Harden the DDG collector with token-bucket pacing and prefer the ddgs package

docs/asset-tooling.md

@@ -229,7 +229,12 @@ python3 tools/refcollect.py sheet --slug comedy-store   # local contact sheet (n
 ```
 
 Requires `pip install duckduckgo-search` (renamed `ddgs` upstream). DuckDuckGo rate-limits by IP
-(HTTP 202) and the tool retries with backoff, so run per-venue batches spaced out.
+(HTTP 202), so every request — the search itself and each image download — passes through a shared
+token bucket (`--rate`, default 0.5 req/s, and `--burst`, default 3) and a polite retry routine:
+transient statuses (408/425/429/5xx/52x) and network errors back off exponentially with full
+jitter, `Retry-After` is honoured, permanent failures fail fast, and the loop gives up after six
+attempts. Requests carry a full, coherent Firefox header set (`--user-agent` overrides the UA
+string); the UA alone is no longer enough to look like a browser.
 
 ### Reference-board research (`refboard`)