diff --git a/apps/mobile/src/host/text-playback.ts b/apps/mobile/src/host/text-playback.ts
index 62b3ce195f..400c1ba2b5 100644
--- a/apps/mobile/src/host/text-playback.ts
+++ b/apps/mobile/src/host/text-playback.ts
@@ -71,15 +71,10 @@ export function createTextPlayback(initial = '', now = Date.now()) {
       const oldLength = ends.length;
       const shown = body.length;
       const from = next.startsWith(target) ? (ends.at(-2) ?? 0) : 0;
-      const kept = from === 0 ? [] : ends.filter((end) => end <= from);
-      ends = [
-        ...kept,
-        ...[...graphemeSegments(next.slice(from))].map(
-          (part) => from + part.index + part.segment.length,
-        ),
-      ];
-      cursor = ends.findIndex((end) => end > shown);
-      if (cursor < 0) cursor = ends.length;
+      ends.length = from === 0 ? 0 : ends.length - 1;
+      for (const part of graphemeSegments(next.slice(from)))
+        ends.push(from + part.index + part.segment.length);
+      cursor = firstEndAfter(ends, shown);
       target = next;
       const added = Math.max(0, ends.length - oldLength);
       if (added > 0) {
@@ -159,4 +154,15 @@ export function createTextPlayback(initial = '', now = Date.now()) {
   };
 }
 
+function firstEndAfter(ends: number[], offset: number) {
+  let low = 0;
+  let high = ends.length;
+  while (low < high) {
+    const middle = (low + high) >>> 1;
+    if (ends[middle]! > offset) high = middle;
+    else low = middle + 1;
+  }
+  return low;
+}
+
 export type TextPlayback = ReturnType<typeof createTextPlayback>;
diff --git a/apps/mobile/src/ui/chat/message-bubble.tsx b/apps/mobile/src/ui/chat/message-bubble.tsx
index c9b24113f9..f6e67bdfb2 100644
--- a/apps/mobile/src/ui/chat/message-bubble.tsx
+++ b/apps/mobile/src/ui/chat/message-bubble.tsx
@@ -452,14 +452,14 @@ function PressableBubble({
     if (anchor.current !== undefined) onLongPress(anchor.current);
     else measure(onLongPress);
   };
-  const hold =
-    onLongPress === undefined
-      ? undefined
-      : () => {
-          haptic('menu');
-          if (shrinks) scale.value = withSpring(1, spring.spatial.fast);
-          open();
-        };
+  const holdRef = useRef<() => void>(undefined);
+  holdRef.current = () => {
+    haptic('menu');
+    if (shrinks) scale.value = withSpring(1, spring.spatial.fast);
+    open();
+  };
+  const holds = onLongPress !== undefined;
+  const hold = useMemo(() => (holds ? () => holdRef.current?.() : undefined), [holds]);
   return (
     <Animated.View
       ref={ref}
diff --git a/changes/ios-streaming-playback-scan.md b/changes/ios-streaming-playback-scan.md
new file mode 100644
index 0000000000..b374b10863
--- /dev/null
+++ b/changes/ios-streaming-playback-scan.md
@@ -0,0 +1,11 @@
+---
+section: Fixed
+---
+
+## en
+
+- Streaming a long reply no longer slows down as the reply grows: the text playback no longer rescans every earlier character on each update ([#3974](https://github.com/BotHarness/DeepSeekBot/issues/3974)).
+
+## zh
+
+- 流式输出长回复时不再越来越慢：文字播放不再在每次更新时重新扫描之前所有字符（[#3974](https://github.com/BotHarness/DeepSeekBot/issues/3974)）。
diff --git a/packages/core/src/devices/noise/channel.ts b/packages/core/src/devices/noise/channel.ts
index 795e241dea..960734e566 100644
--- a/packages/core/src/devices/noise/channel.ts
+++ b/packages/core/src/devices/noise/channel.ts
@@ -1,4 +1,4 @@
-import { bytesToHex, hexToBytes, concatBytes, utf8ToBytes } from '@noble/hashes/utils.js';
+import { bytesToHex, concatBytes, utf8ToBytes } from '@noble/hashes/utils.js';
 import { NoiseXk, NOISE_PROTOCOL, type NoiseTransport, type NoiseKeyAgreement } from './xk.js';
 
 export const CONNECT_PROTOCOL = 'connect-noise-xk-v1';
@@ -15,6 +15,20 @@ export interface ChannelResult {
   ready?: true;
 }
 
+const NIBBLE = new Int8Array(128).fill(-1);
+for (let index = 0; index < 16; index++) NIBBLE['0123456789abcdef'.charCodeAt(index)] = index;
+
+function wireBytes(wire: string): Uint8Array {
+  const bytes = new Uint8Array((wire.length - 1) / 2);
+  for (let index = 0, at = 1; index < bytes.length; index++, at += 2) {
+    const high = NIBBLE[wire.charCodeAt(at)] ?? -1;
+    const low = NIBBLE[wire.charCodeAt(at + 1)] ?? -1;
+    if (high < 0 || low < 0) throw new Error('channel-frame-invalid');
+    bytes[index] = (high << 4) | low;
+  }
+  return bytes;
+}
+
 export class ConnectChannel {
   private readonly noise: NoiseXk;
   private readonly role: 'initiator' | 'responder';
@@ -71,7 +85,8 @@ export class ConnectChannel {
       if (
         this.closed ||
         wire.length > 2 * (HEADER + CHUNK + 17) + 1 ||
-        !/^[hd][0-9a-f]+$/u.test(wire) ||
+        (wire[0] !== 'h' && wire[0] !== 'd') ||
+        wire.length < 3 ||
         wire.length % 2 !== 1
       )
         throw new Error('channel-frame-invalid');
@@ -83,8 +98,7 @@ export class ConnectChannel {
           (this.role === 'initiator' && this.stage !== 1)
         )
           throw new Error('channel-handshake-invalid');
-        if (this.noise.read(hexToBytes(wire.slice(1))).length !== 0)
-          throw new Error('channel-early-payload');
+        if (this.noise.read(wireBytes(wire)).length !== 0) throw new Error('channel-early-payload');
         if (this.role === 'responder' && this.stage === 0) {
           this.stage = 1;
           return { reply: `h${bytesToHex(this.noise.write())}` };
@@ -94,7 +108,7 @@ export class ConnectChannel {
         return { ...(reply === undefined ? {} : { reply }), ready: true };
       }
       if (wire[0] !== 'd') throw new Error('channel-frame-invalid');
-      const frame = hexToBytes(wire.slice(1));
+      const frame = wireBytes(wire);
       if (frame.length < HEADER + 17) throw new Error('channel-length-invalid');
       const header = frame.subarray(0, HEADER);
       const view = new DataView(header.buffer, header.byteOffset, header.byteLength);