diff --git a/.changeset/fn-workflow-completion-summary.md b/.changeset/fn-workflow-completion-summary.md
new file mode 100644
index 0000000000..6b0ae46ee6
--- /dev/null
+++ b/.changeset/fn-workflow-completion-summary.md
@@ -0,0 +1,7 @@
+---
+"@runfusion/fusion": patch
+---
+
+summary: Record completion summaries for workflow-driven tasks.
+category: fix
+dev: Workflow graph completions and resumed workflow merge work items now backfill task.summary when no agent summary exists.
diff --git a/packages/engine/src/__tests__/workflow-task-runtime.test.ts b/packages/engine/src/__tests__/workflow-task-runtime.test.ts
index 03dfa53175..00caaf7dd3 100644
--- a/packages/engine/src/__tests__/workflow-task-runtime.test.ts
+++ b/packages/engine/src/__tests__/workflow-task-runtime.test.ts
@@ -1,4 +1,4 @@
-import { describe, expect, it } from "vitest";
+import { describe, expect, it, vi } from "vitest";
 import type { Settings, TaskDetail, WorkflowIr, WorkflowWorkItem, WorkflowWorkItemState } from "@fusion/core";
 
 import { WorkflowTaskRuntime, type WorkflowTaskRuntimeDeps } from "../workflow-task-runtime.js";
@@ -180,6 +180,72 @@ describe("WorkflowTaskRuntime", () => {
     expect(workflowSelectionReads).toBe(1);
   });
 
+  it("records a completion summary when a workflow run completes without fn_task_done", async () => {
+    const updates: Array<{ taskId: string; summary: string }> = [];
+    const logs: Array<{ taskId: string; action: string; detail?: string }> = [];
+    const completedTask = {
+      ...task,
+      title: "Ship workflow summaries",
+      steps: [
+        { title: "Implement summary persistence", status: "done" },
+        { title: "Verify workflow completion", status: "done" },
+      ],
+      modifiedFiles: ["packages/engine/src/workflow-task-runtime.ts"],
+    } as TaskDetail;
+    const runtime = new WorkflowTaskRuntime({
+      store: {
+        getTask: async () => completedTask,
+        getTaskWorkflowSelection: () => ({ workflowId: "WF-001", stepIds: [] }),
+        getWorkflowDefinition: async () => ({ ir: selectedIr() }),
+        updateTask: async (taskId, update) => {
+          updates.push({ taskId, summary: update.summary });
+        },
+        logEntry: async (taskId, action, detail) => {
+          logs.push({ taskId, action, detail });
+        },
+      },
+      primitives: recordingPrimitives([]),
+      runCustomNode: async () => ({ outcome: "success" }),
+      parseStepsDeps,
+    });
+
+    const result = await runtime.run(completedTask, flagOff);
+
+    expect(result.disposition).toBe("completed");
+    expect(updates).toEqual([
+      {
+        taskId: task.id,
+        summary: expect.stringContaining("Workflow completed: Ship workflow summaries."),
+      },
+    ]);
+    expect(updates[0]?.summary).toContain("Completed 2/2 task steps.");
+    expect(updates[0]?.summary).toContain("Changed files: packages/engine/src/workflow-task-runtime.ts.");
+    expect(logs).toEqual([
+      expect.objectContaining({ taskId: task.id, action: "Workflow completion summary recorded" }),
+    ]);
+  });
+
+  it("preserves an existing workflow completion summary", async () => {
+    const updateTask = vi.fn();
+    const summarizedTask = { ...task, summary: "Agent-authored completion summary." } as TaskDetail;
+    const runtime = new WorkflowTaskRuntime({
+      store: {
+        getTask: async () => summarizedTask,
+        getTaskWorkflowSelection: () => ({ workflowId: "WF-001", stepIds: [] }),
+        getWorkflowDefinition: async () => ({ ir: selectedIr() }),
+        updateTask,
+      },
+      primitives: recordingPrimitives([]),
+      runCustomNode: async () => ({ outcome: "success" }),
+      parseStepsDeps,
+    });
+
+    const result = await runtime.run(summarizedTask, flagOff);
+
+    expect(result.disposition).toBe("completed");
+    expect(updateTask).not.toHaveBeenCalled();
+  });
+
   it("preserves attachments through selected workflow execution", async () => {
     const calls: string[] = [];
     const attachments = [
@@ -721,6 +787,63 @@ describe("WorkflowTaskRuntime", () => {
     ]);
   });
 
