build(ci): harden preview perf gate startup

code/scripts/preview_perf_benchmark.py

@@ -38,14 +38,24 @@ def _fetch_json(url: str) -> Dict[str, Any]:
 
 
 def _fetch_json_with_retry(url: str, attempts: int = 3, delay: float = 0.6) -> Dict[str, Any]:
+    last_error: Exception | None = None
     for attempt in range(1, attempts + 1):
         try:
             return _fetch_json(url)
-        except Exception:  # pragma: no cover - network variability
+        except Exception as exc:  # pragma: no cover - network variability
+            last_error = exc
             if attempt < attempts:
+                print(json.dumps({  # noqa: T201
+                    "event": "preview_perf_fetch_retry",
+                    "url": url,
+                    "attempt": attempt,
+                    "max_attempts": attempts,
+                    "error": str(exc),
+                }))
                 time.sleep(delay * attempt)
             else:
                 raise
+    raise last_error  # pragma: no cover - defensive; should be unreachable
 
 
 def select_theme_slugs(base_url: str, count: int) -> List[str]:
@@ -97,12 +107,31 @@ def fetch_all_theme_slugs(base_url: str, page_limit: int = 200) -> List[str]:
     slugs: List[str] = []
     offset = 0
     seen: set[str] = set()
+    page_attempts = 5
+    page_delay = 1.2
     while True:
-        try:
-            url = f"{base_url.rstrip('/')}/themes/api/themes?limit={page_limit}&offset={offset}"
-            data = _fetch_json_with_retry(url)
-        except Exception as e:  # pragma: no cover - network variability
-            raise SystemExit(f"Failed fetching themes page offset={offset}: {e}")
+        url = f"{base_url.rstrip('/')}/themes/api/themes?limit={page_limit}&offset={offset}"
+        data: Dict[str, Any] | None = None
+        last_error: Exception | None = None
+        for attempt in range(1, page_attempts + 1):
+            try:
+                data = _fetch_json_with_retry(url, attempts=4, delay=0.75)
+                break
+            except Exception as exc:  # pragma: no cover - network variability
+                last_error = exc
+                if attempt < page_attempts:
+                    print(json.dumps({  # noqa: T201
+                        "event": "preview_perf_page_retry",
+                        "offset": offset,
+                        "attempt": attempt,
+                        "max_attempts": page_attempts,
+                        "error": str(exc),
+                    }))
+                    time.sleep(page_delay * attempt)
+                else:
+                    raise SystemExit(f"Failed fetching themes page offset={offset}: {exc}")
+        if data is None:  # pragma: no cover - defensive
+            raise SystemExit(f"Failed fetching themes page offset={offset}: {last_error}")
         items = data.get("items") or []
         for it in items:
             if not isinstance(it, dict):

code/scripts/preview_perf_ci_check.py

@@ -25,7 +25,7 @@ import time
 import urllib.error
 import urllib.request
 from pathlib import Path
-def _wait_for_service(base_url: str, attempts: int = 8, delay: float = 1.5) -> bool:
+def _wait_for_service(base_url: str, attempts: int = 12, delay: float = 1.5) -> bool:
     health_url = base_url.rstrip("/") + "/healthz"
     last_error: Exception | None = None
     for attempt in range(1, attempts + 1):
@@ -40,7 +40,7 @@ def _wait_for_service(base_url: str, attempts: int = 8, delay: float = 1.5) -> b
                 break
         except Exception as exc:  # pragma: no cover - network variability
             last_error = exc
-        time.sleep(delay)
+    time.sleep(delay * attempt)
     print(json.dumps({
         "event": "ci_perf_error",
         "stage": "startup",

code/tests/test_preview_perf_fetch_retry.py

@@ -18,3 +18,22 @@ def test_fetch_all_theme_slugs_retries(monkeypatch):
 
     assert slugs == ["alpha"]
     assert calls["count"] == 2
+
+
+def test_fetch_all_theme_slugs_page_level_retry(monkeypatch):
+    calls = {"count": 0}
+
+    def fake_fetch_with_retry(url, attempts=3, delay=0.6):  # type: ignore[override]
+        calls["count"] += 1
+        if calls["count"] < 3:
+            raise RuntimeError("service warming up")
+        assert url.endswith("offset=0")
+        return {"items": [{"id": "alpha"}], "next_offset": None}
+
+    monkeypatch.setattr(perf, "_fetch_json_with_retry", fake_fetch_with_retry)
+    monkeypatch.setattr(perf.time, "sleep", lambda *_args, **_kwargs: None)
+
+    slugs = perf.fetch_all_theme_slugs("http://example.com", page_limit=1)
+
+    assert slugs == ["alpha"]
+    assert calls["count"] == 3

code/web/app.py

@@ -105,7 +105,7 @@ SHOW_SETUP = _as_bool(os.getenv("SHOW_SETUP"), True)
 SHOW_DIAGNOSTICS = _as_bool(os.getenv("SHOW_DIAGNOSTICS"), False)
 SHOW_COMMANDERS = _as_bool(os.getenv("SHOW_COMMANDERS"), True)
 SHOW_VIRTUALIZE = _as_bool(os.getenv("WEB_VIRTUALIZE"), False)
-ENABLE_THEMES = _as_bool(os.getenv("ENABLE_THEMES"), False)
+ENABLE_THEMES = _as_bool(os.getenv("ENABLE_THEMES"), True)
 ENABLE_PWA = _as_bool(os.getenv("ENABLE_PWA"), False)
 ENABLE_PRESETS = _as_bool(os.getenv("ENABLE_PRESETS"), False)
 ALLOW_MUST_HAVES = _as_bool(os.getenv("ALLOW_MUST_HAVES"), False)