diff --git a/packages/sdk/src/__tests__/workflow-trajectory.test.ts b/packages/sdk/src/__tests__/workflow-trajectory.test.ts
index f9fe21361..9c19b6558 100644
--- a/packages/sdk/src/__tests__/workflow-trajectory.test.ts
+++ b/packages/sdk/src/__tests__/workflow-trajectory.test.ts
@@ -32,15 +32,32 @@ function readTrajectoryFile(dir: string): any {
   return JSON.parse(readFileSync(path.join(activeDir, jsonFiles[0]), 'utf-8'));
 }
 
-function readCompletedTrajectoryFile(dir: string): any {
+function findCompletedTrajectoryJson(dir: string): string | null {
   const completedDir = path.join(dir, '.trajectories', 'completed');
   if (!existsSync(completedDir)) return null;
 
-  const files = readdirSync(completedDir);
-  const jsonFiles = files.filter((f: string) => f.endsWith('.json'));
-  if (jsonFiles.length === 0) return null;
+  // Completed trajectories now live under completed/YYYY-MM/. Walk the
+  // tree so tests don't have to know the exact bucket name.
+  const stack: string[] = [completedDir];
+  while (stack.length > 0) {
+    const current = stack.pop() as string;
+    const entries = readdirSync(current, { withFileTypes: true });
+    for (const entry of entries) {
+      const entryPath = path.join(current, entry.name);
+      if (entry.isDirectory()) {
+        stack.push(entryPath);
+      } else if (entry.isFile() && entry.name.endsWith('.json')) {
+        return entryPath;
+      }
+    }
+  }
+  return null;
+}
 
-  return JSON.parse(readFileSync(path.join(completedDir, jsonFiles[0]), 'utf-8'));
+function readCompletedTrajectoryFile(dir: string): any {
+  const jsonPath = findCompletedTrajectoryJson(dir);
+  if (!jsonPath) return null;
+  return JSON.parse(readFileSync(jsonPath, 'utf-8'));
 }
 
 // ── Tests ────────────────────────────────────────────────────────────────────
@@ -135,6 +152,34 @@ describe('WorkflowTrajectory', () => {
       expect(completed).toBeTruthy();
       expect(completed.status).toBe('abandoned');
     });
+
+    it('should write completed files under completed/YYYY-MM/', async () => {
+      const traj = new WorkflowTrajectory({}, 'run-abc', tmpDir);
+      await traj.start('my-workflow', 2);
+      await traj.complete('All done', 0.95);
+
+      const jsonPath = findCompletedTrajectoryJson(tmpDir);
+      expect(jsonPath).not.toBeNull();
+
+      // Relative path from .trajectories/completed must have exactly one
+      // intermediate directory matching YYYY-MM.
+      const completedRoot = path.join(tmpDir, '.trajectories', 'completed');
+      const rel = path.relative(completedRoot, jsonPath as string);
+      const segments = rel.split(path.sep);
+      expect(segments).toHaveLength(2);
+      expect(segments[0]).toMatch(/^\d{4}-\d{2}$/);
+      expect(segments[1]).toMatch(/^traj_.*\.json$/);
+    });
+
+    it('should populate canonical empty arrays on start', async () => {
+      const traj = new WorkflowTrajectory({}, 'run-abc', tmpDir);
+      await traj.start('my-workflow', 2);
+
+      const data = readTrajectoryFile(tmpDir);
+      expect(data.commits).toEqual([]);
+      expect(data.filesChanged).toEqual([]);
+      expect(data.tags).toEqual([]);
+    });
   });
 
