fix: avoid invalid UTF-16 in truncation (#567)

src/agents/bash-tools.ts

@@ -8,6 +8,7 @@ import type { AgentTool, AgentToolResult } from "@mariozechner/pi-agent-core";
 import { Type } from "@sinclair/typebox";
 
 import { logInfo } from "../logger.js";
+import { sliceUtf16Safe } from "../utils.js";
 import {
   addSession,
   appendOutput,
@@ -1041,7 +1042,7 @@ function chunkString(input: string, limit = CHUNK_LIMIT) {
 function truncateMiddle(str: string, max: number) {
   if (str.length <= max) return str;
   const half = Math.floor((max - 3) / 2);
-  return `${str.slice(0, half)}...${str.slice(str.length - half)}`;
+  return `${sliceUtf16Safe(str, 0, half)}...${sliceUtf16Safe(str, -half)}`;
 }
 
 function sliceLogLines(

src/agents/pi-embedded-subscribe.ts

@@ -9,6 +9,7 @@ import { resolveStateDir } from "../config/paths.js";
 import { emitAgentEvent } from "../infra/agent-events.js";
 import { createSubsystemLogger } from "../logging.js";
 import { splitMediaFromOutput } from "../media/parse.js";
+import { truncateUtf16Safe } from "../utils.js";
 import type { BlockReplyChunking } from "./pi-embedded-block-chunker.js";
 import { EmbeddedBlockChunker } from "./pi-embedded-block-chunker.js";
 import { isMessagingToolDuplicate } from "./pi-embedded-helpers.js";
@@ -64,7 +65,7 @@ type MessagingToolSend = {
 
 function truncateToolText(text: string): string {
   if (text.length <= TOOL_RESULT_MAX_CHARS) return text;
-  return `${text.slice(0, TOOL_RESULT_MAX_CHARS)}\n…(truncated)…`;
+  return `${truncateUtf16Safe(text, TOOL_RESULT_MAX_CHARS)}\n…(truncated)…`;
 }
 
 function sanitizeToolResult(result: unknown): unknown {

src/cron/isolated-agent.ts

@@ -49,7 +49,7 @@ import {
 import { registerAgentRunContext } from "../infra/agent-events.js";
 import { parseTelegramTarget } from "../telegram/targets.js";
 import { resolveTelegramToken } from "../telegram/token.js";
-import { normalizeE164 } from "../utils.js";
+import { normalizeE164, truncateUtf16Safe } from "../utils.js";
 import type { CronJob } from "./types.js";
 
 export type RunCronAgentTurnResult = {
@@ -68,7 +68,7 @@ function pickSummaryFromOutput(text: string | undefined) {
   const clean = (text ?? "").trim();
   if (!clean) return undefined;
   const limit = 2000;
-  return clean.length > limit ? `${clean.slice(0, limit)}…` : clean;
+  return clean.length > limit ? `${truncateUtf16Safe(clean, limit)}…` : clean;
 }
 
 function pickSummaryFromPayloads(

src/cron/service.ts

@@ -1,5 +1,6 @@
 import crypto from "node:crypto";
 
+import { truncateUtf16Safe } from "../utils.js";
 import { computeNextRunAtMs } from "./schedule.js";
 import { loadCronStore, saveCronStore } from "./store.js";
 import type {
@@ -61,7 +62,7 @@ function normalizeOptionalText(raw: unknown) {
 
 function truncateText(input: string, maxLen: number) {
   if (input.length <= maxLen) return input;
-  return `${input.slice(0, Math.max(0, maxLen - 1)).trimEnd()}…`;
+  return `${truncateUtf16Safe(input, Math.max(0, maxLen - 1)).trimEnd()}…`;
 }
 
 function inferLegacyName(job: {

src/discord/monitor.ts

@@ -61,6 +61,7 @@ import {
 } from "../routing/resolve-route.js";
 import { resolveThreadSessionKeys } from "../routing/session-key.js";
 import type { RuntimeEnv } from "../runtime.js";
+import { truncateUtf16Safe } from "../utils.js";
 import { loadWebMedia } from "../web/media.js";
 import { resolveDiscordAccount } from "./accounts.js";
 import { chunkDiscordText } from "./chunk.js";
@@ -1017,7 +1018,10 @@ export function createDiscordMessageHandler(params: {
       }
 
       if (shouldLogVerbose()) {
-        const preview = combinedBody.slice(0, 200).replace(/\n/g, "\\n");
+        const preview = truncateUtf16Safe(combinedBody, 200).replace(
+          /\n/g,
+          "\\n",
+        );
         logVerbose(
           `discord inbound: channel=${message.channelId} from=${ctxPayload.From} preview="${preview}"`,
         );

src/imessage/monitor.ts

@@ -24,6 +24,7 @@ import {
 } from "../pairing/pairing-store.js";
 import { resolveAgentRoute } from "../routing/resolve-route.js";
 import type { RuntimeEnv } from "../runtime.js";
+import { truncateUtf16Safe } from "../utils.js";
 import { resolveIMessageAccount } from "./accounts.js";
 import { createIMessageRpcClient } from "./client.js";
 import { sendMessageIMessage } from "./send.js";
@@ -413,7 +414,7 @@ export async function monitorIMessageProvider(
     }
 
     if (shouldLogVerbose()) {
-      const preview = body.slice(0, 200).replace(/\n/g, "\\n");
+      const preview = truncateUtf16Safe(body, 200).replace(/\n/g, "\\n");
       logVerbose(
         `imessage inbound: chatId=${chatId ?? "unknown"} from=${ctxPayload.From} len=${body.length} preview="${preview}"`,
       );

src/utils.ts

@@ -95,6 +95,61 @@ export function sleep(ms: number) {
   return new Promise((resolve) => setTimeout(resolve, ms));
 }
 
+function isHighSurrogate(codeUnit: number): boolean {
+  return codeUnit >= 0xd800 && codeUnit <= 0xdbff;
+}
+
+function isLowSurrogate(codeUnit: number): boolean {
+  return codeUnit >= 0xdc00 && codeUnit <= 0xdfff;
+}
+
+export function sliceUtf16Safe(
+  input: string,
+  start: number,
+  end?: number,
+): string {
+  const len = input.length;
+
+  let from = start < 0 ? Math.max(len + start, 0) : Math.min(start, len);
+  let to =
+    end === undefined
+      ? len
+      : end < 0
+        ? Math.max(len + end, 0)
+        : Math.min(end, len);
+
+  if (to < from) {
+    const tmp = from;
+    from = to;
+    to = tmp;
+  }
+
+  if (from > 0 && from < len) {
+    const codeUnit = input.charCodeAt(from);
+    if (
+      isLowSurrogate(codeUnit) &&
+      isHighSurrogate(input.charCodeAt(from - 1))
+    ) {
+      from += 1;
+    }
+  }
+
+  if (to > 0 && to < len) {
+    const codeUnit = input.charCodeAt(to - 1);
+    if (isHighSurrogate(codeUnit) && isLowSurrogate(input.charCodeAt(to))) {
+      to -= 1;
+    }
+  }
+
+  return input.slice(from, to);
+}
+
+export function truncateUtf16Safe(input: string, maxLen: number): string {
+  const limit = Math.max(0, Math.floor(maxLen));
+  if (input.length <= limit) return input;
+  return sliceUtf16Safe(input, 0, limit);
+}
+
 export function resolveUserPath(input: string): string {
   const trimmed = input.trim();
   if (!trimmed) return trimmed;