diff --git a/docs/3_TAKEAWAYS.md b/docs/3_TAKEAWAYS.md
index b831dbe..0d412db 100644
--- a/docs/3_TAKEAWAYS.md
+++ b/docs/3_TAKEAWAYS.md
@@ -192,7 +192,9 @@ Implementation: [`src/runner/protocol.ts`](../src/runner/protocol.ts) and
 A live exec stream can drop while the process continues. The in-Sandbox
 script therefore writes structured events and exit status to root-owned files.
 The host can poll for completion and download those files even after losing
-the stream.
+the stream. Once the script has exited, its output is required: the host
+retries the download in the same Sandbox rather than treating a failed
+download as an empty run, which would discard a paid investigation.
 
 Apply deadlines at several layers:
 
diff --git a/src/sandbox/render/sandbox.ts b/src/sandbox/render/sandbox.ts
index d82b8ca..5a3f63a 100644
--- a/src/sandbox/render/sandbox.ts
+++ b/src/sandbox/render/sandbox.ts
@@ -182,7 +182,11 @@ export async function runInvestigation(client: SandboxClient, id: string, opts:
   // A dropped exec stream doesn't stop the run, and the API can't reattach to it, so wait for the exit
   // status run-investigation.sh writes to a file instead.
   if (exitCode === null && !signal.aborted) exitCode = await awaitExitFile(client, id, runDir, signal);
-  const output = await readRunFile(client, id, `${runDir}.jsonl`, AbortSignal.timeout(client.t.verifyTimeoutMs));
+  // Once the script has exited, its output file exists: a failed download is an infrastructure error, not an empty run.
+  const outputSignal = AbortSignal.timeout(client.t.verifyTimeoutMs);
+  const output = exitCode === null
+    ? await readRunFile(client, id, `${runDir}.jsonl`, outputSignal)
+    : await readRunOutput(client, id, `${runDir}.jsonl`, outputSignal);
   return {
     exitCode,
     aborted: exitCode === null && signal.aborted,
@@ -192,6 +196,22 @@ export async function runInvestigation(client: SandboxClient, id: string, opts:
   };
 }
 
+const OUTPUT_DOWNLOAD_ATTEMPTS = 3;
+
+/** Retries in the same Sandbox, so a transport error doesn't repeat the model run. */
+async function readRunOutput(client: SandboxClient, id: string, path: string, signal: AbortSignal): Promise<string> {
+  for (let attempt = 1; ; attempt++) {
+    try {
+      return await client.download(id, path, signal);
+    } catch (err) {
+      if (attempt === OUTPUT_DOWNLOAD_ATTEMPTS || signal.aborted) {
+        throw new Error(`could not download ${path} from ${id} after ${attempt} attempt(s)`, { cause: err });
+      }
+      await sleep(client.t.pollMs, undefined, { signal }).catch(() => {});
+    }
+  }
+}
+
 /** Polls for the run's exit status until it appears, the sandbox stops running, or `signal` fires. */
 async function awaitExitFile(client: SandboxClient, id: string, runDir: string, signal: AbortSignal): Promise<number | null> {
   while (!signal.aborted) {
diff --git a/test/sandbox-render.test.ts b/test/sandbox-render.test.ts
index 350b6c8..ff4d59d 100644
--- a/test/sandbox-render.test.ts
+++ b/test/sandbox-render.test.ts
@@ -12,6 +12,7 @@ import { openRenderSandbox, runInvestigation } from "../src/sandbox/render/sandb
 import { buildSnapshot, pruneSnapshots } from "../src/sandbox/render/snapshot.ts";
 import { runnerInput } from "./helpers.ts";
 import { createLog } from "../src/log.ts";
+import { captureRun, classifyRun } from "../src/tasks.ts";
 
 const GH_TOKEN = "ghp_renderProviderSecret000000000000";
 const MODEL_KEY = "sk-ant-api03-renderProviderSecret";
@@ -428,6 +429,79 @@ const runsInvestigation = (events: () => SandboxExecEvent[] | AsyncGenerator<San
   (_id, command) => (command.includes("run-investigation.sh") ? events() : [exit(0)]);
 
