Docs: exploding-barrels Build Spec + session log Part J + roadmap tick

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Docs/Vault/06_Roadmap/Iteration_2026-07_CoopHades.md

@@ -145,8 +145,11 @@ attacks/animations/effects**. Art direction deliberately UNDECIDED — lighting
 
 ### Long-term (server-sim; adversarial design-review REQUIRED per slice)
 
-7. **Environmental hazards:** exploding barrels, Blight geysers, trap tiles — damage BOTH sides so enemies can be
-   baited into them. Real combat interplay; replication + predicted-damage surface needs the review.
+7. **Environmental hazards — v1 SHIPPED (2026-07-10, `cd607ae15`, review-first `wf_2cb10454-fdf`):**
+   exploding barrels — ~25% of clutter seeds explosive; pop lights a ~0.6s FUSE (replicated Remaining=0 =
+   the client cue, strobing red glow) then radius-damages BOTH sides (bait mechanic; escapable). Zero new
+   replication. Geysers/trap tiles = later hazard variants on the same HazardExplosionSystem chassis.
+   See [[Exploding_Barrels_Build_Spec]].
 8. **Destructible cover:** in-room cover rocks take damage and crumble (Charger smashes through, players carve LOS).
    Structures already have Health; **re-validate the enemy stuck-fix backstop when cover can disappear mid-fight.**