diff --git a/package-lock.json b/package-lock.json
index e7d3738..833eb96 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -7769,7 +7769,8 @@
         "@types/node": "^25.5.0",
         "esbuild": "^0.27.0",
         "tsx": "^4.21.0",
-        "typescript": "^5.9.3"
+        "typescript": "^5.9.3",
+        "vitest": "^4.1.0"
       },
       "engines": {
         "node": ">=22.13"
diff --git a/package.json b/package.json
index c222123..9a06edc 100644
--- a/package.json
+++ b/package.json
@@ -14,7 +14,7 @@
   "scripts": {
     "build": "tsx scripts/build.ts",
     "build:skills": "tsx scripts/build-skills.ts",
-    "test": "npm run test -w @diffity/git && npm run test -w @diffity/github && npm run test -w @diffity/parser && npm run test -w @diffity/ui && npm run test:scripts",
+    "test": "npm run test -w @diffity/git && npm run test -w @diffity/github && npm run test -w @diffity/parser && npm run test -w @diffity/ui && npm run test -w diffity && npm run test:scripts",
     "link-dev": "tsx scripts/link-dev.ts",
     "dev": "tsx scripts/dev.ts",
     "release:patch": "npm run build && tsx scripts/release.ts patch && npm publish -w packages/cli",
diff --git a/packages/cli/package.json b/packages/cli/package.json
index 3590a6b..db29f2d 100644
--- a/packages/cli/package.json
+++ b/packages/cli/package.json
@@ -9,7 +9,9 @@
   "scripts": {
     "build": "tsx build.ts",
     "dev": "tsx src/index.ts",
-    "dev:watch": "tsx build.ts --watch"
+    "dev:watch": "tsx build.ts --watch",
+    "test": "vitest run",
+    "test:watch": "vitest"
   },
   "dependencies": {
     "commander": "^14.0.3",
@@ -45,6 +47,7 @@
     "@types/node": "^25.5.0",
     "esbuild": "^0.27.0",
     "tsx": "^4.21.0",
-    "typescript": "^5.9.3"
+    "typescript": "^5.9.3",
+    "vitest": "^4.1.0"
   }
 }
diff --git a/packages/cli/src/session.ts b/packages/cli/src/session.ts
index a6bfd03..fa05100 100644
--- a/packages/cli/src/session.ts
+++ b/packages/cli/src/session.ts
@@ -30,16 +30,49 @@ export function findOrCreateSession(ref: string): Session {
     return session;
   }
 
+  // A session is identified by the commit as well as the ref, so committing creates a new
+  // one. Anything still open has to come with it: the whole point of reviewing your own
+  // change is to act on the findings, and acting on them moves HEAD.
+  const previous = queryOne<{ id: string }>(
+    'SELECT id FROM review_sessions WHERE ref = ? ORDER BY created_at DESC, rowid DESC LIMIT 1',
+    ref,
+  );
+
   const id = randomUUID();
   db.prepare(
     'INSERT INTO review_sessions (id, ref, head_hash) VALUES (?, ?, ?)'
   ).run(id, ref, headHash);
 
+  if (previous) {
+    carryForward(previous.id, id);
+  }
+
   const session: Session = { id, ref, headHash };
   writeFileSync(sessionFilePath(), JSON.stringify(session));
   return session;
 }
 
