Focus on speedup and not hanging on large audio files.

src/server/transcribe.ts

@@ -282,6 +282,19 @@ export function createSidecar(command?: readonly string[]): Sidecar {
 /** Default cap ≈ 2¼ hours of raw float32 16 kHz mono (64 kB/s). */
 const DEFAULT_MAX_UPLOAD_BYTES = 512 * 1024 * 1024;
 
+/**
+ * Effective upload cap (env-overridable). Exported so src/index.ts can raise
+ * Bun.serve's `maxRequestBodySize` to match — its 128 MB default would
+ * otherwise reject uploads longer than ~35 minutes of audio before this
+ * module ever sees them.
+ */
+export const MAX_UPLOAD_BYTES =
+  Number(process.env.TRANSCRIBE_MAX_UPLOAD_BYTES) || DEFAULT_MAX_UPLOAD_BYTES;
+
+/** Keep the ndjson stream visibly alive through quiet stretches (D-021). */
+const HEARTBEAT_INTERVAL_MS = 5_000;
+const HEARTBEAT = new TextEncoder().encode("\n");
+
 const LANGUAGE_RE = /^[a-z]{2,3}$/;
 
 export interface TranscribeHandlers {
@@ -410,6 +423,20 @@ export function createTranscribeHandlers(deps: TranscribeDeps): TranscribeHandle
         async start(controller) {
           const enqueue = (line: TranscribeStreamLine) =>
             controller.enqueue(encoder.encode(`${JSON.stringify(line)}\n`));
+          // Segment gaps can exceed any proxy/server idle timeout (model
+          // load/download before the first segment; slow decode windows on
+          // big models — 30 s+ observed on a 15-min file). Heartbeat blank
+          // lines keep the connection visibly alive; ServerEngine's line
+          // reader skips empty lines. A dead client makes the enqueue throw,
+          // which is caught here (request.signal separately cancels the
+          // sidecar pass).
+          const heartbeat = setInterval(() => {
+            try {
+              controller.enqueue(HEARTBEAT);
+            } catch {
+              clearInterval(heartbeat);
+            }
+          }, HEARTBEAT_INTERVAL_MS);
           const chunks: TranscriptChunk[] = [];
           try {
             await deps.sidecar.transcribe(
@@ -445,6 +472,7 @@ export function createTranscribeHandlers(deps: TranscribeDeps): TranscribeHandle
               message: error instanceof Error ? error.message : String(error),
             });
           } finally {
+            clearInterval(heartbeat);
             await Bun.file(audioPath).unlink().catch(() => {});
             try {
               controller.close();
@@ -475,5 +503,5 @@ export const sidecar = createSidecar();
 export const transcribe: TranscribeHandlers = createTranscribeHandlers({
   sidecar,
   getSessionUser: appGetSessionUser,
-  maxUploadBytes: Number(process.env.TRANSCRIBE_MAX_UPLOAD_BYTES) || undefined,
+  maxUploadBytes: MAX_UPLOAD_BYTES,
 });