+        utils.warn_if_executable_predates_playwright(exe)
+
+    assert "Browser.setDefaultViewport" in str(caught[0].message)
+
+
+@pytest.mark.parametrize("build", ["beta.30", "beta.31"])
+def test_silent_when_the_build_is_new_enough(tmp_path, floor_at_beta30, build, recwarn):
+    utils.warn_if_executable_predates_playwright(_bundle(tmp_path, build))
+
+    assert not [w for w in recwarn if issubclass(w.category, RuntimeWarning)]
+
+
+def test_silent_for_a_custom_build_with_no_version_json(tmp_path, floor_at_beta30, recwarn):
+    """An unpackaged objdir build tells us nothing; do not nag about it."""
+    (tmp_path / "dist").mkdir()
+
+    utils.warn_if_executable_predates_playwright(tmp_path / "dist" / "camoufox-bin")
+
+    assert not [w for w in recwarn if issubclass(w.category, RuntimeWarning)]
+
+
+def test_silent_when_no_executable_path_was_given(floor_at_beta30, recwarn):
+    utils.warn_if_executable_predates_playwright(None)
+
+    assert not [w for w in recwarn if issubclass(w.category, RuntimeWarning)]