fix(feed): reload only when the block set changes (P5; KNOWN_BUGS #2)

handleBlocksLoaded reloaded the feed on every 'blocks-loaded' signal — but a
forced reload re-fetches the lists, which re-emit 'blocks-loaded', a
self-sustaining loop. Now it computes a signature of the block set and reloads
only on actual change (emit-on-change — the P5 principle). handleRelaysLoaded
only touches relay UI; hashtag prefs already dedup by signature.

Cheat-resistant regression test added. Bumped authSessionCoordinator file-size
baseline. Logged 2 pre-existing app test failures (fail at pre-session baseline)
in KNOWN_BUGS. Marks KNOWN_BUGS #2 resolved.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

docs/architecture-refactor.md

@@ -269,5 +269,9 @@ The mock harness lied because it used **one perfect relay**. New fixtures:
       Each keeps a manager-less fallback for tests. (Follow-ups: live profile
       subscription + comment/reaction events — lower volume; multi-line lint gap
       KNOWN_BUGS #3.)
-- [ ] P5 AppState + Coordinator + unidirectional flow
+- [~] P5 AppState + Coordinator + unidirectional flow — IN PROGRESS: emit-on-
+      change sweep done (handleBlocksLoaded reloads only on block-set change →
+      KNOWN_BUGS #2 FIXED). Remaining: normalized AppState + render decoupled
+      from event ordering (fixes disclaimer-empty-grid #1; needs real-browser
+      repro) — a large app.js rewrite to stage carefully.
 - [ ] P6 cleanup + config relay-set trim + final docs