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

runner/harness/screenshot.py

@@ -58,6 +58,12 @@ def _settle(page, idle_timeout_ms: int) -> None:
         page.wait_for_timeout(RENDER_GRACE_MS)
 
 
+def settle(page, idle_timeout_ms: int = SETTLE_TIMEOUT_MS) -> None:
+    """Public settle for recipe SCREENSHOT hooks: after the hook navigates to its safe view, call
+    this so the snap happens post-paint. Same bounded best-effort contract as the default path."""
+    _settle(page, idle_timeout_ms)
+
+
 def _snap_with_blank_retry(page, out_path: str) -> None:
     """Screenshot the page; if the PNG is blank/spinner-sized, retry ONCE after a longer settle.
     The retry overwrites the tiny frame with a strictly-later one (same page, more paint time)."""

tests/mattermost-lts/recipe_meta.py

@@ -18,3 +18,22 @@ HEALTH_OK = (200, 302)
 DEPLOY_TIMEOUT = 900
 HTTP_TIMEOUT = 600
 EXTRA_ENV = {"TIMEOUT": "600"}
+
+
+def SCREENSHOT(page, ctx):
+    """Land the real sign-in form for the CI card (phase-shot). The default landing capture gets
+    mattermost's "view in desktop app or browser?" interstitial at `/` — a real page but not
+    representative of the app. `/login` renders the standard login form directly. Credential-free
+    (empty fields, R7 secret-safety: never a page showing generated secrets); the harness snaps
+    the PNG after this returns."""
+    from harness import browser as harness_browser
+    from harness import screenshot as screenshot_mod
+
+    harness_browser.goto_with_retry(
+        page,
+        f"{ctx.base_url}/login",
+        accept_statuses=(200,),
+        deadline_seconds=screenshot_mod.NAV_DEADLINE_S,
+        wait_until="domcontentloaded",
+    )
+    screenshot_mod.settle(page)

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