diff --git a/server/src/__tests__/agent-auth-middleware.test.ts b/server/src/__tests__/agent-auth-middleware.test.ts
index 23cb8e06fa..9adc3003fb 100644
--- a/server/src/__tests__/agent-auth-middleware.test.ts
+++ b/server/src/__tests__/agent-auth-middleware.test.ts
@@ -372,6 +372,38 @@ describe("agent auth middleware", () => {
     });
   });
 
+  it("audits a run header mismatch even when the claimed run does not exist", async () => {
+    const companyId = randomUUID();
+    const agentId = randomUUID();
+    const claimedRunId = randomUUID();
+    const spoofedRunId = randomUUID();
+    const { db, activity } = createDbState({
+      agent: { id: agentId, companyId },
+    });
+    const token = createLocalAgentJwt(agentId, companyId, "codex_local", claimedRunId, "user-claim");
+
+    const res = await request(createApp(db))
+      .get("/actor")
+      .set("Authorization", `Bearer ${token}`)
+      .set("X-Paperclip-Run-Id", spoofedRunId);
+
+    expect(res.status).toBe(422);
+    expect(res.body.code).toBe("agent_jwt_run_id_mismatch");
+    expect(activity).toHaveLength(1);
+    expect(activity[0]).toMatchObject({
+      companyId,
+      actorType: "agent",
+      actorId: agentId,
+      action: "auth.agent_jwt_run_header_mismatch",
+      entityType: "heartbeat_run",
+      entityId: claimedRunId,
+      details: { claimRunId: claimedRunId, headerRunId: spoofedRunId },
+    });
+    // run_id carries a real FK to heartbeat_runs; a nonexistent claim must not
+    // be written into it or the whole audit row is lost to the FK violation.
+    expect(activity[0].runId).toBeUndefined();
+  });
+
   it("falls back to the run row responsible user for legacy claim-less agent JWTs", async () => {
     const companyId = randomUUID();
     const agentId = randomUUID();
diff --git a/server/src/middleware/auth.ts b/server/src/middleware/auth.ts
index 8de3f1c171..f636d57fbc 100644
--- a/server/src/middleware/auth.ts
+++ b/server/src/middleware/auth.ts
@@ -157,6 +157,18 @@ async function auditAgentJwtRunHeaderMismatch(
   input: { companyId: string; agentId: string; claimRunId: string; headerRunId: string; method: string; url: string },
 ) {
   try {
+    // The claimed run id is untrusted input from a rejected token. activity_log
+    // .run_id is a real FK to heartbeat_runs, so writing it unconditionally
+    // makes the insert fail — and the catch swallows it — exactly when the
+    // claim is bogus. Keep the claim in entityId/details and populate the FK
+    // column only when the row actually exists.
+    const claimedRunExists = isUuidLike(input.claimRunId)
+      ? await db
+          .select({ id: heartbeatRuns.id })
+          .from(heartbeatRuns)
+          .where(eq(heartbeatRuns.id, input.claimRunId))
+          .then((rows) => rows.length > 0)
+      : false;
     await db.insert(activityLog).values({
       companyId: input.companyId,
       actorType: "agent",
@@ -165,7 +177,7 @@ async function auditAgentJwtRunHeaderMismatch(
       entityType: "heartbeat_run",
       entityId: input.claimRunId,
       ...(isUuidLike(input.agentId) ? { agentId: input.agentId } : {}),
-      ...(isUuidLike(input.claimRunId) ? { runId: input.claimRunId } : {}),
+      ...(claimedRunExists ? { runId: input.claimRunId } : {}),
       details: {
         claimRunId: input.claimRunId,
         headerRunId: input.headerRunId,