[viewer][P0] #746 stuck-backstop false-fires on healthy 300–500s turns (cold-open budget band)

[100yenadmin]

Audit-confirmed P0. PENDING_STUCK_BACKSTOP_MS=300s (app.jsx:246) is below the system's own healthy budgets: cold-open ~300s measured / 400–500s budget (lib_beat_driver.sh clawdnd_dm_timeout), play.sh timeout+retry ≈400s. False 'stuck' re-opens the action bar + retryStuck re-POSTs → the same intent resolves twice. Fix in flight: budget-aware ceiling (firstBeat ≥540s, later ≥420s) + the missing healthy-350–450s red test. Ref #745 #746.

[100yenadmin]

Verified STALE-FIXED at HEAD 8c22f0b (v1.0.4 Beta triage / partial-Refs re-verify, 2026-06-15): FIXED at HEAD. The flat sub-budget 300s value the issue cites (old app.jsx:246) is GONE. viewer/openworlds/app.jsx:256-257 — PENDING_STUCK_BACKSTOP_MS=7min (≥ the ~400s play.sh timeout+retry budget) and PENDING_STUCK_BACKSTOP_FIRST_MS=9min (≥ the 400-500s cold-open budget); stuck

Closing as already-resolved (the ~50 PRs merged this session + the prior audit-fix waves landed it). Reopen if a fresh playtest reproduces.