fix(runner): keep a mid-body network cut as a transport error in fetchDocsJson (DEV-3370)

runner/apps/authoring/src/docs-catalog.ts

@@ -57,6 +57,9 @@ async function fetchDocsJson<T>(url: string, describe: string): Promise<T> {
     try {
       return (await res.json()) as T;
     } catch (cause) {
+      // A connection cut mid-body is a transport failure, not a bad artifact, so it
+      // keeps its own error rather than being reported as unparseable JSON.
+      if (!(cause instanceof SyntaxError)) throw cause;
       // A truncated or half-uploaded artifact served correctly as JSON. Left as a
       // plain (transient) Error — the host does have the file — but re-thrown with
       // `describe` so it still carries the bucket key. A bare `res.json()` reject

runner/pipeline/docs-catalog.test.mjs

@@ -170,6 +170,18 @@ test("manifest: a truncated body served as application/json names the bucket and
   assert.equal(error.cause instanceof Error, true);
 });
 
+test("manifest: a body stream cut by the network rethrows the transport error, not an unparseable-JSON one", async (t) => {
+  // The headers arrived as application/json but the connection died mid-body, so
+  // `res.json()` rejects with the browser's own `TypeError: Failed to fetch`.
+  const cut = new TypeError("Failed to fetch");
+  withFetch(t, () => ({ ...reply({ body: "" }), json: async () => { throw cut; } }));
+
+  const error = await rejection(fetchDocsManifest("net-cut"));
+
+  assert.equal(error, cut);
+  assert.equal(isDocsResourceMissing(error), false);
+});
+
 test("manifest: a 200 body that is neither HTML nor JSON rejects as non-missing", async (t) => {
   withFetch(t, () => reply({ contentType: "text/plain", body: "not json at all" }));