diff --git a/wasm/app/worker.mjs b/wasm/app/worker.mjs
index a5f39b7..cae8b53 100644
--- a/wasm/app/worker.mjs
+++ b/wasm/app/worker.mjs
@@ -55,13 +55,22 @@ self.onmessage = async (e) => {
     // calls.
     const CHUNK_FLUSH_BYTES = 65536;
     const CHUNK_FLUSH_NEWLINES = 4096;
+    // Wall-clock flush — guarantees the first emission lands on the UI
+    // immediately and caps low-rate streams at ~10 flushes/sec. Without
+    // this, a (let loop ...) that emits every 10K iterations would
+    // accumulate 30 bytes per emit, take 2000+ emits to hit the 64KB
+    // threshold, and the user sees nothing for seconds. lastFlushTime
+    // starts at 0 so the first chunk to land always triggers a flush.
+    const FLUSH_INTERVAL_MS = 100;
     let chunkBuffer = "";
     let chunkNewlines = 0;
+    let lastFlushTime = 0;
     function flushChunkBuffer() {
         if (!chunkBuffer) return;
         self.postMessage({ kind: "chunk-batch", runId, tier, text: chunkBuffer });
         chunkBuffer = "";
         chunkNewlines = 0;
+        lastFlushTime = Date.now();
     }
     try {
         const output = await evalOnTier(
@@ -77,7 +86,8 @@ self.onmessage = async (e) => {
                     if (chunk.charCodeAt(i) === 10) chunkNewlines++;
                 }
                 if (chunkBuffer.length >= CHUNK_FLUSH_BYTES
-                    || chunkNewlines >= CHUNK_FLUSH_NEWLINES) {
+                    || chunkNewlines >= CHUNK_FLUSH_NEWLINES
+                    || (Date.now() - lastFlushTime) >= FLUSH_INTERVAL_MS) {
                     flushChunkBuffer();
                 }
             },
diff --git a/wasm/dist-repl/worker.mjs b/wasm/dist-repl/worker.mjs
index a5f39b7..cae8b53 100644
--- a/wasm/dist-repl/worker.mjs
+++ b/wasm/dist-repl/worker.mjs
@@ -55,13 +55,22 @@ self.onmessage = async (e) => {
     // calls.
     const CHUNK_FLUSH_BYTES = 65536;
     const CHUNK_FLUSH_NEWLINES = 4096;
+    // Wall-clock flush — guarantees the first emission lands on the UI
+    // immediately and caps low-rate streams at ~10 flushes/sec. Without
+    // this, a (let loop ...) that emits every 10K iterations would
+    // accumulate 30 bytes per emit, take 2000+ emits to hit the 64KB
+    // threshold, and the user sees nothing for seconds. lastFlushTime
+    // starts at 0 so the first chunk to land always triggers a flush.
+    const FLUSH_INTERVAL_MS = 100;
     let chunkBuffer = "";
     let chunkNewlines = 0;
+    let lastFlushTime = 0;
     function flushChunkBuffer() {
         if (!chunkBuffer) return;
         self.postMessage({ kind: "chunk-batch", runId, tier, text: chunkBuffer });
         chunkBuffer = "";
         chunkNewlines = 0;
+        lastFlushTime = Date.now();
     }
     try {
         const output = await evalOnTier(
@@ -77,7 +86,8 @@ self.onmessage = async (e) => {
                     if (chunk.charCodeAt(i) === 10) chunkNewlines++;
                 }
                 if (chunkBuffer.length >= CHUNK_FLUSH_BYTES
-                    || chunkNewlines >= CHUNK_FLUSH_NEWLINES) {
+                    || chunkNewlines >= CHUNK_FLUSH_NEWLINES
+                    || (Date.now() - lastFlushTime) >= FLUSH_INTERVAL_MS) {
                     flushChunkBuffer();
                 }
             },
diff --git a/www/playground/worker.mjs b/www/playground/worker.mjs
index a5f39b7..cae8b53 100644
--- a/www/playground/worker.mjs
+++ b/www/playground/worker.mjs
@@ -55,13 +55,22 @@ self.onmessage = async (e) => {
     // calls.
     const CHUNK_FLUSH_BYTES = 65536;
     const CHUNK_FLUSH_NEWLINES = 4096;
+    // Wall-clock flush — guarantees the first emission lands on the UI
+    // immediately and caps low-rate streams at ~10 flushes/sec. Without
+    // this, a (let loop ...) that emits every 10K iterations would
+    // accumulate 30 bytes per emit, take 2000+ emits to hit the 64KB
+    // threshold, and the user sees nothing for seconds. lastFlushTime
+    // starts at 0 so the first chunk to land always triggers a flush.
+    const FLUSH_INTERVAL_MS = 100;
     let chunkBuffer = "";
     let chunkNewlines = 0;
+    let lastFlushTime = 0;
     function flushChunkBuffer() {
         if (!chunkBuffer) return;
         self.postMessage({ kind: "chunk-batch", runId, tier, text: chunkBuffer });
         chunkBuffer = "";
         chunkNewlines = 0;
+        lastFlushTime = Date.now();
     }
     try {
         const output = await evalOnTier(
@@ -77,7 +86,8 @@ self.onmessage = async (e) => {
                     if (chunk.charCodeAt(i) === 10) chunkNewlines++;
                 }
                 if (chunkBuffer.length >= CHUNK_FLUSH_BYTES
-                    || chunkNewlines >= CHUNK_FLUSH_NEWLINES) {
+                    || chunkNewlines >= CHUNK_FLUSH_NEWLINES
+                    || (Date.now() - lastFlushTime) >= FLUSH_INTERVAL_MS) {
                     flushChunkBuffer();
                 }
             },
diff --git a/www/repl/worker.mjs b/www/repl/worker.mjs
index a5f39b7..cae8b53 100644
--- a/www/repl/worker.mjs
+++ b/www/repl/worker.mjs
@@ -55,13 +55,22 @@ self.onmessage = async (e) => {
     // calls.
     const CHUNK_FLUSH_BYTES = 65536;
     const CHUNK_FLUSH_NEWLINES = 4096;
+    // Wall-clock flush — guarantees the first emission lands on the UI
+    // immediately and caps low-rate streams at ~10 flushes/sec. Without
+    // this, a (let loop ...) that emits every 10K iterations would
+    // accumulate 30 bytes per emit, take 2000+ emits to hit the 64KB
+    // threshold, and the user sees nothing for seconds. lastFlushTime
+    // starts at 0 so the first chunk to land always triggers a flush.
+    const FLUSH_INTERVAL_MS = 100;
     let chunkBuffer = "";
     let chunkNewlines = 0;
+    let lastFlushTime = 0;
     function flushChunkBuffer() {
         if (!chunkBuffer) return;
         self.postMessage({ kind: "chunk-batch", runId, tier, text: chunkBuffer });
         chunkBuffer = "";
         chunkNewlines = 0;
+        lastFlushTime = Date.now();
     }
     try {
         const output = await evalOnTier(
@@ -77,7 +86,8 @@ self.onmessage = async (e) => {
                     if (chunk.charCodeAt(i) === 10) chunkNewlines++;
                 }
                 if (chunkBuffer.length >= CHUNK_FLUSH_BYTES
-                    || chunkNewlines >= CHUNK_FLUSH_NEWLINES) {
+                    || chunkNewlines >= CHUNK_FLUSH_NEWLINES
+                    || (Date.now() - lastFlushTime) >= FLUSH_INTERVAL_MS) {
                     flushChunkBuffer();
                 }
             },