fix(todo-continuation-enforcer): track continuation stagnation state

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

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

src/hooks/todo-continuation-enforcer/session-state.test.ts

@@ -0,0 +1,49 @@
+import { afterEach, beforeEach, describe, expect, test } from "bun:test"
+
+import { createSessionStateStore, type SessionStateStore } from "./session-state"
+
+describe("createSessionStateStore", () => {
+  let sessionStateStore: SessionStateStore
+
+  beforeEach(() => {
+    sessionStateStore = createSessionStateStore()
+  })
+
+  afterEach(() => {
+    sessionStateStore.shutdown()
+  })
+
+  test("given repeated incomplete counts after a continuation, tracks stagnation", () => {
+    // given
+    const sessionID = "ses-stagnation"
+    const state = sessionStateStore.getState(sessionID)
+    state.lastInjectedAt = Date.now()
+
+    // when
+    const firstUpdate = sessionStateStore.trackContinuationProgress(sessionID, 2)
+    const secondUpdate = sessionStateStore.trackContinuationProgress(sessionID, 2)
+    const thirdUpdate = sessionStateStore.trackContinuationProgress(sessionID, 2)
+
+    // then
+    expect(firstUpdate.stagnationCount).toBe(0)
+    expect(secondUpdate.stagnationCount).toBe(1)
+    expect(thirdUpdate.stagnationCount).toBe(2)
+  })
+
+  test("given incomplete count decreases, resets stagnation tracking", () => {
+    // given
+    const sessionID = "ses-progress-reset"
+    const state = sessionStateStore.getState(sessionID)
+    state.lastInjectedAt = Date.now()
+    sessionStateStore.trackContinuationProgress(sessionID, 3)
+    sessionStateStore.trackContinuationProgress(sessionID, 3)
+
+    // when
+    const progressUpdate = sessionStateStore.trackContinuationProgress(sessionID, 2)
+
+    // then
+    expect(progressUpdate.hasProgressed).toBe(true)
+    expect(progressUpdate.stagnationCount).toBe(0)
+    expect(sessionStateStore.getState(sessionID).lastIncompleteCount).toBe(2)
+  })
+})