Fix terminal resize after splitting panes (#1249)

docs/architecture.md

@@ -183,6 +183,8 @@ Terminal I/O is sent as binary WebSocket frames decoded by `decodeTerminalStream
 - 1-byte slot: terminal slot id
 - variable payload: bytes for output/input, JSON-encoded `{ rows, cols }` for resize, terminal snapshot for snapshot
 
+Terminal PTY size is last-interacting-client-wins. A client claims the PTY size only when its terminal viewport genuinely changes size or the user focuses/taps the terminal. Passive rendering work — attaching, restoring visibility, font settling, renderer refits, or just looking at a visible terminal — must not send a resize frame. The server does not broadcast resize ownership; the resized PTY redraws through normal output, and every attached client renders that output in its own local viewport.
+
 There is also a separate file-transfer binary frame format in the same directory, used for download/upload streams.
 
 ### Compatibility rules

packages/app/e2e/terminal-split-resize.spec.ts

@@ -0,0 +1,119 @@
+import type { Page } from "@playwright/test";
+import { test, expect } from "./fixtures";
+import { TerminalE2EHarness, withTerminalInApp } from "./helpers/terminal-dsl";
+import { getTerminalBufferText, waitForTerminalContent } from "./helpers/terminal-perf";
+
+interface TerminalSize {
+  rows: number | null;
+  cols: number | null;
+}
+
+// The xterm/client view resizes immediately on split, so it is not enough to
+// prove the bug. It is the misleading symptom.
+async function readXtermSize(page: Page): Promise<TerminalSize> {
+  return page.evaluate(() => {
+    const term = (window as Window & { __paseoTerminal?: { rows?: number; cols?: number } })
+      .__paseoTerminal;
+    return {
+      rows: typeof term?.rows === "number" ? term.rows : null,
+      cols: typeof term?.cols === "number" ? term.cols : null,
+    };
+  });
+}
+
+// The PTY's own view of its size, reported by an `stty size` loop running in the
+// shell. This needs no focus or click, so it observes whether the daemon-side PTY
+// actually received the resize frame after the split.
+async function readLatestPtySize(page: Page): Promise<TerminalSize | null> {
+  const text = await getTerminalBufferText(page);
+  const matches = [...text.matchAll(/PTYSIZE (\d+) (\d+)/g)];
+  const last = matches.at(-1);
+  if (!last) {
+    return null;
+  }
+  return { rows: Number(last[1]), cols: Number(last[2]) };
+}
+
+function hasPtySizeReport(text: string): boolean {
+  return /PTYSIZE \d+ \d+/.test(text);
+}
+
+async function readXtermRows(page: Page): Promise<number | null> {
+  return (await readXtermSize(page)).rows;
+}
+
+async function ptyRowsMatchXtermRows(page: Page): Promise<boolean> {
+  const xterm = await readXtermSize(page);
+  const pty = await readLatestPtySize(page);
+  return pty?.rows === xterm.rows;
+}
+
+async function verifySplitDownResizesPty(page: Page, harness: TerminalE2EHarness): Promise<void> {
+  await page.setViewportSize({ width: 1280, height: 900 });
+
+  await withTerminalInApp(page, harness, { name: "split-resize" }, async () => {
+    await harness.setupPrompt(page);
+
+    const terminal = harness.terminalSurface(page);
+    // Continuously echo the PTY's own size. `stty size` prints "rows cols" and
+    // reads the controlling tty, so this keeps reporting the real PTY size
+    // without the test ever clicking the terminal back into focus.
+    await terminal.pressSequentially(
+      'while true; do echo "PTYSIZE $(stty size)"; sleep 0.3; done\n',
+      { delay: 0 },
+    );
+    await waitForTerminalContent(page, hasPtySizeReport, 10_000);
+
+    const beforeXterm = await readXtermSize(page);
+    const beforePty = await readLatestPtySize(page);
+    expect(beforePty, "the PTY should report its size before splitting").not.toBeNull();
+    expect(beforeXterm.rows, "xterm should report its row count before splitting").not.toBeNull();
+    expect(beforePty?.rows, "while focused, the PTY size should already match the xterm size").toBe(
+      beforeXterm.rows,
+    );
+
+    // Split the pane downward. This focuses the new empty pane, so the terminal
+    // pane is unfocused at the exact moment its container shrinks.
+    await page.getByRole("button", { name: "Split pane down" }).first().click();
+
+    // The local xterm renderer shrinks immediately on split - the part of the
+    // behaviour that already works and that makes the bug look like nothing changed.
+    await expect
+      .poll(() => readXtermRows(page), {
+        message: "xterm should shrink after splitting the pane down",
+        timeout: 8_000,
+      })
+      .toBeLessThan(beforeXterm.rows ?? Number.POSITIVE_INFINITY);
+
+    // The PTY must follow the shrunken terminal, even though focus moved to the
+    // new pane. Today it stays stuck at the pre-split size until the terminal is
+    // clicked back into focus. This poll fails without the fix.
+    await expect
+      .poll(() => ptyRowsMatchXtermRows(page), {
+        message: "the PTY rows should match the resized terminal after split-down",
+        timeout: 8_000,
+      })
+      .toBe(true);
+  });
+}
+
+test.describe("Terminal split resize", () => {
+  test.describe.configure({ timeout: 120_000 });
+
+  let harness: TerminalE2EHarness;
+
+  test.beforeAll(async () => {
+    harness = await TerminalE2EHarness.create({ tempPrefix: "terminal-split-resize-" });
+  });
+
+  test.afterAll(async () => {
+    await harness?.cleanup();
+  });
+
+  test("splitting the pane down resizes the PTY even though focus moves to the new pane", async ({
+    page,
+  }) => {
+    test.setTimeout(90_000);
+    await verifySplitDownResizesPty(page, harness);
+  });
+});