+/**
+ * Moves rather than copies, so thread ids stay stable and nothing is duplicated. Threads that
+ * were resolved or dismissed stay behind: they belong to the commit where they were dealt with,
+ * and reopening them on every later commit would be noise.
+ *
+ * Line numbers are not re-anchored yet, so a thread whose code moved still points at the line
+ * it was written against.
+ */
+export function carryForward(fromSessionId: string, toSessionId: string): void {
+  const db = getDb();
+
+  db.prepare(
+    "UPDATE comment_threads SET session_id = ? WHERE session_id = ? AND status = 'open'",
+  ).run(toSessionId, fromSessionId);
+
+  db.prepare('UPDATE tours SET session_id = ? WHERE session_id = ?').run(
+    toSessionId,
+    fromSessionId,
+  );
+}
+
 export function getCurrentSession(): Session | null {
   try {
     const raw = readFileSync(sessionFilePath(), 'utf-8');
diff --git a/packages/cli/tests/session-continuity.test.ts b/packages/cli/tests/session-continuity.test.ts
new file mode 100644
index 0000000..30f09c3
--- /dev/null
+++ b/packages/cli/tests/session-continuity.test.ts
@@ -0,0 +1,85 @@
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import { execFileSync } from 'node:child_process';
+import { mkdtempSync, writeFileSync, rmSync } from 'node:fs';
+import { join } from 'node:path';
+import { tmpdir } from 'node:os';
+
+let root: string;
+let repoDir: string;
+let origCwd: string;
+
+function git(args: string[]): string {
+  return execFileSync('git', args, { cwd: repoDir, encoding: 'utf-8', stdio: 'pipe' }).trim();
+}
+
+function commit(name: string): void {
+  writeFileSync(join(repoDir, name), `${name}\n`);
+  git(['add', '.']);
+  git(['commit', '-m', name]);
+}
+
+beforeAll(() => {
+  origCwd = process.cwd();
+  root = mkdtempSync(join(tmpdir(), 'diffity-session-'));
+  repoDir = join(root, 'repo');
+
+  execFileSync('git', ['init', '-b', 'main', repoDir], { stdio: 'pipe' });
+  execFileSync('git', ['config', 'user.email', 'test@test.com'], { cwd: repoDir, stdio: 'pipe' });
+  execFileSync('git', ['config', 'user.name', 'Test'], { cwd: repoDir, stdio: 'pipe' });
+  commit('a.txt');
+
+  // Set before anything opens the database, which resolves its path once.
+  process.env.DIFFITY_DATA_DIR = join(root, 'notes');
+  process.chdir(repoDir);
+});
+
+afterAll(() => {
+  process.chdir(origCwd);
+  delete process.env.DIFFITY_DATA_DIR;
+  rmSync(root, { recursive: true, force: true });
+});
+
+describe('a session when HEAD moves', () => {
+  it('brings open threads and walkthroughs with it, and leaves closed ones behind', async () => {
+    const { findOrCreateSession } = await import('../src/session.js');
+    const { createThread, getThreadsForSession, updateThreadStatus } = await import('../src/threads.js');
+    const { createTour, getToursForSession } = await import('../src/tours.js');
+
+    const first = findOrCreateSession('work');
+    const open = createThread(first.id, 'a.txt', 'new', 1, 1, 'P1: still a problem', {
+      name: 'Agent',
+      type: 'agent',
+    });
+    const dealtWith = createThread(first.id, 'a.txt', 'new', 2, 2, 'P2: fixed already', {
+      name: 'Agent',
+      type: 'agent',
+    });
+    updateThreadStatus(dealtWith.id, 'resolved');
+    const tour = createTour(first.id, 'Reading order', '');
+
+    // Acting on a finding is what moves HEAD.
+    commit('b.txt');
+    const second = findOrCreateSession('work');
+
+    expect(second.id).not.toBe(first.id);
+
+    const carried = getThreadsForSession(second.id);
+    expect(carried.map(thread => thread.id)).toEqual([open.id]);
+    expect(getToursForSession(second.id).map(t => t.id)).toEqual([tour.id]);
+
+    const left = getThreadsForSession(first.id);
+    expect(left.map(thread => thread.id)).toEqual([dealtWith.id]);
+  });
+
+  it('returns the same session while HEAD stays put', async () => {
+    const { findOrCreateSession } = await import('../src/session.js');
+
+    expect(findOrCreateSession('work').id).toBe(findOrCreateSession('work').id);
+  });
+
+  it('keeps refs apart', async () => {
+    const { findOrCreateSession } = await import('../src/session.js');
+
+    expect(findOrCreateSession('work').id).not.toBe(findOrCreateSession('main').id);
+  });
+});