diff --git a/web/src/components/HermesConsoleModal.tsx b/web/src/components/HermesConsoleModal.tsx
index 069dd8a8e0..322e8fd19a 100644
--- a/web/src/components/HermesConsoleModal.tsx
+++ b/web/src/components/HermesConsoleModal.tsx
@@ -12,6 +12,10 @@ import { useModalBehavior } from "@/hooks/useModalBehavior";
 import { useProfileScope } from "@/contexts/useProfileScope";
 import { api } from "@/lib/api";
 import { maybeReloadForLoopbackWsAuthFailure } from "@/lib/dashboard-auth-reload";
+import {
+  refitWhenTerminalFontLoads,
+  TERMINAL_FONT_FAMILY,
+} from "@/lib/terminal-font-refit";
 import { cn, themedBody } from "@/lib/utils";
 import { useTheme } from "@/themes";
 import { errorMessage } from "@/lib/api-error";
@@ -351,8 +355,7 @@ export function HermesConsoleModal({ open, onClose }: HermesConsoleModalProps) {
     const term = new XtermTerminal({
       allowProposedApi: true,
       cursorBlink: true,
-      fontFamily:
-        "'JetBrains Mono', 'Cascadia Mono', 'Fira Code', 'MesloLGS NF', 'Source Code Pro', Menlo, Consolas, 'DejaVu Sans Mono', monospace",
+      fontFamily: TERMINAL_FONT_FAMILY,
       fontSize: 13,
       lineHeight: 1.25,
       letterSpacing: 0,
@@ -394,6 +397,7 @@ export function HermesConsoleModal({ open, onClose }: HermesConsoleModalProps) {
     const ro = new ResizeObserver(scheduleFit);
     ro.observe(host);
     scheduleFit();
+    const stopFontRefit = refitWhenTerminalFontLoads(term, fitTerminal);
 