packages/app/src/components/terminal-emulator.native.tsx

@@ -50,7 +50,8 @@ interface TerminalEmulatorProps {
   onSwipeRight?: () => void;
   initialSnapshot?: TerminalState | null;
   onInput?: (data: string) => Promise<void> | void;
-  onResize?: (input: { rows: number; cols: number }) => Promise<void> | void;
+  onFocus?: () => Promise<void> | void;
+  onResize?: (input: { rows: number; cols: number; shouldClaim: boolean }) => Promise<void> | void;
   onTerminalKey?: (input: {
     key: string;
     ctrl: boolean;
@@ -89,7 +90,7 @@ type BridgeInboundMessage =
   | { type: "renderSnapshot"; streamKey: string; state: TerminalState | null }
   | { type: "clear"; streamKey: string }
   | { type: "focus"; streamKey: string; forceRefocus?: boolean }
-  | { type: "resize"; streamKey: string }
+  | { type: "resize"; streamKey: string; shouldClaim?: boolean }
   | { type: "setTheme"; streamKey: string; theme: ITheme }
   | { type: "setScrollback"; streamKey: string; lines: number }
   | { type: "setPendingModifiers"; streamKey: string; pendingModifiers: PendingTerminalModifiers }
@@ -105,7 +106,7 @@ type BridgeOutboundMessage =
   | { type: "bridgeReady" }
   | { type: "rendererReady"; streamKey: string; isReady: boolean }
   | { type: "input"; streamKey: string; data: string }
-  | { type: "resize"; streamKey: string; rows: number; cols: number }
+  | { type: "resize"; streamKey: string; rows: number; cols: number; shouldClaim?: boolean }
   | {
       type: "terminalKey";
       streamKey: string;
@@ -188,6 +189,7 @@ export default function TerminalEmulator({
   onSwipeRight,
   initialSnapshot = null,
   onInput,
+  onFocus,
   onResize,
   onTerminalKey,
   onPendingModifiersConsumed,
@@ -229,6 +231,7 @@ export default function TerminalEmulator({
   };
   const callbacksRef = useRef({
     onInput,
+    onFocus,
     onResize,
     onTerminalKey,
     onPendingModifiersConsumed,
@@ -241,6 +244,7 @@ export default function TerminalEmulator({
   });
   callbacksRef.current = {
     onInput,
+    onFocus,
     onResize,
     onTerminalKey,
     onPendingModifiersConsumed,
@@ -401,14 +405,14 @@ export default function TerminalEmulator({
 
   useEffect(() => {
     if (focusRequestToken <= 0) return;
-    sendToWebView({ type: "resize", streamKey });
+    sendToWebView({ type: "resize", streamKey, shouldClaim: true });
     sendToWebView({ type: "focus", streamKey });
     webViewRef.current?.requestFocus();
   }, [focusRequestToken, sendToWebView, streamKey]);
 
