diff --git a/packages/agents/content/skills/orchestrate/SKILL.md b/packages/agents/content/skills/orchestrate/SKILL.md
index 7330034e..a6f266ee 100644
--- a/packages/agents/content/skills/orchestrate/SKILL.md
+++ b/packages/agents/content/skills/orchestrate/SKILL.md
@@ -448,7 +448,7 @@ Include:
 
 After writing the artifact, call `register_artifact` for the run-summary artifact. Present the same summary to the user in the conversation. The conversational output should match the artifact content — do not abbreviate or omit sections.
 
-Call MCP tool `complete_run` with `{ runDir: {run-dir}, status: "completed" | "failed" | "needs_manual_review" }`. This emits a `run_completed` event and stamps `completedAt` on the run-index.json header. The `status` field within the event carries the actual outcome (`completed`, `failed`, or `needs_manual_review`).
+Call MCP tool `complete_run` with `{ runDir: {run-dir}, status: "completed" | "failed" | "needs_manual_review", reason?: string }`. When `status` is `"failed"`, this emits a `run_failed` event (the optional `reason` field is included if provided); otherwise it emits a `run_completed` event. Either way, `completedAt` is stamped on the run-index.json header.
 
 ## Phase 6: Wrap-up (prompted, conditional)
 
diff --git a/packages/mcp/src/server.ts b/packages/mcp/src/server.ts
index 6342e5f7..e226ae14 100644
--- a/packages/mcp/src/server.ts
+++ b/packages/mcp/src/server.ts
@@ -91,10 +91,12 @@ export function createServer(): McpServer {
   server.registerTool(
     'complete_run',
     {
-      description: 'Complete a run: emit run_completed event and stamp completedAt on run-index.json.',
+      description:
+        'Complete a run: emit run_completed (or run_failed when status is failed) event and stamp completedAt on run-index.json.',
       inputSchema: {
         runDir: z.string(),
         status: z.enum(['completed', 'failed', 'needs_manual_review']),
+        reason: z.string().optional(),
       },
     },
     async (args) => {
diff --git a/packages/mcp/src/tools/__tests__/complete-run.test.ts b/packages/mcp/src/tools/__tests__/complete-run.test.ts
index 02ffdd35..50372229 100644
--- a/packages/mcp/src/tools/__tests__/complete-run.test.ts
+++ b/packages/mcp/src/tools/__tests__/complete-run.test.ts
@@ -54,7 +54,7 @@ describe('completeRun', () => {
     expect(result.error).toContain('must be one of');
   });
 
-  it('accepts failed status', async () => {
+  it('emits run_failed event when status is failed', async () => {
     const runDir = await createRunDir();
     const result = await completeRun({ runDir, status: 'failed' });
 
@@ -62,7 +62,31 @@ describe('completeRun', () => {
 
     const content = await readFile(join(runDir, 'run-log.jsonl'), 'utf8');
     const event: unknown = JSON.parse(content.trim());
-    expect(event).toMatchObject({ status: 'failed' });
+    expect(event).toMatchObject({ event: 'run_failed', status: 'failed' });
+    expect(event).not.toHaveProperty('reason');
+  });
+
+  it('includes reason in run_failed event', async () => {
+    const runDir = await createRunDir();
+    const result = await completeRun({ runDir, status: 'failed', reason: 'TypeScript compilation errors' });
+
+    expect(result.success).toBe(true);
+
+    const content = await readFile(join(runDir, 'run-log.jsonl'), 'utf8');
+    const event: unknown = JSON.parse(content.trim());
+    expect(event).toMatchObject({ event: 'run_failed', status: 'failed', reason: 'TypeScript compilation errors' });
+  });
+
+  it('ignores reason when status is not failed', async () => {
+    const runDir = await createRunDir();
+    const result = await completeRun({ runDir, status: 'completed', reason: 'should be ignored' });
+
+    expect(result.success).toBe(true);
+
+    const content = await readFile(join(runDir, 'run-log.jsonl'), 'utf8');
+    const event: unknown = JSON.parse(content.trim());
+    expect(event).toMatchObject({ event: 'run_completed', status: 'completed' });
+    expect(event).not.toHaveProperty('reason');
   });
 
   it('accepts needs_manual_review status', async () => {
@@ -73,7 +97,7 @@ describe('completeRun', () => {
 
     const content = await readFile(join(runDir, 'run-log.jsonl'), 'utf8');
     const event: unknown = JSON.parse(content.trim());
-    expect(event).toMatchObject({ status: 'needs_manual_review' });
+    expect(event).toMatchObject({ event: 'run_completed', status: 'needs_manual_review' });
   });
 
   it('rejects when run-index.json is missing', async () => {
diff --git a/packages/mcp/src/tools/complete-run.ts b/packages/mcp/src/tools/complete-run.ts
index 828040a0..38b2a9e1 100644
--- a/packages/mcp/src/tools/complete-run.ts
+++ b/packages/mcp/src/tools/complete-run.ts
@@ -13,6 +13,7 @@ export type CompletionStatus = z.infer<typeof completionStatusSchema>;
 export interface CompleteRunInput {
   runDir: string;
   status: string;
+  reason?: string | undefined;
 }
 
 export interface CompleteRunResult {
@@ -21,11 +22,16 @@ export interface CompleteRunResult {
 }
 
 /**
- * Complete a run: emit a `run_completed` event and stamp `completedAt` on the
- * run-index.json header for fast discovery without reading the JSONL log.
+ * Complete a run: emit a `run_completed` or `run_failed` event (based on the
+ * status) and stamp `completedAt` on the run-index.json header for fast
+ * discovery without reading the JSONL log.
+ *
+ * When `status` is `'failed'`, a `run_failed` event is emitted instead of
+ * `run_completed`. The optional `reason` field is included in the `run_failed`
+ * event; it is ignored for other statuses.
  */
 export async function completeRun(input: CompleteRunInput): Promise<CompleteRunResult> {
-  const { runDir, status } = input;
+  const { runDir, status, reason } = input;
 
   const statusResult = completionStatusSchema.safeParse(status);
   if (!statusResult.success) {
@@ -40,10 +46,15 @@ export async function completeRun(input: CompleteRunInput): Promise<CompleteRunR
   // Capture timestamp once so the event and the index header are consistent
   const now = new Date().toISOString();
 
-  // Emit run_completed event
+  // Emit run_failed for failed status, run_completed otherwise
+  const event =
+    validStatus === 'failed'
+      ? { event: 'run_failed', status: validStatus, reason }
+      : { event: 'run_completed', status: validStatus };
+
   const emitResult = await emitEvent({
     runDir,
-    event: { event: 'run_completed', status: validStatus },
+    event,
     timestamp: now,
   });