+  it("backfills a workflow completion summary before resumed merge work items run", async () => {
+    const observed: { mergeAttempt?: number; mergeRunId?: string; mergeWorkflowId?: string } = {};
+    const updates: Array<{ taskId: string; summary: string }> = [];
+    const transitions: Array<{ id: string; state: WorkflowWorkItemState; patch?: Record<string, unknown> }> = [];
+    const workItem = {
+      id: "work-merge-summary",
+      runId: "run-merge-summary",
+      taskId: task.id,
+      nodeId: "merge-attempt",
+      kind: "merge",
+      state: "running",
+      attempt: 0,
+      retryAfter: null,
+      leaseOwner: "scheduler-a",
+      leaseExpiresAt: "2026-06-09T00:01:00.000Z",
+      lastError: null,
+      blockedReason: null,
+      createdAt: "2026-06-09T00:00:00.000Z",
+      updatedAt: "2026-06-09T00:00:00.000Z",
+    } satisfies WorkflowWorkItem;
+    const runtime = new WorkflowTaskRuntime({
+      store: {
+        getTask: async () => ({
+          ...task,
+          title: "Resume merge with summary",
+          steps: [{ title: "Finish work", status: "done" }],
+        } as TaskDetail),
+        getTaskWorkflowSelection: () => undefined,
+        getWorkflowDefinition: async () => undefined,
+        updateTask: async (taskId, update) => {
+          updates.push({ taskId, summary: update.summary });
+        },
+        transitionWorkflowWorkItem: (id, state, patch) => {
+          transitions.push({ id, state, patch });
+          return { ...workItem, state };
+        },
+      },
+      primitives: recordingPrimitives([], {}, observed),
+      runCustomNode: async () => ({ outcome: "success" }),
+    });
+
+    const result = await runtime.runWorkItem(workItem, flagOff);
+
+    expect(result.disposition).toBe("completed");
+    expect(updates).toEqual([
+      {
+        taskId: task.id,
+        summary: expect.stringContaining("Workflow completed: Resume merge with summary."),
+      },
+    ]);
+    expect(updates[0]?.summary).toContain("Completion source: workflow-work-item:merge (builtin:coding).");
+    expect(observed.mergeRunId).toBe("run-merge-summary");
+    expect(transitions).toEqual([
+      expect.objectContaining({ id: "work-merge-summary", state: "succeeded" }),
+    ]);
+  });
+
   it("uses the built-in workflow id in the default run id for unselected tasks", async () => {
     const observedRunIds: string[] = [];
     const runtime = new WorkflowTaskRuntime({
diff --git a/packages/engine/src/executor.ts b/packages/engine/src/executor.ts
index 4406aeaaa8..3d5ca90487 100644
--- a/packages/engine/src/executor.ts
+++ b/packages/engine/src/executor.ts
@@ -22,6 +22,7 @@ import {
   type WorkflowRunObservation,
 } from "@fusion/core";
 import { WorkflowGraphTaskRunner, type WorkflowGraphTaskRunResult } from "./workflow-graph-task-runner.js";
+import { ensureWorkflowCompletionSummary } from "./workflow-completion-summary.js";
 import { createCodeNodeRunner } from "./code-node-runner.js";
 import { getActiveNotificationService } from "./notifier.js";
 import type { ParseStepsHandlerDeps, CodeNodeRunner } from "./workflow-node-handlers.js";
@@ -2018,6 +2019,14 @@ export class TaskExecutor {
    */
   private async handoffTaskToReview(task: Task, reason: string, runId = this.getRunContextFor(task.id)?.runId): Promise<Task> {
     const agentId = this.getRunContextFor(task.id)?.agentId;
+    if (reason.startsWith("workflow-")) {
+      await ensureWorkflowCompletionSummary(this.store, task as TaskDetail, {
+        reason,
+        runId,
+      }).catch((error: unknown) => {
+        executorLog.warn(`${task.id}: failed to record workflow completion summary: ${error instanceof Error ? error.message : String(error)}`);
+      });
+    }
     const handedOff = await this.store.handoffToReview(task.id, {
       ownerAgentId: agentId ?? null,
       evidence: {
diff --git a/packages/engine/src/workflow-completion-summary.ts b/packages/engine/src/workflow-completion-summary.ts
new file mode 100644
index 0000000000..021d6b06ab
--- /dev/null
+++ b/packages/engine/src/workflow-completion-summary.ts
@@ -0,0 +1,73 @@
+import type { TaskDetail } from "@fusion/core";
+
+export interface WorkflowCompletionSummaryStore {
+  updateTask?: (taskId: string, updates: { summary: string }) => Promise<unknown> | unknown;
+  logEntry?: (taskId: string, action: string, detail?: string) => Promise<unknown> | unknown;
+}
+
+export interface WorkflowCompletionSummaryInput {
+  reason: string;
+  workflowId?: string;
+  runId?: string;
+}
+
+function truncateList(values: string[], limit: number): string {
+  const head = values.slice(0, limit);
+  const remaining = values.length - head.length;
+  return remaining > 0 ? `${head.join(", ")} and ${remaining} more` : head.join(", ");
+}
+
+export function buildWorkflowCompletionSummary(
+  task: Pick<TaskDetail, "id" | "title" | "steps" | "modifiedFiles" | "workflowStepResults">,
+  input: WorkflowCompletionSummaryInput,
+): string {
+  const title = task.title?.trim() || task.id;
+  const steps = task.steps ?? [];
+  const doneSteps = steps.filter((step) => step.status === "done" || step.status === "skipped").length;
+  const workflowResults = task.workflowStepResults ?? [];
+  const passedWorkflowSteps = workflowResults.filter((step) => step.status === "passed" || step.status === "skipped").length;
+  const files = (task.modifiedFiles ?? []).filter((file) => file.trim().length > 0);
+
+  const parts = [`Workflow completed: ${title}.`];
+  if (steps.length > 0) {
+    parts.push(`Completed ${doneSteps}/${steps.length} task step${steps.length === 1 ? "" : "s"}.`);
+  }
+  if (workflowResults.length > 0) {
+    parts.push(`Recorded ${passedWorkflowSteps}/${workflowResults.length} workflow check${workflowResults.length === 1 ? "" : "s"} as passed or skipped.`);
+  }
+  if (files.length > 0) {
+    parts.push(`Changed files: ${truncateList(files, 6)}.`);
+  }
+  parts.push(`Completion source: ${input.reason}${input.workflowId ? ` (${input.workflowId})` : ""}.`);
+  return parts.join(" ");
+}
+
+export async function ensureWorkflowCompletionSummary(
+  store: WorkflowCompletionSummaryStore,
+  task: TaskDetail,
+  input: WorkflowCompletionSummaryInput,
+): Promise<void> {
+  if (task.summary?.trim()) return;
+  if (!store.updateTask) return;
+
+  /*
+   * FNXC:WorkflowCompletion 2026-06-29-10:58:
+   * Workflow-owned tasks can finish through graph nodes and resumable merge work
+   * items without an agent calling `fn_task_done`. Persist a deterministic
+   * completion summary at the workflow lifecycle boundary so Done/Review cards,
+   * GitHub tracking, evals, and archival views see the same `task.summary`
+   * contract as legacy executor completions. Existing agent-authored summaries
+   * remain authoritative.
+   */
+  const summary = buildWorkflowCompletionSummary(task, input);
+  await store.updateTask(task.id, { summary });
+  await store.logEntry?.(
+    task.id,
+    "Workflow completion summary recorded",
+    JSON.stringify({
+      reason: input.reason,
+      workflowId: input.workflowId,
+      runId: input.runId,
+    }),
+  );
+}
diff --git a/packages/engine/src/workflow-task-runtime.ts b/packages/engine/src/workflow-task-runtime.ts
index 6f81994521..26cdb74925 100644
--- a/packages/engine/src/workflow-task-runtime.ts
+++ b/packages/engine/src/workflow-task-runtime.ts
@@ -20,6 +20,7 @@ import {
   type WorkflowCustomNodeRunner,
 } from "./workflow-node-handlers.js";
 import type { WorkflowRuntimePrimitives } from "./runtime-primitives.js";
+import { ensureWorkflowCompletionSummary } from "./workflow-completion-summary.js";
 
