diff --git a/server/src/__tests__/agent-live-run-routes.test.ts b/server/src/__tests__/agent-live-run-routes.test.ts
index f902d888c03..493f68a984f 100644
--- a/server/src/__tests__/agent-live-run-routes.test.ts
+++ b/server/src/__tests__/agent-live-run-routes.test.ts
@@ -653,6 +653,48 @@ describe("agent live run routes", () => {
     });
   });
 
+  it.each([
+    ["was never written", async () => { throw Object.assign(Error("missing"), { name: "NoSuchKey" }); }, 404],
+    ["cannot be read from storage", async () => { throw Error("storage offline"); }, 500],
+  ] as const)("answers an object run log that %s", async (_case, getObject, status) => {
+    const { createObjectRunLogStore } = await vi.importActual<typeof import("../services/object-run-log-store.js")>("../services/object-run-log-store.js");
+    const store = createObjectRunLogStore({
+      provider: {
+        id: "s3",
+        getObject,
+        putObject: async () => { throw Error("unused"); },
+        putObjectConditional: async () => { throw Error("unused"); },
+        headObject: async () => ({ exists: false }),
+        deleteObject: async () => undefined,
+        listObjects: async () => ({ keys: [] }),
+      },
+      keyPrefix: "logs",
+      assertWriterAuthority: async () => undefined,
+    });
+    const handle = { store: "s3_segments" as const, logRef: "company-1/agent-1/aaaaaaaa-aaaa-4aaa-8aaa-aaaaaaaaaaaa" };
+    mockHeartbeatService.getRunLogAccess.mockResolvedValue({
+      id: "aaaaaaaa-aaaa-4aaa-8aaa-aaaaaaaaaaaa", companyId: "company-1", scopeKind: "company", issueId: null,
+      logStore: handle.store, logRef: handle.logRef,
+    });
+    mockHeartbeatService.readLog.mockImplementation(async () => store.read(handle));
+
+    const res = await requestApp(await createApp(), (baseUrl) =>
+      request(baseUrl).get("/api/heartbeat-runs/aaaaaaaa-aaaa-4aaa-8aaa-aaaaaaaaaaaa/log"),
+    );
+
+    expect(res.status, JSON.stringify(res.body)).toBe(status);
+    if (status === 404) expect(res.body).toEqual({ error: "Run log not found" });
+  });
+
+  it("does not read an object run log for another company", async () => {
+    const res = await requestApp(await createApp({}, {
+      type: "board", userId: "board-user", companyIds: ["company-2"], source: "session", isInstanceAdmin: false,
+    }), (baseUrl) => request(baseUrl).get("/api/heartbeat-runs/aaaaaaaa-aaaa-4aaa-8aaa-aaaaaaaaaaaa/log"));
+
+    expect(res.status).toBe(404);
+    expect(mockHeartbeatService.readLog).not.toHaveBeenCalled();
+  });
+
   it.each(["skill_test", "task_bridge"])(
     "denies %s keys from company-wide run and workspace logs",
     async (kind) => {
diff --git a/server/src/services/object-run-log-store.test.ts b/server/src/services/object-run-log-store.test.ts
index 2a637780194..04ccc8b2f50 100644
--- a/server/src/services/object-run-log-store.test.ts
+++ b/server/src/services/object-run-log-store.test.ts
@@ -321,7 +321,7 @@ describe("S3 run log store", () => {
     const m = memory(),
       store = createObjectRunLogStore({ provider: m.provider, keyPrefix: "logs", assertWriterAuthority: async () => undefined });
     await expect(store.read({ store: "s3_segments", logRef: "company/agent/never-written", attemptId: "attempt" }))
-      .rejects.toThrow("Object run log not found");
+      .rejects.toMatchObject({ status: 404, message: "Run log not found" });
   });
   it("batches concurrent appends, confirms durability, and resumes offsets/sequence on a replacement", async () => {
     const m = memory(),
diff --git a/server/src/services/object-run-log-store.ts b/server/src/services/object-run-log-store.ts
index 1065d61d6aa..154c996d320 100644
--- a/server/src/services/object-run-log-store.ts
+++ b/server/src/services/object-run-log-store.ts
@@ -4,6 +4,7 @@ import type { StorageProvider } from "../storage/types.js";
 import type { RunLogStore, RunLogHandle, RunLogBeginInput } from "./run-log-store.js";
 import { createObjectByteJournal, ObjectJournalSourcePrefixProofUnavailableError, type ObjectJournalIOPriority, type ObjectJournalWriter } from "./object-byte-journal.js";
 import { MAX_RUN_LOG_RECORD_BYTES } from "./run-log-record-limits.js";
+import { notFound } from "../errors.js";
 
 const MAX_SEGMENT_BYTES = 1024 * 1024;
 const MAX_PENDING_BYTES = MAX_RUN_LOG_RECORD_BYTES;
@@ -357,7 +358,7 @@ export function createObjectRunLogStore(options: ObjectRunLogStoreOptions): RunL
       if (handle.store !== "s3_segments" && handle.store !== "s3_archive") throw new Error("Invalid object run log backend");
       const store = journal(handle.logRef, opts.priority ?? "interactive"),
         snapshot = await store.head(opts.signal) ?? writers.get(handle)?.writer;
-      if (!snapshot || snapshot.head.deleted) throw new Error("Object run log not found");
+      if (!snapshot || snapshot.head.deleted) throw notFound("Run log not found");
       const offset = Math.max(0, opts.offset ?? 0),
         limit = opts.limitBytes ?? 256_000;
       if (!Number.isSafeInteger(limit) || limit < 1 || limit > MAX_READ_BYTES)