diff --git a/web/src/v2/thread-export.test.ts b/web/src/v2/thread-export.test.ts
index 0291cd39..9ecab880 100644
--- a/web/src/v2/thread-export.test.ts
+++ b/web/src/v2/thread-export.test.ts
@@ -113,6 +113,19 @@ it("merges duplicate public assistant endings and labels pending and withdrawn i
   expect(filename).not.toMatch(/[\\/:*?"<>|\u0000-\u001f]/u);
 });
 
+it("truncates export filenames without splitting Unicode or ending in separators", () => {
+  const prefix = "a".repeat(99);
+  expect(threadExportFilename(`${prefix}😀suffix`, "markdown")).toBe(`conversation-${prefix}😀.md`);
+  expect(threadExportFilename(`${prefix} tail`, "text")).toBe(`conversation-${prefix}.txt`);
+});
+
+it("keeps ZWJ emoji families whole when truncating export filenames", () => {
+  const family = "👨‍👩‍👧‍👦";
+  const prefix = "a".repeat(99);
+  expect(threadExportFilename(`${prefix}${family}tail`, "markdown")).toBe(`conversation-${prefix}${family}.md`);
+  expect(threadExportFilename(`${prefix}a${family}`, "text")).toBe(`conversation-${prefix}a.txt`);
+});
+
 it("rejects missing full bodies instead of returning partial history", async () => {
   const get = vi.fn(async (path: string) => {
     if (path.endsWith("second")) throw new Error("body unavailable");
diff --git a/web/src/v2/thread-export.ts b/web/src/v2/thread-export.ts
index 36bed15a..c02cda78 100644
--- a/web/src/v2/thread-export.ts
+++ b/web/src/v2/thread-export.ts
@@ -81,7 +81,26 @@ export function formatThreadExport(title: string, messages: ExportMessage[], for
   return `${format === "markdown" ? "# " : ""}${heading}\n\n${sections.join("\n\n---\n\n")}\n`;
 }
 
+// Truncate by user-perceived character, not by code point: ZWJ emoji families,
+// skin-tone modifiers and combining marks each count as one grapheme, so the
+// bound can never split them into invalid or unrecognizable fragments. Runtimes
+// without Intl.Segmenter keep the code-point bound as a floor.
+function truncateExportTitleGraphemes(value: string, maxGraphemes: number): string {
+  if (typeof Intl === "undefined" || !("Segmenter" in Intl)) {
+    return [...value].slice(0, maxGraphemes).join("");
+  }
+  let name = "";
+  let count = 0;
+  for (const segment of new Intl.Segmenter(undefined, { granularity: "grapheme" }).segment(value)) {
+    if (count >= maxGraphemes) break;
+    name += segment.segment;
+    count += 1;
+  }
+  return name;
+}
+
 export function threadExportFilename(title: string, format: ThreadExportFormat): string {
-  const name = title.replace(/[\\/:*?"<>|\u0000-\u001f]/gu, "_").trim().replace(/[. ]+$/u, "").slice(0, 100);
+  const clean = title.replace(/[\\/:*?"<>|\u0000-\u001f]/gu, "_").trim().replace(/[. ]+$/u, "");
+  const name = truncateExportTitleGraphemes(clean, 100).replace(/[. ]+$/u, "");
   return `conversation-${name || "export"}.${format === "markdown" ? "md" : "txt"}`;
 }