fix(server): release a refused download's body before reporting it

CHANGELOG.md

@@ -8,6 +8,10 @@ Newest first. `Unreleased` is what is on `main` and not yet tagged.
 
 ## Unreleased
 
+- A file download refused because the computer's response carried no usable byte length now releases
+  the connection before reporting the refusal. The unread body could be as large as the whole
+  download budget, so a computer reached through a proxy that re-chunks left a transfer running and a
+  connection checked out of the pool on every attempt.
 ### A Bot's turn in a group is no longer offered coordination tools it cannot call
 
 A Bot answering another Bot in a group conversation was offered `ask_person`, and `message_bot`

server/src/computer/client.ts

@@ -293,6 +293,10 @@ export function createComputerTransport(
     const bytes =
       length !== null && /^\d+$/.test(length) ? Number(length) : Number.NaN;
     if (!response.body || !Number.isSafeInteger(bytes) || bytes < 0) {
+      // Nothing else will ever read this body, so release it here rather than
+      // leaving the whole download budget checked out of the pool. A cancel that
+      // fails must not replace the refusal the caller is told about.
+      await response.body?.cancel().catch(() => undefined);
       throw new ComputerUnavailableError(
         "The assistant's computer returned an invalid file download.",
       );

server/tests/computer-client.test.ts

@@ -73,6 +73,40 @@ describe("computer client", () => {
       );
     });
 
+    test("releases the connection it refuses to hand back", async () => {
+      let cancelled = false;
+      const body = new ReadableStream<Uint8Array>({
+        start(controller) {
+          controller.enqueue(Uint8Array.from([1, 2, 3]));
+        },
+        cancel() {
+          cancelled = true;
+        },
+      });
+      const client = clientWith(() => new Response(body));
+
+      await expect(client.download("x")).rejects.toThrow(
+        ComputerUnavailableError,
+      );
+      expect(cancelled).toBe(true);
+    });
+
+    test("still names the invalid download when releasing it fails", async () => {
+      const body = new ReadableStream<Uint8Array>({
+        start(controller) {
+          controller.enqueue(Uint8Array.from([1, 2, 3]));
+        },
+        cancel() {
+          throw new Error("socket already gone");
+        },
+      });
+      const client = clientWith(() => new Response(body));
+
+      await expect(client.download("x")).rejects.toThrow(
+        ComputerUnavailableError,
+      );
+    });
+
     test.each([
       [404, WorkspaceNotFoundError],
       [413, WorkspaceTooLargeError],