review: gate web Reddit enrichment behind EXCLUDE_SOURCES

PR #366 routes Reddit URLs found in web-search results through the public
Reddit JSON API to recover thread body + top comments (the Claude Code
WebFetch tool blocks reddit.com directly). That bypass is sound and the
fixed problem is real - but the always-on shape ignores user intent on
source gating.

A user who sets EXCLUDE_SOURCES=reddit to suppress Reddit results would
still get Reddit content smuggled back in via web-search URLs that
happen to point at reddit.com threads. This contradicts the suppression
contract that EXCLUDE_SOURCES is supposed to provide (see
lib/pipeline.available_sources where the same env var gates the
top-level Reddit source).

Add a _reddit_excluded(config) check in web_search() that mirrors the
parsing pattern from lib/pipeline (comma-separated, case-insensitive,
whitespace-tolerant). When reddit is in EXCLUDE_SOURCES, skip the
enrichment pass entirely - the web results themselves still flow
through, but they're not augmented with Reddit body/comments.

Four new tests in test_grounding_v3.py cover:
- EXCLUDE_SOURCES=reddit skips enrichment
- case-insensitive parsing matches REDDIT/Reddit/whitespace-padded/csv
- Other sources in EXCLUDE_SOURCES don't trigger the gate
- Enrichment runs normally when reddit isn't excluded

19/19 grounding tests pass.

skills/last30days/scripts/lib/grounding.py

@@ -232,17 +232,32 @@ def web_search(
         raise ValueError(f"Unsupported web backend: {backend!r}")
     else:
         return [], {}
-    if items:
+    if items and not _reddit_excluded(config):
         items = _enrich_reddit_items(items)
     return items, artifact
 
 
+def _reddit_excluded(config: dict) -> bool:
+    """Return True when EXCLUDE_SOURCES contains 'reddit'.
+
+    Respects the same suppression knob the pipeline uses for source gating,
+    so a user who set EXCLUDE_SOURCES=reddit doesn't get Reddit content
+    smuggled back in via web-search URLs.
+    """
+    raw = (config.get("EXCLUDE_SOURCES") or "").split(",")
+    return any(s.strip().lower() == "reddit" for s in raw)
+
+
 def _enrich_reddit_items(items: list[dict]) -> list[dict]:
     """Enrich web search results that are Reddit URLs with thread body and comments.
 
     Claude Code's WebFetch blocks reddit.com, so the model can't retrieve
     Reddit content from web search results. This fetches it via the public
     JSON API (reddit.com/.../.json) which bypasses that restriction.
+
+    Callers should gate this with EXCLUDE_SOURCES=reddit handling (see
+    `_reddit_excluded`) so a user who explicitly excluded Reddit doesn't
+    get Reddit content via web-search URLs.
     """
     from . import reddit_enrich