test: use subprocesses for each test file (#29016)

* ci(tests): install ripgrep from prebuilt tarball instead of apt

apt-get update + install of ripgrep takes ~4 min on the GHA Ubuntu
runners (the apt-get update against archive.ubuntu.com is the slow
part; ripgrep itself is small). Switching to the upstream musl
binary tarball cuts the step to a few seconds.

- Pinned to ripgrep 15.1.0 with sha256 verification (same hash as
  published in the releases sha256 sidecar file).
- Drops the `rg` binary into /usr/local/bin so it is on PATH for
  every subsequent step without GITHUB_PATH manipulation.
- Applied to both the test and e2e jobs in tests.yml.

* fix(cli): compile syntax check to tempdir, not source __pycache__

`_validate_critical_files_syntax` runs `py_compile.compile()` on each
critical bootstrap file after a successful `git pull`. The default
`py_compile` writes the resulting `.pyc` next to the source under
`__pycache__/`, which causes two real problems:

1. Parallel test workers walking the same source tree (e.g. running
   the suite under per-file process isolation) can race against each
   other on the `__pycache__` write — manifests as flaky 'directory
   not empty' errors during teardown.
2. In production, the post-pull syntax check leaves a `.pyc` behind
   that the next interpreter run might pick up — fine when the
   interpreter version matches, sketchy if it doesn't.

Fix: write the compiled output to a `tempfile.TemporaryDirectory()`
that's discarded on function exit. We only care about the compile-or-not
signal, not the artifact.

* test(runner): per-file process isolation, drop manual state reset + xdist

Replace fragile manual _reset_module_state test fixtures with robust
per-file subprocess isolation. Each test file runs in a fresh
`python -m pytest <file>` subprocess via ThreadPoolExecutor. No xdist,
no custom pytest plugin, no shared worker state.

Key changes:
  * scripts/run_tests_parallel.py — new runner: discovers test files,
    runs N in parallel via ThreadPoolExecutor, captures stdout per file,
    treats exit code 5 (no tests collected) as pass, kills all children
    on exit. Change from cpu_count to cpu_count*2. The runner is
    I/O-bound (waiting on subprocess.communicate() from pytest children)
    The parent process does almost no CPU work, so 2x oversubscription
    keeps more pipes full. When a file fails, immediately show the last
    30 lines of pytest output (stack traces + FAILED summary) plus a
    ready-to-copy repro command:
      python -m pytest tests/agent/test_auxiliary_client.py
  * scripts/run_tests.sh — delegates to run_tests_parallel.py
  * .github/workflows/tests.yml — test step: python
scripts/run_tests_parallel.py
  * pyproject.toml — drop pytest-xdist, pytest-split; simplify addopts
  * tests/conftest.py — remove ~200 lines of manual state-reset fixtures
  * AGENTS.md — update Testing section for per-file design

* test(runner): speed gateway test antipattern scan up

* fix(test): web search provider plugin test missing xai

* fix(tests): make 14 test files pass under per-file subprocess isolation

Tests that relied on cross-file state pollution from xdist workers
fail when run in isolation (per-file subprocess model). Root causes
and fixes:

Tool registry not populated:
  - test_video_generation_tool_surface_matrix: add discover_builtin_tools()
  - test_web_providers_brave_free/ddgs/searxng/general: autouse fixtures
    registering all 8 bundled web providers, reset after each test
  - test_website_policy: same provider registration pattern
  - test_web_tools_tavily: same pattern across 3 dispatch test classes
  - Also add is_safe_url/check_website_access mocks where SSRF check
    blocks example.com (DNS resolution fails in isolated envs)

Stale check_fn cache:
  - test_kanban_tools: invalidate_check_fn_cache() + _clear_tool_defs_cache()
    in both kanban guidance tests (prior test cached False for kanban_show)
  - test_discord_tool: cache invalidation in setup/teardown
  - test_homeassistant_tool: invalidate_check_fn_cache() before registry queries

Module-level state pollution:
  - test_auxiliary_client: autouse fixture clearing _aux_unhealthy_until cache
  - test_skill_commands: set_session_vars() instead of patch.dict(os.environ)
    (ContextVar takes precedence over os.environ)
  - test_dm_topics: overwrite sys.modules + separate telegram.constants mock
    + force-reimport of gateway.platforms.telegram
  - test_terminal_tool_requirements: removed duplicate class declaration,
    autouse _clear_caches fixture