   useEffect(() => {
     if (resizeRequestToken <= 0) return;
-    sendToWebView({ type: "resize", streamKey });
+    sendToWebView({ type: "resize", streamKey, shouldClaim: true });
   }, [resizeRequestToken, sendToWebView, streamKey]);
 
   useEffect(() => {
@@ -495,7 +499,11 @@ export default function TerminalEmulator({
           callbacksRef.current.onInput?.(message.data);
           break;
         case "resize":
-          callbacksRef.current.onResize?.({ rows: message.rows, cols: message.cols });
+          callbacksRef.current.onResize?.({
+            rows: message.rows,
+            cols: message.cols,
+            shouldClaim: message.shouldClaim !== false,
+          });
           break;
         case "terminalKey":
           callbacksRef.current.onTerminalKey?.({
@@ -592,6 +600,7 @@ export default function TerminalEmulator({
       return;
     }
     webViewRef.current?.requestFocus();
+    callbacksRef.current.onFocus?.();
     sendToWebView({ type: "focus", streamKey, forceRefocus: true });
   }, [sendToWebView, streamKey]);
 

packages/app/src/components/terminal-emulator.tsx

@@ -139,7 +139,8 @@ interface TerminalEmulatorProps {
   onSwipeRight?: () => void;
   initialSnapshot?: TerminalState | null;
   onInput?: (data: string) => Promise<void> | void;
-  onResize?: (input: { rows: number; cols: number }) => Promise<void> | void;
+  onFocus?: () => Promise<void> | void;
+  onResize?: (input: { rows: number; cols: number; shouldClaim: boolean }) => Promise<void> | void;
   onTerminalKey?: (input: {
     key: string;
     ctrl: boolean;
@@ -219,6 +220,7 @@ export default function TerminalEmulator({
   onSwipeRight,
   initialSnapshot = null,
   onInput,
+  onFocus,
   onResize,
   onTerminalKey,
   onPendingModifiersConsumed,
@@ -527,7 +529,7 @@ export default function TerminalEmulator({
     if (focusRequestToken <= 0) {
       return () => {};
     }
-    runtimeRef.current?.resize({ force: true });
+    runtimeRef.current?.resize({ force: true, shouldClaim: true });
     return focusWithRetries({
       focus: () => {
         runtimeRef.current?.focus();
@@ -547,7 +549,7 @@ export default function TerminalEmulator({
     if (resizeRequestToken <= 0) {
       return;
     }
-    runtimeRef.current?.resize({ force: true });
+    runtimeRef.current?.resize({ force: true, shouldClaim: true });
   }, [resizeRequestToken]);
 
   useEffect(() => {
@@ -742,8 +744,9 @@ export default function TerminalEmulator({
   }, []);
 
   const handleRootPointerDown = useCallback(() => {
+    onFocus?.();
     runtimeRef.current?.focus();
-  }, []);
+  }, [onFocus]);
 
   const handleRootContextMenu = useCallback(
     (event: ReactMouseEvent) => {

packages/app/src/components/terminal-pane.tsx

@@ -214,6 +214,7 @@ export function TerminalPane({
   const pendingTerminalInputRef = useRef<PendingTerminalInput[]>([]);
   const keyboardRefitTimeoutsRef = useRef<Array<ReturnType<typeof setTimeout>>>([]);
   const lastAutoFocusKeyRef = useRef<string | null>(null);
+  const lastPaneFocusResizeKeyRef = useRef<string | null>(null);
   const initialSnapshot = workspaceTerminalSession.snapshots.get({ terminalId });
 
   useEffect(() => {
@@ -252,7 +253,7 @@ export function TerminalPane({
   );
 
   useEffect(() => {
-    if (isMobile || !isWorkspaceFocused || !isPaneFocused || !terminalId) {
+    if (isMobile || !isPaneFocused || !terminalId) {
       lastAutoFocusKeyRef.current = null;
       return;
     }
@@ -263,15 +264,36 @@ export function TerminalPane({
     }
 
     lastAutoFocusKeyRef.current = nextFocusKey;
+    if (!isWorkspaceFocused) {
+      return;
+    }
+
     requestTerminalFocus();
   }, [isMobile, isPaneFocused, isWorkspaceFocused, requestTerminalFocus, scopeKey, terminalId]);
 
