diff --git a/.changeset/quiet-streams-order.md b/.changeset/quiet-streams-order.md
new file mode 100644
index 0000000000..cadb40cbae
--- /dev/null
+++ b/.changeset/quiet-streams-order.md
@@ -0,0 +1,5 @@
+---
+"@workflow/world-local": patch
+---
+
+Fix race condition in streamer when multiple writes share a promise runId.
diff --git a/packages/world-local/src/streamer.test.ts b/packages/world-local/src/streamer.test.ts
index 62f1a98c0c..6fb9fb1915 100644
--- a/packages/world-local/src/streamer.test.ts
+++ b/packages/world-local/src/streamer.test.ts
@@ -102,8 +102,10 @@ describe('streamer', () => {
             const chunk = deserializeChunk(
               await fs.readFile(`${testDir}/streams/chunks/${file}`)
             );
-            const stream_id = String(file.split('-').at(-1)).split('.')[0];
-            const time = decodeTime(stream_id);
+            // Extract ULID from filename: "streamName-chnk_ULID.json"
+            const chunkIdPart = String(file.split('-').at(-1)).split('.')[0]; // "chnk_ULID"
+            const ulid = chunkIdPart.replace('chnk_', ''); // Just the ULID
+            const time = decodeTime(ulid);
             const timeDiff = time - lastTime;
             lastTime = time;
 
diff --git a/packages/world-local/src/streamer.ts b/packages/world-local/src/streamer.ts
index b8380e4029..bf22112d68 100644
--- a/packages/world-local/src/streamer.ts
+++ b/packages/world-local/src/streamer.ts
@@ -93,14 +93,17 @@ export function createStreamer(basedir: string): Streamer {
       _runId: string | Promise<string>,
       chunk: string | Uint8Array
     ) {
+      // Generate ULID synchronously BEFORE any await to preserve call order.
+      // This ensures that chunks written in sequence maintain their order even
+      // when runId is a promise that multiple writes are waiting on.
+      const chunkId = `chnk_${monotonicUlid()}`;
+
       // Await runId if it's a promise to ensure proper flushing
       const runId = await _runId;
 
       // Register this stream for the run
       await registerStreamForRun(runId, name);
 
-      const chunkId = `chnk_${monotonicUlid()}`;
-
       // Convert chunk to buffer for serialization
       let chunkBuffer: Buffer;
       if (typeof chunk === 'string') {
@@ -136,13 +139,14 @@ export function createStreamer(basedir: string): Streamer {
     },
 
     async closeStream(name: string, _runId: string | Promise<string>) {
+      // Generate ULID synchronously BEFORE any await to preserve call order.
+      const chunkId = `chnk_${monotonicUlid()}`;
+
       // Await runId if it's a promise to ensure proper flushing
       const runId = await _runId;
 
       // Register this stream for the run (in case writeToStream wasn't called)
       await registerStreamForRun(runId, name);
-
-      const chunkId = `chnk_${monotonicUlid()}`;
       const chunkPath = path.join(
         basedir,
         'streams',