* change(tests): run_tests.sh explicitly includes env vars

instead of manually dropping some vars, now we just only include some

* fix(tests): 5 more isolation/NixOS fixes

- test_approval_plugin_hooks: isolate HERMES_HOME so real user's
  command_allowlist doesn't short-circuit the approval path
- test_google_chat: skipif when Platform.GOOGLE_CHAT not in enum
  (feature not merged on this branch)
- test_write_deny: test systemd prefix against tmp_path instead of
  /etc/systemd which resolves to /nix/store on NixOS
- test_pty_bridge: use shutil.which('cat') instead of /bin/cat
  (doesn't exist on NixOS)
- profiles.py: rmtree onexc handler chmod's parent dirs too, fixing
  profile deletion when copytree preserved read-only modes from
  nix store

* fix(tests): clear unhealthy cache in autouse fixture for auxiliary_client

* fix(tests): skip send_message when telegram not installed; handle missing worker_id in browser_supervisor

* fix: py3.11 rmtree onexc compat + belt-and-suspenders unhealthy cache clear for expired codex test

* fix: address PR #29016 review feedback

- Remove tracked .pytest-cache/ artifact and add to .gitignore
- Fix stale 'xdist worker' comment in conftest.py
- Deduplicate web provider registration into tests/tools/conftest.py
  shared helper (register_all_web_providers), replacing 8 copy-pasted
  blocks across 6 test files
- Update PR description: remove stale recovered-test-files claim,
  fix worker count to match code (cpu_count*2)

* fix: eliminate race in stale-cache achievements test

The background scan thread could complete and overwrite _SNAPSHOT_CACHE
before evaluate_all() returned the stale data — only 10 fake sessions
made the scan finish instantly. Added scan_delay param to _FakeSessionDB
and set it to 2s in the stale-cache test so the background thread can't
win the race.

tests/gateway/conftest.py

@@ -313,19 +313,30 @@ def _scan_for_plugin_adapter_antipattern(source: str) -> list[str]:
     return offenses
 
 
-def pytest_configure(config):
-    """Reject plugin-adapter tests that use the sys.path anti-pattern.
+def _fingerprint_gateway_tests() -> str:
+    """Return a short fingerprint that changes when any gateway test file changes.
 
-    Runs once per pytest session on the controller, BEFORE any xdist
-    worker is spawned. If any file under ``tests/gateway/`` matches the
-    anti-pattern, we fail the whole session with a clear message —
-    before a polluted ``sys.path`` can cascade across workers.
+    Uses (mtime, size) pairs instead of content hashing — fast to compute
+    (stat-only, no reads) and sufficient for cache invalidation across
+    per-file subprocess runs.
     """
-    # Only run on the xdist controller (or in non-xdist runs). Skip on
-    # worker subprocesses so we don't scan the filesystem N times.
-    if hasattr(config, "workerinput"):
-        return
+    import hashlib
 
+    h = hashlib.sha256()
+    for path in sorted(_GATEWAY_DIR.rglob("test_*.py")):
+        try:
+            st = path.stat()
+            h.update(f"{path.name}:{st.st_mtime_ns}:{st.st_size}".encode())
+        except OSError:
+            h.update(f"{path.name}:missing".encode())
+    return h.hexdigest()[:16]
+
+
+def _run_adapter_antipattern_scan() -> list[str]:
+    """Scan gateway test files for the plugin-adapter anti-pattern.
+
+    Returns a list of violation strings (empty if clean).
+    """
     violations: list[str] = []
     for path in _GATEWAY_DIR.rglob("test_*.py"):
         if path.name in {"_plugin_adapter_loader.py", "conftest.py"}:
@@ -334,20 +345,108 @@ def pytest_configure(config):
             source = path.read_text(encoding="utf-8")
         except OSError:
             continue
+        # Fast string pre-filter: skip files that can't possibly violate.
+        # A violating file MUST contain both (a) an adapter/plugins/platforms
+        # reference AND (b) either sys.path manipulation or a bare adapter import.
         if "adapter" not in source and "plugins/platforms" not in source:
             continue
+        if not (
+            "sys.path" in source
+            or "import adapter" in source
+            or "from adapter import" in source
+        ):
+            continue
         offenses = _scan_for_plugin_adapter_antipattern(source)
         if offenses:
             violations.append(
                 f"  {path.relative_to(_GATEWAY_DIR.parent.parent)}:\n    "
                 + "\n    ".join(offenses)
             )
+    return violations
 