     const dataDisposable = term.onData(handleInputData);
     setConnectionState("connecting");
@@ -462,6 +466,7 @@ export function HermesConsoleModal({ open, onClose }: HermesConsoleModalProps) {
       dataDisposable.dispose();
       ro.disconnect();
       if (resizeFrame) cancelAnimationFrame(resizeFrame);
+      stopFontRefit();
       wsRef.current?.close();
       wsRef.current = null;
       term.dispose();
diff --git a/web/src/lib/terminal-font-refit.test.ts b/web/src/lib/terminal-font-refit.test.ts
new file mode 100644
index 0000000000..ece0b5d2c3
--- /dev/null
+++ b/web/src/lib/terminal-font-refit.test.ts
@@ -0,0 +1,113 @@
+import { describe, expect, it, vi } from "vitest";
+
+import {
+  refitWhenTerminalFontLoads,
+  TERMINAL_FONT_FAMILY,
+} from "./terminal-font-refit";
+
+/** Mirrors xterm: the cell is re-measured only when fontFamily changes. */
+function fakeTerminal() {
+  let family = TERMINAL_FONT_FAMILY;
+  const term = {
+    measuredWith: [] as string[],
+    options: {
+      get fontFamily() {
+        return family;
+      },
+      set fontFamily(next: string) {
+        if (next === family) return;
+        family = next;
+        term.measuredWith.push(next);
+      },
+    },
+    rows: 24,
+    clearTextureAtlas: vi.fn(),
+    refresh: vi.fn(),
+  };
+  return term;
+}
+
+function deferredFontSet(opts: { loaded?: boolean; faces?: unknown[] } = {}) {
+  let release!: () => void;
+  const gate = new Promise<void>((resolve) => {
+    release = resolve;
+  });
+  return {
+    release,
+    fontSet: {
+      check: vi.fn(() => opts.loaded ?? false),
+      load: vi.fn(async () => {
+        await gate;
+        return (opts.faces ?? [{}]) as FontFace[];
+      }),
+    },
+  };
+}
+
+const settle = () => new Promise((resolve) => setTimeout(resolve, 0));
+
+describe("refitWhenTerminalFontLoads", () => {
+  it("re-measures with the loaded face, then refits and redraws", async () => {
+    const term = fakeTerminal();
+    const fit = vi.fn();
+    const { fontSet, release } = deferredFontSet();
+
+    refitWhenTerminalFontLoads(term, fit, fontSet);
+    await settle();
+    expect(fit).not.toHaveBeenCalled();
+
+    release();
+    await settle();
+
+    expect(term.measuredWith.at(-1)).toBe(TERMINAL_FONT_FAMILY);
+    expect(term.options.fontFamily).toBe(TERMINAL_FONT_FAMILY);
+    expect(fit).toHaveBeenCalledTimes(1);
+    expect(term.clearTextureAtlas).toHaveBeenCalledTimes(1);
+    expect(term.refresh).toHaveBeenCalledWith(0, 23);
+  });
+
+  it("does nothing after cleanup runs before the font arrives", async () => {
+    const term = fakeTerminal();
+    const fit = vi.fn();
+    const { fontSet, release } = deferredFontSet();
+
+    const cleanup = refitWhenTerminalFontLoads(term, fit, fontSet);
+    cleanup();
+    release();
+    await settle();
+
+    expect(term.measuredWith).toEqual([]);
+    expect(fit).not.toHaveBeenCalled();
+  });
+
+  it("skips the refit when the faces were already loaded at open()", async () => {
+    const term = fakeTerminal();
+    const fit = vi.fn();
+    const { fontSet } = deferredFontSet({ loaded: true });
+
+    refitWhenTerminalFontLoads(term, fit, fontSet);
+    await settle();
+
+    expect(fontSet.load).not.toHaveBeenCalled();
+    expect(fit).not.toHaveBeenCalled();
+  });
+
+  it("leaves fallback metrics alone when no bundled face could load", async () => {
+    const term = fakeTerminal();
+    const fit = vi.fn();
+    const { fontSet, release } = deferredFontSet({ faces: [] });
+
+    refitWhenTerminalFontLoads(term, fit, fontSet);
+    release();
+    await settle();
+
+    expect(term.measuredWith).toEqual([]);
+    expect(fit).not.toHaveBeenCalled();
+  });
+
+  it("is a no-op without a FontFaceSet", () => {
+    const fit = vi.fn();
+    expect(() => refitWhenTerminalFontLoads(fakeTerminal(), fit, undefined)()).not.toThrow();
+    expect(fit).not.toHaveBeenCalled();
+  });
+});
diff --git a/web/src/lib/terminal-font-refit.ts b/web/src/lib/terminal-font-refit.ts
new file mode 100644
index 0000000000..2e63c13352
--- /dev/null
+++ b/web/src/lib/terminal-font-refit.ts
@@ -0,0 +1,71 @@
+/**
+ * Dashboard xterm font stack. 'JetBrains Mono' is bundled via @font-face in
+ * index.css with `font-display: swap`, so it is usually still downloading
+ * when a terminal first opens.
+ */
+export const TERMINAL_FONT_FAMILY =
+  "'JetBrains Mono', 'Cascadia Mono', 'Fira Code', 'MesloLGS NF', 'Source Code Pro', Menlo, Consolas, 'DejaVu Sans Mono', monospace";
+
+const BUNDLED_FACES = ["400", "700", "italic 400"].map(
+  (descriptor) => `${descriptor} 1em 'JetBrains Mono'`,
+);
+
+type TerminalFontSet = Pick<FontFaceSet, "check" | "load">;
+
+export interface RemeasurableTerminal {
+  options: { fontFamily?: string };
+  rows: number;
+  clearTextureAtlas(): void;
+  refresh(start: number, end: number): void;
+}
+
+function browserFontSet(): TerminalFontSet | undefined {
+  return typeof document === "undefined" ? undefined : document.fonts;
+}
+
+/**
+ * xterm measures its cell size once at open() and afterwards only when
+ * fontFamily/fontSize *change* or the grid resizes. When the bundled font
+ * swaps in later, the grid keeps fallback-font metrics (and the WebGL atlas
+ * keeps fallback glyphs) until something resizes the host, e.g. toggling the
+ * sidebar (#92899). Once the bundled faces load, force a re-measure, refit,
+ * and redraw. Returns a cleanup that drops a still-pending load.
+ */
+export function refitWhenTerminalFontLoads(
+  term: RemeasurableTerminal,
+  fit: () => void,
+  fontSet: TerminalFontSet | undefined = browserFontSet(),
+): () => void {
+  if (!fontSet?.load) return () => undefined;
+  try {
+    if (BUNDLED_FACES.every((face) => fontSet.check(face))) {
+      return () => undefined;
+    }
+  } catch {
+    /* check() throws on unparsable descriptors in some engines; just load */
+  }
+
+  let cancelled = false;
+  void Promise.allSettled(
+    BUNDLED_FACES.map((face) => Promise.resolve().then(() => fontSet.load(face))),
+  ).then((results) => {
+    if (cancelled) return;
+    const loaded = results.some(
+      (r) => r.status === "fulfilled" && r.value.length > 0,
+    );
+    if (!loaded) return;
+
+    // A same-value assignment is a no-op in xterm, so bounce through a
+    // generic family to make it re-measure against the loaded face.
+    const family = term.options.fontFamily ?? TERMINAL_FONT_FAMILY;
+    term.options.fontFamily = "monospace";
+    term.options.fontFamily = family;
+    fit();
+    term.clearTextureAtlas();
+    if (term.rows > 0) term.refresh(0, term.rows - 1);
+  });
+
+  return () => {
+    cancelled = true;
+  };
+}
diff --git a/web/src/pages/ChatPage.test.tsx b/web/src/pages/ChatPage.test.tsx
index 035af07580..203c7ec9f8 100644
--- a/web/src/pages/ChatPage.test.tsx
+++ b/web/src/pages/ChatPage.test.tsx
@@ -43,6 +43,8 @@ class FakeTerminal {
 