   // ── Step events ────────────────────────────────────────────────────────
@@ -143,10 +188,7 @@ describe('WorkflowTrajectory', () => {
     it('should record step started', async () => {
       const traj = new WorkflowTrajectory({}, 'run-1', tmpDir);
       await traj.start('wf', 2);
-      await traj.stepStarted(
-        { name: 'build', agent: 'builder', task: 'Build it' },
-        'builder-agent',
-      );
+      await traj.stepStarted({ name: 'build', agent: 'builder', task: 'Build it' }, 'builder-agent');
 
       const data = readTrajectoryFile(tmpDir);
       expect(data.agents).toHaveLength(2); // orchestrator + builder-agent
@@ -157,11 +199,7 @@ describe('WorkflowTrajectory', () => {
     it('should record step completed', async () => {
       const traj = new WorkflowTrajectory({}, 'run-1', tmpDir);
       await traj.start('wf', 1);
-      await traj.stepCompleted(
-        { name: 'test', agent: 'tester', task: 'Run tests' },
-        'All tests passing',
-        1,
-      );
+      await traj.stepCompleted({ name: 'test', agent: 'tester', task: 'Run tests' }, 'All tests passing', 1);
 
       const data = readTrajectoryFile(tmpDir);
       const events = data.chapters.flatMap((c: any) => c.events);
@@ -175,7 +213,7 @@ describe('WorkflowTrajectory', () => {
         { name: 'deploy', agent: 'deployer', task: 'Deploy' },
         'Connection refused',
         1,
-        3,
+        3
       );
 
       const data = readTrajectoryFile(tmpDir);
@@ -186,10 +224,7 @@ describe('WorkflowTrajectory', () => {
     it('should record step skipped', async () => {
       const traj = new WorkflowTrajectory({}, 'run-1', tmpDir);
       await traj.start('wf', 2);
-      await traj.stepSkipped(
-        { name: 'integration', agent: 'tester', task: 'Test' },
-        'Upstream failed',
-      );
+      await traj.stepSkipped({ name: 'integration', agent: 'tester', task: 'Test' }, 'Upstream failed');
 
       const data = readTrajectoryFile(tmpDir);
       const events = data.chapters.flatMap((c: any) => c.events);
diff --git a/packages/sdk/src/workflows/trajectory.ts b/packages/sdk/src/workflows/trajectory.ts
index eef05eb77..bccf4d991 100644
--- a/packages/sdk/src/workflows/trajectory.ts
+++ b/packages/sdk/src/workflows/trajectory.ts
@@ -66,6 +66,15 @@ interface TrajectoryFile {
     learnings?: string[];
     challenges?: string[];
   };
+  /**
+   * Canonical top-level fields the `agent-trajectories` schema declares
+   * (as `.default([])` / `.optional()`). We populate them here so the
+   * written files are canonical-complete and round-trip cleanly through
+   * any stricter future reader.
+   */
+  commits: string[];
+  filesChanged: string[];
+  tags: string[];
 }
 
 // ── Step state for synthesis ─────────────────────────────────────────────────
@@ -191,6 +200,9 @@ export class WorkflowTrajectory {
       startedAt: new Date().toISOString(),
       agents: [{ name: 'orchestrator', role: 'workflow-runner', joinedAt: new Date().toISOString() }],
       chapters: [],
+      commits: [],
+      filesChanged: [],
+      tags: [],
     };
 
     // Open Planning chapter — record intent, not just mechanics
@@ -765,7 +777,20 @@ export class WorkflowTrajectory {
 
     try {
       const activeDir = path.join(this.dataDir, 'active');
-      const completedDir = path.join(this.dataDir, 'completed');
+      // Match the canonical `agent-trajectories` layout: completed files
+      // live under `completed/YYYY-MM/` based on completedAt (falling back
+      // to startedAt). Before this change we wrote to the flat
+      // `completed/` root, which worked but diverged from what
+      // `FileStorage.save()` produces and forced the reader to grow a
+      // legacy-layout fallback. Aligning the writer lets the reader shed
+      // that branch over time.
+      const bucketSource = this.trajectory.completedAt ?? this.trajectory.startedAt;
+      const bucketDate = new Date(bucketSource);
+      const monthBucket = `${bucketDate.getUTCFullYear()}-${String(bucketDate.getUTCMonth() + 1).padStart(
+        2,
+        '0'
+      )}`;
+      const completedDir = path.join(this.dataDir, 'completed', monthBucket);
       await mkdir(completedDir, { recursive: true });
 
       const activePath = path.join(activeDir, `${this.trajectory.id}.json`);