feat(seo-data): CrUX field-data fetch with mock mode and graceful degrade

lib/seo-data/fixtures/crux_mobile.json

@@ -0,0 +1,4 @@
+{"record":{"key":{"formFactor":"PHONE"},"metrics":{
+  "largest_contentful_paint":{"percentiles":{"p75":2100}},
+  "interaction_to_next_paint":{"percentiles":{"p75":180}},
+  "cumulative_layout_shift":{"percentiles":{"p75":"0.08"}}}}}

lib/seo-data/google_seo.py

@@ -0,0 +1,76 @@
+#!/usr/bin/env python3
+"""CrUX + GSC fetch → normalized JSON. Third-party imports are LAZY so mock and
+degraded paths run stdlib-only (no venv, no network)."""
+import argparse, json, os, sys
+
+def _mock(name):
+    d = os.environ.get("SEO_DATA_MOCK_DIR")
+    if not d:
+        return None
+    path = os.path.join(d, name)
+    if not os.path.exists(path):
+        return None
+    with open(path, encoding="utf-8") as f:
+        return json.load(f)
+
+def _norm_crux(raw):
+    m = raw["record"]["metrics"]
+    def p75(metric):
+        return m.get(metric, {}).get("percentiles", {}).get("p75")
+    out = {"status": "ok", "source": "crux"}
+    lcp = p75("largest_contentful_paint")
+    inp = p75("interaction_to_next_paint")
+    cls = p75("cumulative_layout_shift")
+    # Low-traffic origins often miss a metric (INP notably) — omit, don't crash.
+    if lcp is not None:
+        out["lcp_p75_ms"] = int(lcp)
+    if inp is not None:
+        out["inp_p75_ms"] = int(inp)
+    if cls is not None:
+        out["cls_p75"] = float(cls)
+    if len(out) == 2:  # no metric at all
+        return {"status": "degraded", "reason": "no_field_data"}
+    return out
+
+def _crux_query(key, body):
+    import requests  # lazy
+    return requests.post(
+        "https://chromeuxreport.googleapis.com/v1/records:queryRecord?key=" + key,
+        json=body, timeout=20)
+
+def crux(url, strategy="mobile"):
+    raw = _mock("crux_%s.json" % strategy)
+    if raw is None:
+        key = os.environ.get("CRUX_API_KEY")
+        if not key:
+            return {"status": "degraded", "reason": "no_crux_key"}
+        ff = "PHONE" if strategy == "mobile" else "DESKTOP"
+        r = _crux_query(key, {"url": url, "formFactor": ff})
+        if r.status_code == 404:  # no page-level data → try origin-level
+            r = _crux_query(key, {"origin": url.rstrip("/"), "formFactor": ff})
+        if r.status_code == 404:
+            return {"status": "degraded", "reason": "no_field_data"}
+        if r.status_code == 429:
+            return {"status": "degraded", "reason": "rate_limited"}
+        r.raise_for_status()
+        raw = r.json()
+    return _norm_crux(raw)
+
+def _cli():
+    p = argparse.ArgumentParser()
+    sub = p.add_subparsers(dest="cmd", required=True)
+    pc = sub.add_parser("crux")
+    pc.add_argument("--url", required=True)
+    pc.add_argument("--strategy", default="mobile", choices=["mobile", "desktop"])
+    pc.add_argument("--store", default=None)  # accepted+ignored: uniform fetch.sh dispatch
+    args = p.parse_args()
+    try:
+        if args.cmd == "crux":
+            print(json.dumps(crux(args.url, args.strategy), indent=2))
+    except Exception:
+        # Fail-open data contract: ANY unexpected error (HTTP 403/5xx, DNS,
+        # timeout) degrades with exit 0 — never a traceback, never empty stdout.
+        print(json.dumps({"status": "degraded", "reason": "unexpected_error"}))
+
+if __name__ == "__main__":
+    _cli()

lib/seo-data/seo-data.test.sh

@@ -29,6 +29,18 @@ DPERM="$(stat -c '%a' "$(dirname "$STORE")")"
 [ "$DPERM" = "700" ] && ok "store dir is 0700" || no "store dir 0700" "got $DPERM"
 rm -rf "$TMP"
 
+echo "── crux (mock) ──"
+CRUX_OK="$(SEO_DATA_MOCK_DIR="$REPO/lib/seo-data/fixtures" \
+  python3 "$SD/google_seo.py" crux --url https://ex.com --strategy mobile)"
+has "crux status ok"        "$CRUX_OK" '"status": "ok"'
+has "crux lcp p75 mapped"   "$CRUX_OK" '"lcp_p75_ms": 2100'
+has "crux inp p75 mapped"   "$CRUX_OK" '"inp_p75_ms": 180'
+has "crux cls p75 mapped"   "$CRUX_OK" '"cls_p75": 0.08'
+CRUX_DEG="$(env -u CRUX_API_KEY -u SEO_DATA_MOCK_DIR \
+  python3 "$SD/google_seo.py" crux --url https://ex.com)"
+has "crux degrades w/o key" "$CRUX_DEG" '"status": "degraded"'
+has "crux degrade reason"   "$CRUX_DEG" 'no_crux_key'
+
 echo ""
 echo "seo-data engine: $PASS pass, $FAIL fail"
 [ "$FAIL" -eq 0 ]