-    if violations:
-        raise pytest.UsageError(
-            "Plugin-adapter-import anti-pattern detected in gateway tests:\n"
-            + "\n".join(violations)
-            + "\n\n"
-            + _GUARD_HINT
-        )
+
+def pytest_configure(config):
+    """Reject plugin-adapter tests that use the sys.path anti-pattern.
+
+    Runs once per pytest session on the controller, BEFORE any xdist
+    worker is spawned. If any file under ``tests/gateway/`` matches the
+    anti-pattern, we fail the whole session with a clear message —
+    before a polluted ``sys.path`` can cascade across workers.
+
+    **Performance**: in the per-file subprocess isolation model (no xdist),
+    every subprocess is a "controller" — so the naive scan would run 257
+    times, each costing ~1s of AST walking.  We avoid this with two
+    strategies:
+
+    1. **Tight string pre-filter**: a file can only violate if it contains
+       *both* an adapter/plugins/platforms reference *and* a sys.path
+       manipulation or bare ``import adapter``.  This drops ~95% of files
+       from needing AST parsing.
+    2. **File-locked cache**: the scan result is cached in
+       ``.pytest-cache/gw-adapter-guard-<fingerprint>`` keyed on a
+       fingerprint of the gateway test file mtimes/sizes.  Concurrent
+       subprocesses acquire a lock; only the first performs the scan;
+       the rest wait and read the cached result.
+    """
+    # Only run on the xdist controller (or in non-xdist runs). Skip on
+    # worker subprocesses so we don't scan the filesystem N times.
+    if hasattr(config, "workerinput"):
+        return
+
+    fp = _fingerprint_gateway_tests()
+    cache_dir = Path.cwd() / ".pytest-cache"
+    cache_file = cache_dir / f"gw-adapter-guard-{fp}"
+    lock_file = cache_dir / f".gw-adapter-guard-{fp}.lock"
+
+    cache_dir.mkdir(parents=True, exist_ok=True)
+
+    # Evict stale cache entries from previous fingerprints (best-effort).
+    try:
+        for old in cache_dir.glob("gw-adapter-guard-*"):
+            if old.name != f"gw-adapter-guard-{fp}":
+                old.unlink(missing_ok=True)
+        for old in cache_dir.glob(".gw-adapter-guard-*.lock"):
+            if old.name != f".gw-adapter-guard-{fp}.lock":
+                old.unlink(missing_ok=True)
+    except OSError:
+        pass  # Non-critical; old files are harmless.
+
+    # Use filelock to ensure only one process scans at a time.
+    # Concurrent subprocesses all hit pytest_configure simultaneously;
+    # without a lock they'd all find no cache and all run the scan.
+    try:
+        from filelock import FileLock
+        lock = FileLock(str(lock_file), timeout=120)
+    except ImportError:
+        # Fallback: no locking (still correct, just slower under contention).
+        import contextlib
+
+        class _NoLock:
+            def __enter__(self):
+                return self
+            def __exit__(self, *a):
+                pass
+        lock = _NoLock()
+
+    with lock:
+        if cache_file.exists():
+            cached = cache_file.read_text(encoding="utf-8")
+            if cached == "clean":
+                return
+            raise pytest.UsageError(cached)
+
+        # Slow path: this process is the first to acquire the lock.
+        violations = _run_adapter_antipattern_scan()
+
+        if violations:
+            msg = (
+                "Plugin-adapter-import anti-pattern detected in gateway tests:\n"
+                + "\n".join(violations)
+                + "\n\n"
+                + _GUARD_HINT
+            )
+            cache_file.write_text(msg, encoding="utf-8")
+            raise pytest.UsageError(msg)
+        else:
+            cache_file.write_text("clean", encoding="utf-8")