fix(todo-continuation-enforcer): make compaction guard epoch-aware

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/hooks/todo-continuation-enforcer/compaction-guard.regression.test.ts

@@ -0,0 +1,67 @@
+import { describe, expect, it as test } from "bun:test"
+
+import { COMPACTION_GUARD_MS } from "./constants"
+import {
+  acknowledgeCompactionGuard,
+  armCompactionGuard,
+  isCompactionGuardActive,
+} from "./compaction-guard"
+import type { SessionState } from "./types"
+
+function createSessionState(): SessionState {
+  return {
+    stagnationCount: 0,
+    consecutiveFailures: 0,
+  }
+}
+
+describe("compaction guard regressions", () => {
+  describe("#given a compaction epoch was already acknowledged", () => {
+    describe("#when a newer compaction epoch is armed", () => {
+      test("#then the guard re-arms for the newer epoch", () => {
+        const state = createSessionState()
+
+        const firstEpoch = armCompactionGuard(state, 1_000)
+        expect(acknowledgeCompactionGuard(state, firstEpoch)).toBe(true)
+        expect(isCompactionGuardActive(state, 1_001)).toBe(false)
+
+        const secondEpoch = armCompactionGuard(state, 2_000)
+
+        expect(secondEpoch).toBe(firstEpoch + 1)
+        expect(state.recentCompactionEpoch).toBe(secondEpoch)
+        expect(isCompactionGuardActive(state, 2_001)).toBe(true)
+      })
+    })
+  })
+
+  describe("#given a newer compaction epoch is armed before an older idle check finishes", () => {
+    describe("#when the older epoch tries to acknowledge the guard", () => {
+      test("#then it does not clear the newer epoch", () => {
+        const state = createSessionState()
+
+        const firstEpoch = armCompactionGuard(state, 1_000)
+        const secondEpoch = armCompactionGuard(state, 2_000)
+
+        expect(acknowledgeCompactionGuard(state, firstEpoch)).toBe(false)
+        expect(state.acknowledgedCompactionEpoch).toBeUndefined()
+        expect(state.recentCompactionEpoch).toBe(secondEpoch)
+        expect(isCompactionGuardActive(state, 2_001)).toBe(true)
+      })
+    })
+  })
+
+  describe("#given the current compaction epoch is still inside the guard window", () => {
+    describe("#when that same epoch is acknowledged", () => {
+      test("#then continuation can proceed again without waiting for the window to expire", () => {
+        const state = createSessionState()
+
+        const currentEpoch = armCompactionGuard(state, 1_000)
+
+        expect(isCompactionGuardActive(state, 1_000 + COMPACTION_GUARD_MS - 1)).toBe(true)
+        expect(acknowledgeCompactionGuard(state, currentEpoch)).toBe(true)
+        expect(isCompactionGuardActive(state, 1_001)).toBe(false)
+        expect(isCompactionGuardActive(state, 1_000 + COMPACTION_GUARD_MS - 1)).toBe(false)
+      })
+    })
+  })
+})