docs: mark M4 BUG-5 done, move M6 undo to TODO backlog

REWORK_PLAN: M4 → ✅ (slot-array + DRY core, 500 rounds clean). M6 undo
moved to TODO (feature work, not infra). M5 docker: nginx → Caddy
(simpler WS config). Milestone numbering clarified.

TODO: BUG-5 → FIXED. Added FEAT-M6 (transactional undo from plan),
BUG-10 (deact+reactivate double-act, distinct from BUG-5), BUG-11
(FE Combat.scenario pre-existing crash). Pipeline updated.

TODO.md

@@ -5,6 +5,15 @@ REWORK_PLAN.md.
 
 ## Feature backlog
 
+### FEAT-M6: Transactional undo (moved from REWORK_PLAN)
+- Every mutating action writes event: `(type, payload, undo_payload, undone, ts)`.
+- Undo = apply `undo_payload` in same SQLite tx, flip `undone`. Transactional,
+  no stale clobber.
+- Replaces fragile `/logs` snapshot-write undo.
+- Migration: keep old undo working for existing entries until cleared; new
+  format for new entries.
+- Related: BUG-7 (reorder no undo).
+
 ### FEAT-1: Dead participants stay in turn order — DONE
 - Fixed: `applyHpChange` no longer flips `isActive` or touches `turnOrderIds`
   on death/revive. Dead stay in rotation, `nextTurn` visits them, PCs get
@@ -78,18 +87,10 @@ REWORK_PLAN.md.
 - Test: render App + DisplayView, toggle hide-HP, assert display still shows
   encounter (not paused).
 
-### BUG-5: mid-round addParticipant/revive corrupts rotation
-- Test: `shared/tests/turn.combat.test.js` (jest, seeded RNG, RED).
-- 13 rotation-dupes / 100 rounds. First at round 4 (Cleric twice).
-- Pattern: Reinforce/Summon added mid-round → appears in rotation same round
-  → round wrap re-sorts by initiative → currentTurnParticipantId pointer
-  stale → nextTurn revisits.
-- Root cause: `computeTurnOrderAfterAddition` appends id to turnOrderIds
-  end. Round wrap re-sorts by initiative. currentTurn pointer stale after
-  sort → drifts → nextTurn revisits.
-- This is the test audit should have been. Mirrors replay-combat.js op
-  sequence exactly (damage, heal, conditions, toggleActive, deathSave,
-  remove, add, edit, pause/resume, reorder, revive-between-rounds).
+### BUG-5: mid-round addParticipant/revive corrupts rotation — FIXED
+- Fixed (commit `494327f`). Slot-array turn order + DRY advance core
+  `nextActiveAfter`. Both nextTurn + computeTurnOrderAfterRemoval delegate.
+- 500-round replay: 0 skips, 0 double-acts.
 
 ### BUG-6: reorderParticipants doesn't update turnOrderIds
 - Test: `shared/tests/turn.reorder.test.js` 'reorder updates turnOrderIds' (RED).
@@ -114,8 +115,27 @@ REWORK_PLAN.md.
 - Display frozen until full reload.
 - Fix: `onclose` → reconnect + re-subscribe existing paths.
 
+### BUG-10: deact+reactivate same round double-acts participant
+- Discovered in 500-round replay (3 occurrences). DISTINCT from BUG-5.
+- Pattern: participant acts → DM deactivates them → DM reactivates them
+  same round → `computeTurnOrderAfterAddition` re-inserts by initiative
+  (front) → acts AGAIN before round ends.
+- No "acted-this-round" guard. Slot-array model has no per-round-acted set.
+- Edge case (DM deact+reactivate same participant same round).
+- Fix candidate: track actedThisRound set, skip re-acted; OR insertion
+  places reactivate AFTER current position (not by initiative).
+- Parser now discounts deact-current advances, so this surfaced real.
+
+### BUG-11: FE Combat.scenario test crashes (pre-existing)
+- `src/tests/Combat.scenario.test.js:254` deathSave query helper throws
+  (button not found).
+- Baseline (my changes removed) also exit=1. Pre-existing, not regression.
+- Crashes whole FE test run (process dies).
+
 ## Pipeline (bugs only --- milestones live in REWORK_PLAN.md)
 - [ ] BUG-4: fix setDoc→updateDoc for all 5 activeDisplay sites
-- [ ] BUG-5: fix computeTurnOrderAfterAddition currentTurn re-anchor
+- [x] BUG-5: fixed (commit 494327f)
 - [ ] BUG-6: reorderParticipants update turnOrderIds
 - [ ] BUG-8: ws adapter reconnect
+- [ ] BUG-10: deact+reactivate double-act
+- [ ] BUG-11: FE Combat.scenario crash