   clearSelection() {}
 
+  clearTextureAtlas() {}
+
   dispose() {}
 
   focus() {}
@@ -579,6 +581,46 @@ describe("ChatPage side panel collapse", () => {
 // (that timer is set after `new WebSocket`). Without its own deadline the tab
 // strands on "connecting" with no retry. Mirrors the ChatSidebar events-feed
 // coverage in src/components/ChatSidebar.test.tsx.
+describe("ChatPage bundled font swap-in", () => {
+  it("redraws the terminal with the bundled font once it finishes loading", async () => {
+    let releaseFont!: () => void;
+    const fontGate = new Promise<void>((resolve) => {
+      releaseFont = resolve;
+    });
+    Object.defineProperty(document, "fonts", {
+      configurable: true,
+      value: {
+        check: () => false,
+        load: async () => {
+          await fontGate;
+          return [{}];
+        },
+      },
+    });
+    const clearAtlas = vi.spyOn(FakeTerminal.prototype, "clearTextureAtlas");
+    try {
+      const { default: ChatPage } = await import("./ChatPage");
+      await render(
+        <MemoryRouter initialEntries={["/chat"]}>
+          <ChatPage isActive />
+        </MemoryRouter>,
+      );
+      expect(clearAtlas).not.toHaveBeenCalled();
+
+      await act(async () => {
+        releaseFont();
+        await fontGate;
+        await new Promise((resolve) => setTimeout(resolve, 0));
+      });
+
+      expect(clearAtlas).toHaveBeenCalledTimes(1);
+    } finally {
+      clearAtlas.mockRestore();
+      delete (document as { fonts?: unknown }).fonts;
+    }
+  });
+});
+
 describe("ChatPage PTY ticket connect deadline", () => {
   beforeEach(() => {
     vi.useFakeTimers();
diff --git a/web/src/pages/ChatPage.tsx b/web/src/pages/ChatPage.tsx
index 2a97574dfa..dafdde133f 100644
--- a/web/src/pages/ChatPage.tsx
+++ b/web/src/pages/ChatPage.tsx
@@ -94,6 +94,10 @@ import {
   type PtyBannerAction,
 } from "@/lib/pty-close-copy";
 import { ptyAttachToken } from "@/lib/pty-attach-token";
+import {
+  refitWhenTerminalFontLoads,
+  TERMINAL_FONT_FAMILY,
+} from "@/lib/terminal-font-refit";
 import { loseWebglContexts } from "@/lib/xterm-webgl-release";
 import { PluginSlot } from "@/plugins";
 import { useTheme } from "@/themes";
@@ -579,8 +583,7 @@ export default function ChatPage({ isActive = true }: { isActive?: boolean }) {
     const term = new Terminal({
       allowProposedApi: true,
       cursorBlink: true,
-      fontFamily:
-        "'JetBrains Mono', 'Cascadia Mono', 'Fira Code', 'MesloLGS NF', 'Source Code Pro', Menlo, Consolas, 'DejaVu Sans Mono', monospace",
+      fontFamily: TERMINAL_FONT_FAMILY,
       fontSize: terminalFontSizeForWidth(tierW0),
       lineHeight: terminalLineHeightForWidth(tierW0),
       letterSpacing: 0,
@@ -1112,6 +1115,10 @@ export default function ChatPage({ isActive = true }: { isActive?: boolean }) {
       });
     });
 
+    // The rAF fits above still measure the fallback font if JetBrains Mono
+    // hasn't swapped in yet (#92899).
+    const stopFontRefit = refitWhenTerminalFontLoads(term, syncTerminalMetrics);
+
     // WebSocket. In gated mode (``window.__HERMES_AUTH_REQUIRED__``) this
     // awaits a single-use ticket via /api/auth/ws-ticket before opening;
     // in loopback mode it resolves synchronously against the injected
@@ -1607,6 +1614,7 @@ export default function ChatPage({ isActive = true }: { isActive?: boolean }) {
       if (hostSyncRaf) cancelAnimationFrame(hostSyncRaf);
       if (settleRaf1) cancelAnimationFrame(settleRaf1);
       if (settleRaf2) cancelAnimationFrame(settleRaf2);
+      stopFontRefit();
       clearReconnectTimer();
       clearConnectingTimer();
       clearTicketTimer();