fix(adapters): shared retry helper + run_log failure_class + enable RSS (issues #1 #2 #9)

- adapters/__init__.py: add http_get() unified retry (429/5xx only, max 2
  attempts, capped exp backoff) + AdapterHTTPError carrying failure_class;
  SourceAdapter.last_failure_class set on failure for pipeline capture.
- arxiv/github/huggingface/hackernews/reddit: route HTTP through http_get.
  Preserves GitHub 403 rate-limit retry and Reddit 403/429 fast-bail.
- schema.sql + pipeline.py: add run_log.failure_class column; rollup most-
  severe class across sources (5xx>4xx>429>error>zero_fetch>ok).
- pipeline.py: ENABLE RSS in ENABLED_SOURCES (was registered, disabled).
- RSS smoke test surfaced 3 broken feeds (anthropic 404, googleai 404,
  metaai 301) — left as-is, captured in feed_failures; URL fix is separate
  discovery task, not guessed.

Verified: full dry-run fetches all 6 sources; github live fetch OK;
Reddit 429 fast-bail preserved; no import/syntax errors.

pipeline.py

@@ -37,7 +37,7 @@ ADAPTERS = {
 }
 
 # Default enabled sources
-ENABLED_SOURCES = ["github", "arxiv", "reddit", "hackernews", "huggingface"]
+ENABLED_SOURCES = ["github", "arxiv", "reddit", "hackernews", "huggingface", "rss"]
 
 
 def init_db(db_path: str, schema_path: str) -> sqlite3.Connection:
@@ -252,9 +252,14 @@ def run_pipeline(sources: list[str] | None = None, limit: int = 20, dry_run: boo
             entries = adapter.fetch(limit=limit)
         except Exception as e:
             print(f"  ✗ {source_name} failed: {e}")
-            source_stats[source_name] = {"fetched": 0, "stored": 0, "error": str(e)}
+            source_stats[source_name] = {"fetched": 0, "stored": 0,
+                                         "error": str(e),
+                                         "failure_class": "error"}
             continue
 
+        # Capture classification from the adapter (set by http_get on failure)
+        fc = getattr(adapter, "last_failure_class", None)
+
         # Add adapter_version to metadata
         for entry in entries:
             meta = json.loads(entry["raw_metadata"]) if isinstance(entry["raw_metadata"], str) else entry["raw_metadata"]
@@ -262,7 +267,8 @@ def run_pipeline(sources: list[str] | None = None, limit: int = 20, dry_run: boo
             entry["raw_metadata"] = json.dumps(meta)
 
         all_entries.extend(entries)
-        source_stats[source_name] = {"fetched": len(entries), "stored": 0}
+        source_stats[source_name] = {"fetched": len(entries), "stored": 0,
+                                     "failure_class": fc or "ok"}
         print(f"    Fetched: {len(entries)} entries")
 
         # Small spacing between sources
@@ -294,16 +300,31 @@ def run_pipeline(sources: list[str] | None = None, limit: int = 20, dry_run: boo
         # Zero-fetch (e.g. Reddit fully rate-limited) raises no exception but
         # is still a degraded run — record it so run_log can tell
         # "intermittent vs consistently-broken" apart over time.
-        zero = [s for s, st in source_stats.items() if st.get("fetched", 0) == 0 and not st.get("error")]
+        zero = [s for s, st in source_stats.items()
+                if st.get("fetched", 0) == 0 and not st.get("error")]
         notes_parts = [f"{s}: {st['error']}" for s, st in source_stats.items() if st.get("error")]
         if zero:
             notes_parts.append(f"no-fetch (degraded): {', '.join(zero)}")
         notes = "; ".join(notes_parts) or "all sources ok"
+
+        # Rollup failure_class (issue #2): most severe across sources.
+        # Priority: 5xx > 4xx > 429 > error > zero_fetch > ok
+        rank = {"5xx": 5, "4xx": 4, "429": 3, "error": 2, "zero_fetch": 1, "ok": 0}
+        classes = [st.get("failure_class", "ok") for st in source_stats.values()]
+        if any(c in ("5xx", "4xx", "429", "error") for c in classes):
+            run_fc = max((c for c in classes if c in rank),
+                         key=lambda c: rank[c])
+        elif zero:
+            run_fc = "zero_fetch"
+        else:
+            run_fc = "ok"
         try:
             conn.execute("""
-                INSERT INTO run_log (total_fetched, total_stored, sources_ok, sources_failed, notes)
-                VALUES (?, ?, ?, ?, ?)
-            """, (len(all_entries), stored, json.dumps(ok), json.dumps(failed), notes))
+                INSERT INTO run_log (total_fetched, total_stored, sources_ok,
+                                     sources_failed, failure_class, notes)
+                VALUES (?, ?, ?, ?, ?, ?)
+            """, (len(all_entries), stored, json.dumps(ok), json.dumps(failed),
+                  run_fc, notes))
             conn.commit()
         except Exception as e:
             print(f"  ⚠ run_log write failed: {e}")