   useEffect(() => {
-    if (isPaneFocused && isWorkspaceFocused && isAppVisible && terminalId) {
-      lastSentTerminalSizeRef.current = null;
-      requestTerminalReflow();
+    if (!isPaneFocused || !terminalId) {
+      lastPaneFocusResizeKeyRef.current = null;
+      return;
     }
-  }, [isAppVisible, isPaneFocused, isWorkspaceFocused, requestTerminalReflow, terminalId]);
+
+    const focusResizeKey = `${scopeKey}:${terminalId}`;
+    if (lastPaneFocusResizeKeyRef.current === focusResizeKey) {
+      return;
+    }
+    lastPaneFocusResizeKeyRef.current = focusResizeKey;
+    if (!isWorkspaceFocused) {
+      return;
+    }
+
+    lastSentTerminalSizeRef.current = null;
+    requestTerminalReflow();
+  }, [isPaneFocused, isWorkspaceFocused, requestTerminalReflow, scopeKey, terminalId]);
+
+  const handleTerminalFocus = useCallback(() => {
+    lastSentTerminalSizeRef.current = null;
+    requestTerminalReflow();
+  }, [requestTerminalReflow]);
 
   const clearKeyboardRefitTimeouts = useCallback(() => {
     if (keyboardRefitTimeoutsRef.current.length === 0) {
@@ -308,25 +330,6 @@ export function TerminalPane({
     [pulseKeyboardRefits],
   );
 
-  useEffect(() => {
-    if (!isWorkspaceFocused || !terminalId) {
-      return;
-    }
-    // Focus transitions can temporarily report stale dimensions.
-    // Pulse forced refits so xterm fills the pane when returning to a terminal.
-    const timeoutHandles = TERMINAL_REFIT_DELAYS_MS.map((delayMs) =>
-      setTimeout(() => {
-        requestTerminalReflow();
-      }, delayMs),
-    );
-
-    return () => {
-      for (const handle of timeoutHandles) {
-        clearTimeout(handle);
-      }
-    };
-  }, [isWorkspaceFocused, requestTerminalReflow, terminalId]);
-
   useEffect(() => {
     if (!client || !isConnected || !isWorkspaceFocused) {
       return;
@@ -375,7 +378,7 @@ export function TerminalPane({
 
     const controller = new TerminalStreamController({
       client,
-      getPreferredSize: () => measuredTerminalSizeRef.current,
+      getPreferredSize: () => lastSentTerminalSizeRef.current,
       onOutput: ({ terminalId: outputTerminalId, data }) => {
         if (!isWorkspaceFocused || terminalIdRef.current !== outputTerminalId) {
           return;
@@ -605,33 +608,35 @@ export function TerminalPane({
     ],
   );
 
-  const handleTerminalResize = useStableEvent((input: { rows: number; cols: number }) => {
-    const { rows, cols } = input;
-    if (rows <= 0 || cols <= 0) {
-      return;
-    }
-    const normalizedRows = Math.floor(rows);
-    const normalizedCols = Math.floor(cols);
-    const nextSize = { rows: normalizedRows, cols: normalizedCols };
-    measuredTerminalSizeRef.current = nextSize;
-    if (!client || !terminalId || !isPaneFocused || !isWorkspaceFocused || !isAppVisible) {
-      return;
-    }
-    const previousSent = lastSentTerminalSizeRef.current;
-    if (
-      previousSent &&
-      previousSent.rows === normalizedRows &&
-      previousSent.cols === normalizedCols
-    ) {
-      return;
-    }
-    lastSentTerminalSizeRef.current = nextSize;
-    client.sendTerminalInput(terminalId, {
-      type: "resize",
-      rows: normalizedRows,
-      cols: normalizedCols,
-    });
-  });
+  const handleTerminalResize = useStableEvent(
+    (input: { rows: number; cols: number; shouldClaim: boolean }) => {
+      const { rows, cols } = input;
+      if (rows <= 0 || cols <= 0) {
+        return;
+      }
+      const normalizedRows = Math.floor(rows);
+      const normalizedCols = Math.floor(cols);
+      const nextSize = { rows: normalizedRows, cols: normalizedCols };
+      measuredTerminalSizeRef.current = nextSize;
+      if (!input.shouldClaim || !client || !terminalId || !isWorkspaceFocused || !isAppVisible) {
+        return;
+      }
+      const previousSent = lastSentTerminalSizeRef.current;
+      if (
+        previousSent &&
+        previousSent.rows === normalizedRows &&
+        previousSent.cols === normalizedCols
+      ) {
+        return;
+      }
+      lastSentTerminalSizeRef.current = nextSize;
+      client.sendTerminalInput(terminalId, {
+        type: "resize",
+        rows: normalizedRows,
+        cols: normalizedCols,
+      });
+    },
+  );
 
