diff --git a/TODO.md b/TODO.md
index c117de4..b3adffd 100644
--- a/TODO.md
+++ b/TODO.md
@@ -8,15 +8,6 @@ Backlog of bugs + long-term items. Milestones live in REWORK_PLAN.md.
 - `reorderParticipants` returns `log: null`. Other ops return `log.undo`.
 - Cannot undo drag-drop. Candidate for undo system (M6).
 
-### 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 → 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).
-
 ### BUG-13: reorderParticipants crossing current pointer = ambiguous acted-semantics
 - `reorderParticipants` (shared/turn.js) = pure drag, no pointer logic.
 - Swapping two actors across current pointer mid-round = ambiguous
@@ -95,6 +86,10 @@ Backlog of bugs + long-term items. Milestones live in REWORK_PLAN.md.
 ### BUG-8: server adapter has no reconnect
 - FIXED — onclose reconnects + re-subscribes existing paths.
 
+### BUG-10: deact+reactivate same round double-acts participant
+- FIXED — 1-list model keeps slot position on toggle. Reactivate does not
+  grant second turn. Test: turn.bug10.test.js.
+
 ### BUG-11: FE Combat.scenario test crashes
 - FIXED — moved to shared/turn.combat.test.js, pure functions, 100 rounds.
 
diff --git a/shared/tests/turn.bug10.test.js b/shared/tests/turn.bug10.test.js
new file mode 100644
index 0000000..07f0ef3
--- /dev/null
+++ b/shared/tests/turn.bug10.test.js
@@ -0,0 +1,82 @@
+// BUG-10: deact+reactivate same round double-acts participant.
+// OLD bug: reactivation re-inserted by initiative (front of pointer) →
+// participant acted again before round end.
+//
+// 1-list model: toggleActive keeps slot position. Reactivation does NOT
+// grant second turn. Each participant acts at most once per round.
+//
+// Test: walk rounds, count visits. Deactivate+reactivate mid-round must
+// not cause any participant to act twice in same round.
+
+'use strict';
+
+const shared = require('@ttrpg/shared');
+const {
+  makeParticipant,
+  startEncounter, nextTurn, toggleParticipantActive,
+} = shared;
+
+function p(id, init) {
+  return makeParticipant({ id, name: id, type: 'monster',
+    initiative: init, maxHp: 100, currentHp: 100 });
+}
+function enc(ps) {
+  return { name:'t', participants:ps, isStarted:false, isPaused:false,
+    round:0, currentTurnParticipantId:null, turnOrderIds:[] };
+}
+const apply = (e, r) => r && r.patch ? { ...e, ...r.patch } : e;
+
+describe('BUG-10: deact+reactivate same round', () => {
+  test('no participant acts twice in a round after deact+reactivate', () => {
+    // [a(10), b(7), c(3)]
+    let e = enc([p('a',10),p('b',7),p('c',3)]);
+    e = apply(e, startEncounter(e)); // a current, r1
+
+    const r1 = [];
+    r1.push(e.currentTurnParticipantId); // a acts
+    e = apply(e, nextTurn(e)); r1.push(e.currentTurnParticipantId); // b acts
+
+    // b already acted. Deactivate b (NOT current now — b just became current
+    // via nextTurn, so b IS current). Toggle off advances pointer to c.
+    e = apply(e, toggleParticipantActive(e, 'b')); // b off
+    // current advanced to c (b was current)
+    r1.push(e.currentTurnParticipantId); // c "becomes" active turn
+    // reactivate b same round
+    e = apply(e, toggleParticipantActive(e, 'b')); // b on
+
+    // nextTurn from c → round 2 (a). b must NOT re-act in round 1.
+    e = apply(e, nextTurn(e));
+    expect(e.round).toBe(2);
+    expect(e.currentTurnParticipantId).toBe('a');
+
+    // b acted once in r1, must act once in r2
+    e = apply(e, nextTurn(e));
+    expect(e.currentTurnParticipantId).toBe('b');
+    e = apply(e, nextTurn(e));
+    expect(e.currentTurnParticipantId).toBe('c');
+
+    // per-round visit count
+    const bCountR1 = r1.filter(id => id === 'b').length;
+    expect(bCountR1).toBe(1);
+  });
+
+  test('deactivate+reactivate non-current who already acted: no re-act', () => {
+    // [a(10), b(7), c(3)]. a acts, b acts, c acts (round 1 done).
+    // Then deactivate a (already acted, not current since c is current).
+    // Reactivate a. a must not act again until round 2.
+    let e = enc([p('a',10),p('b',7),p('c',3)]);
+    e = apply(e, startEncounter(e)); // a
+    e = apply(e, nextTurn(e)); // b
+    e = apply(e, nextTurn(e)); // c (r1 full: a,b,c)
+    // c is current. deactivate a (not current, already acted).
+    e = apply(e, toggleParticipantActive(e, 'a')); // a off, pointer stays c
+    expect(e.currentTurnParticipantId).toBe('c');
+    e = apply(e, toggleParticipantActive(e, 'a')); // a on
+    expect(e.currentTurnParticipantId).toBe('c');
+
+    // nextTurn from c → a (round 2). a acts in r2, once.
+    e = apply(e, nextTurn(e));
+    expect(e.round).toBe(2);
+    expect(e.currentTurnParticipantId).toBe('a');
+  });
+});