 describe("runInvestigation", () => {
+  it("recovers required output after a transport failure without rerunning the investigation", async () => {
+    fake.exec_ = runsInvestigation(() => [exit(0)]);
+    let downloads = 0;
+    fake.file_ = (path) => {
+      if (!path.endsWith(".jsonl")) return undefined;
+      if (++downloads === 1) throw new TypeError("synthetic output transport failure");
+      return clarify;
+    };
+
+    const res = await runInvestigation(client(), "sbx-run", { input: runnerInput(LAYOUT), modelApiKey: MODEL_KEY, timeoutMs: 60_000 });
+
+    expect(res.events).toEqual([JSON.parse(clarify)]);
+    expect(classifyRun(res, captureRun(res.events), { elapsedMs: 1, agentTimeoutMs: 60_000 }).kind).toBe("result");
+    expect(downloads).toBe(2);
+    expect(fake.commands().filter((command) => command.includes("run-investigation.sh"))).toHaveLength(1);
+    expect(fake.calls.filter((call) => call.op === "upload" && call.path.endsWith("/key"))).toHaveLength(1);
+  });
+
+  it("throws an infrastructure error with the last transport cause after three output requests", async () => {
+    fake.exec_ = runsInvestigation(() => [exit(0)]);
+    const failures = [1, 2, 3].map((attempt) => new TypeError(`synthetic output failure ${attempt}`));
+    let downloads = 0;
+    fake.file_ = (path) => {
+      if (!path.endsWith(".jsonl")) return undefined;
+      throw failures[downloads++];
+    };
+
+    const error = await runInvestigation(client(), "sbx-run", { input: runnerInput(LAYOUT), timeoutMs: 60_000 }).catch((err: unknown) => err);
+
+    expect(error).toMatchObject({ message: expect.stringContaining("after 3 attempt(s)"), cause: failures[2] });
+    expect(downloads).toBe(3);
+    expect(fake.commands().filter((command) => command.includes("run-investigation.sh"))).toHaveLength(1);
+  });
+
+  it("keeps a genuinely downloaded empty output as an agent failure, without transport retries", async () => {
+    fake.exec_ = runsInvestigation(() => [exit(0)]);
+    let downloads = 0;
+    fake.file_ = (path) => path.endsWith(".jsonl") ? (downloads++, "") : undefined;
+
+    const res = await runInvestigation(client(), "sbx-run", { input: runnerInput(LAYOUT), timeoutMs: 60_000 });
+
+    expect(res).toMatchObject({ exitCode: 0, aborted: false, events: [], invalidLines: 0 });
+    expect(classifyRun(res, captureRun(res.events), { elapsedMs: 1, agentTimeoutMs: 60_000 })).toMatchObject({ kind: "failed", code: "agent_error" });
+    expect(downloads).toBe(1);
+  });
+
+  it("keeps an aborted run's output best-effort", async () => {
+    const controller = new AbortController();
+    fake.exec_ = runsInvestigation(async function* () {
+      controller.abort();
+      throw new AbortError();
+    });
+
+    const res = await runInvestigation(client(), "sbx-run", { input: runnerInput(LAYOUT), timeoutMs: 60_000, signal: controller.signal });
+
+    expect(res).toMatchObject({ exitCode: null, aborted: true, events: [] });
+    expect(classifyRun(res, captureRun(res.events), { elapsedMs: 1, agentTimeoutMs: 60_000 })).toMatchObject({ kind: "failed", code: "timeout" });
+  });
+
+  it("recovers a complete result even after an explicit abort", async () => {
+    const controller = new AbortController();
+    fake.exec_ = runsInvestigation(async function* () {
+      controller.abort();
+      throw new AbortError();
+    });
+    fake.file_ = (path) => path.endsWith(".jsonl") ? clarify : undefined;
+
+    const res = await runInvestigation(client(), "sbx-run", { input: runnerInput(LAYOUT), timeoutMs: 60_000, signal: controller.signal });
+
+    expect(res.aborted).toBe(true);
+    expect(classifyRun(res, captureRun(res.events), { elapsedMs: 1, agentTimeoutMs: 60_000 }).kind).toBe("result");
+  });
+
   it("returns the run's events and exit status, streaming stderr and counting invalid lines", async () => {
     const started = event({ type: "started", pi_version: "0.83.0", model: "m", prompt_version: "v3" });
     fake.exec_ = runsInvestigation(() => [out("runner ", "stderr"), out("diagnostics", "stderr"), exit(0)]);
@@ -442,6 +516,7 @@ describe("runInvestigation", () => {
   });
 
   it("uploads the model key as a file beside the input and never puts it in a command", async () => {
+    fake.file_ = (path) => path.endsWith(".jsonl") ? "" : undefined;
     await runInvestigation(client(), "sbx-run", { input: runnerInput(LAYOUT), modelApiKey: MODEL_KEY, timeoutMs: 90_000 });
 
     expect(fake.commands().some((c) => c.includes(MODEL_KEY))).toBe(false);