fix(agents): preserve fiber result when cleanup fails

.changeset/quiet-fibers-finish.md

@@ -0,0 +1,5 @@
+---
+"agents": patch
+---
+
+Preserve a legacy `runFiber` result when deleting its bookkeeping row fails. The cleanup error is logged and the row is left for the existing recovery pass instead of replacing the fiber body's outcome.

packages/agents/src/index.ts

@@ -4657,17 +4657,24 @@ export class Agent<
       }
     } finally {
       this._runFiberActiveFibers.delete(id);
-      this._withAgentSpan(
-        "finalize_fiber",
-        "fiber",
-        {
-          "cloudflare.agents.fiber.id": id,
-          "cloudflare.agents.fiber.name": name
-        },
-        () => {
-          this.sql`DELETE FROM cf_agents_runs WHERE id = ${id}`;
-        }
-      );
+      try {
+        this._withAgentSpan(
+          "finalize_fiber",
+          "fiber",
+          {
+            "cloudflare.agents.fiber.id": id,
+            "cloudflare.agents.fiber.name": name
+          },
+          () => {
+            this.sql`DELETE FROM cf_agents_runs WHERE id = ${id}`;
+          }
+        );
+      } catch (error) {
+        console.error(
+          `[Agent] Failed to finalize fiber "${name}" (${id}); leaving run row for recovery:`,
+          error
+        );
+      }
       dispose();
       if (root && registeredFacetRun) {
         try {

packages/agents/src/tests/agents/run-fiber.ts

@@ -57,6 +57,23 @@ export class TestRunFiberAgent extends Agent {
     });
   }
 
+  async runWithFailingCleanup(value: string): Promise<string> {
+    this.sql`
+      CREATE TRIGGER fail_run_fiber_cleanup
+      BEFORE DELETE ON cf_agents_runs
+      WHEN OLD.name = 'cleanup-failure'
+      BEGIN
+        SELECT RAISE(FAIL, 'simulated fiber cleanup failure');
+      END
+    `;
+
+    try {
+      return await this.runFiber("cleanup-failure", async () => value);
+    } finally {
+      this.sql`DROP TRIGGER fail_run_fiber_cleanup`;
+    }
+  }
+
   async runWithCheckpoint(steps: string[]): Promise<string[]> {
     return this.runFiber("checkpoint", async (ctx) => {
       const completed: string[] = [];

packages/agents/src/tests/run-fiber.test.ts

@@ -48,6 +48,21 @@ describe("runFiber", () => {
       expect(log).toContain("executed:hello");
     });
 
+    it("preserves a successful result when fiber cleanup fails", async () => {
+      const agent = await getAgentByName(
+        env.TestRunFiberAgent,
+        "run-cleanup-failure"
+      );
+
+      await expect(agent.runWithFailingCleanup("completed")).resolves.toBe(
+        "completed"
+      );
+      expect((await agent.getRunningFiberCount()) as unknown as number).toBe(1);
+
+      await agent.triggerRecoveryCheck();
+      expect((await agent.getRunningFiberCount()) as unknown as number).toBe(0);
+    });
+
     it("should delete the fiber row on completion", async () => {
       const agent = await getAgentByName(env.TestRunFiberAgent, "run-cleanup");