docs: extend the freshness contract to smokes

The contract named benchmark and golden tooling, which is exactly why the smoke
launcher was allowed to skip the check for so long. It now covers every browser
check, names where each one gets it, and records why a stale bundle is worse
than a plain failure: part of the assertions go red and part stay green.

Issue: #236
User-Visible: no

AGENTS.md

@@ -358,9 +358,13 @@ complete Linux CI artifact; never accept a partial scenario or images merely to
 CI green. See `demo/golden/README.md`.
 
 **Freshness contract**: the embedded fingerprint covers `src/` plus Rollup,
-TypeScript and package-lock build inputs. Benchmark and golden tooling must call
-`assertFreshDemoBundle` before recording any result; a missing or mismatched
-fingerprint is a hard failure, not a warning.
+TypeScript and package-lock build inputs. Every browser check must verify it
+before trusting a result — benchmarks, golden runs and documentation captures
+call `assertFreshDemoBundle` themselves, and smokes get it from `launch()` in
+`demo/serve.mjs` (#236). A missing or mismatched fingerprint is a hard failure,
+not a warning; `HP_ALLOW_STALE_BUNDLE=1` skips the check for debugging and says
+so out loud. A smoke against a stale bundle does not fail cleanly: part of its
+assertions go red and part stay green, which reads as a logic defect.
 
 **CI is pinned to an exact SHA.** The release gate accepts only a `completed
 success` run for the candidate's SHA, not "the last green one"; a new push cancels