web search via exa (spec-015): web_search tool, sanitized results, per-user cap, host-config key

DECISIONS.md

@@ -60,6 +60,15 @@ Decisions inside the set architecture. D-NNN, never renumbered.
   broken classifier must never mute the bot; the budget gate already
   bounds spend. Its verdict gates BEFORE the main call, the
   envelope's answer_needed still gates after — two independent nets.
+- **D-020** — Web search via Exa (FDB-022, SPEC-015): a `web_search`
+  tool alongside fetch_url/IGDB/codex/get_news, filling the "look it up
+  on the open web" gap. Exa (not a raw search-engine scrape) because it
+  returns clean title+url+text in one call — no SSRF surface of our own
+  (we call one fixed API endpoint, not arbitrary hosts), and it pairs
+  with fetch_url for the full article. Key is a host secret
+  (`exa-api-key`, env `EXA_API_KEY` fallback), never repo-side; results
+  sanitized like every other external-text tool; off by default
+  (`enable-web-search`), metered per user.
 - **D-019** — News memory + on-demand tool (SPEC-013 NEWS-07..12):
   the news pipeline now carries item summaries (feed descriptions,
   HTML-stripped) and persists every fetched item into a deduped `news`