 export type WorkflowTaskRuntimeDisposition = "completed" | "failed" | "manual-required";
 
@@ -35,6 +36,8 @@ export interface WorkflowTaskRuntimeDeps extends Omit<WorkflowGraphExecutorDeps,
   store: WorkflowIrResolverStore & {
     getTask?: (taskId: string) => Promise<TaskDetail>;
     getTaskDocument?: (taskId: string, key: string) => Promise<unknown | null>;
+    updateTask?: (taskId: string, updates: { summary: string }) => Promise<unknown> | unknown;
+    logEntry?: (taskId: string, action: string, detail?: string) => Promise<unknown> | unknown;
     transitionWorkflowWorkItem?: (
       id: string,
       state: WorkflowWorkItemState,
@@ -130,6 +133,12 @@ export class WorkflowTaskRuntime {
           reason,
         };
       }
+      const latestTask = await this.deps.store.getTask?.(task.id).catch(() => undefined);
+      await ensureWorkflowCompletionSummary(this.deps.store, latestTask ?? task, {
+        reason: "workflow-runtime-completed",
+        workflowId: target.workflowId,
+        runId: this.deps.runId ?? `${task.id}:${target.workflowId}`,
+      }).catch(() => undefined);
     }
 
     const disposition: WorkflowTaskRuntimeDisposition = result.outcome === "success" ? "completed" : "failed";
@@ -180,6 +189,14 @@ export class WorkflowTaskRuntime {
       return this.failWorkItem(workItem, `workflow-work-item-node-missing:${workItem.nodeId}`);
     }
 
+    if (workItem.kind === "merge" || workItem.kind === "manual-hold") {
+      await ensureWorkflowCompletionSummary(this.deps.store, task, {
+        reason: `workflow-work-item:${workItem.kind}`,
+        workflowId: target.workflowId,
+        runId: workItem.runId,
+      }).catch(() => undefined);
+    }
+
     const invoked: string[] = [];
     const handler = this.recordingHandlers(invoked)[node.kind];
     if (!handler && node.kind !== "start" && node.kind !== "end") {