feat(shot): mattermost-lts SCREENSHOT hook → /login (default lands the desktop-or-browser interstitial; watch-list wants the real sign-in form) + public screenshot.settle() for hooks; unit test via real loader; 206 unit tests pass, lint PASS

tests/unit/test_screenshot.py

@@ -116,6 +116,33 @@ def test_wait_budget_within_step_cap():
     assert total_ms <= 60_000, f"screenshot wait budget {total_ms}ms exceeds the ~60s step cap"
 
 
+def test_mattermost_screenshot_hook_lands_login():
+    """phase-shot: mattermost-lts ships the first real SCREENSHOT hook — `/` serves the
+    desktop-or-browser interstitial, so the hook must navigate to /login (the representative,
+    credential-free sign-in form) and settle; the harness then snaps the PNG."""
+
+    class _Resp:
+        status = 200
+
+    class _NavPage(_FakePage):
+        def __init__(self):
+            super().__init__([])
+            self.urls = []
+
+        def goto(self, url, wait_until=None, timeout=None):
+            self.urls.append(url)
+            return _Resp()
+
+    tests_dir = os.path.join(os.path.dirname(__file__), "..")
+    meta = meta_mod.load("mattermost-lts", tests_dir=tests_dir)
+    hook = S._load_screenshot_hook(meta)
+    assert callable(hook), "mattermost-lts SCREENSHOT hook missing from the real load path"
+    page = _NavPage()
+    hook(page, meta_mod.hook_ctx("mm.example.org", meta))
+    assert page.urls == ["https://mm.example.org/login"]
+    assert page.idle_waits, "hook must settle before the harness snaps"
+
+
 def test_screenshot_reachable_through_real_load_path(tmp_path):
     """R2 proof (rcust P1): a recipe SCREENSHOT hook declared in recipe_meta.py arrives at
     screenshot._load_screenshot_hook through the REAL orchestrator load path (meta.load — the