   const handleTerminalKey = useCallback(
     async (input: { key: string; ctrl: boolean; shift: boolean; alt: boolean; meta: boolean }) => {
@@ -764,6 +769,7 @@ export function TerminalPane({
               onSwipeRight={handleSwipeRight}
               onSwipeLeft={handleSwipeLeft}
               onInput={handleTerminalData}
+              onFocus={handleTerminalFocus}
               onResize={handleTerminalResize}
               onTerminalKey={handleTerminalKey}
               onInputModeChange={handleInputModeChange}

packages/app/src/terminal/runtime/terminal-emulator-runtime.browser.test.ts

@@ -14,6 +14,7 @@ vi.mock("@xterm/addon-webgl", () => ({
 interface TerminalSize {
   rows: number;
   cols: number;
+  shouldClaim: boolean;
 }
 
 interface TerminalKeyRecord {
@@ -198,6 +199,15 @@ describe("terminal emulator runtime in a real browser", () => {
     expect(window.__paseoTerminal?.options.scrollback).toBe(42_000);
   });
 
+  it("does not claim PTY ownership from passive mount refits", async () => {
+    await page.viewport(900, 600);
+    const mounted = createTerminalHost({ width: 720, height: 360 });
+
+    await waitFor({ predicate: () => mounted.sizes.length > 0 });
+
+    expect(mounted.sizes[0]?.shouldClaim).toBe(false);
+  });
+
   it("reports a larger PTY size when the terminal container grows", async () => {
     await page.viewport(900, 600);
     const mounted = createTerminalHost({ width: 360, height: 180 });
@@ -220,6 +230,7 @@ describe("terminal emulator runtime in a real browser", () => {
     const grownSize = latestSize(mounted.sizes);
     expect(grownSize.cols).toBeGreaterThan(initialSize.cols);
     expect(grownSize.rows).toBeGreaterThan(initialSize.rows);
+    expect(grownSize.shouldClaim).toBe(true);
   });
 
   it("refreshes visible rows on a forced same-size resize", async () => {

packages/app/src/terminal/runtime/terminal-emulator-runtime.test.ts

@@ -91,6 +91,10 @@ interface StubTerminal {
   cols?: number;
 }
 
+interface RuntimeFitProbe {
+  fitAndEmitResize: (input?: { force?: boolean; shouldClaim?: boolean }) => void;
+}
+
 function createRuntimeWithTerminal(): {
   runtime: TerminalEmulatorRuntime;
   terminal: StubTerminal & {
@@ -328,14 +332,13 @@ describe("terminal-emulator-runtime", () => {
     const runtime = new TerminalEmulatorRuntime();
     const fitAndEmitResize = vi.fn();
 
-    (runtime as unknown as { fitAndEmitResize: (force: boolean) => void }).fitAndEmitResize =
-      fitAndEmitResize;
+    (runtime as unknown as RuntimeFitProbe).fitAndEmitResize = fitAndEmitResize;
 
     runtime.resize();
     runtime.resize({ force: true });
 
-    expect(fitAndEmitResize).toHaveBeenNthCalledWith(1, false);
-    expect(fitAndEmitResize).toHaveBeenNthCalledWith(2, true);
+    expect(fitAndEmitResize).toHaveBeenNthCalledWith(1, undefined);
+    expect(fitAndEmitResize).toHaveBeenNthCalledWith(2, { force: true });
   });
 
   it("updates terminal theme without remounting", () => {
@@ -381,12 +384,11 @@ describe("terminal-emulator-runtime", () => {
     expect(refresh).toHaveBeenCalledWith(0, 11);
   });
 
-  it("forces a refit when the page becomes visible again", () => {
+  it("passively refits when the page becomes visible again", () => {
     const runtime = new TerminalEmulatorRuntime();
     const fitAndEmitResize = vi.fn();
 
-    (runtime as unknown as { fitAndEmitResize: (force: boolean) => void }).fitAndEmitResize =
-      fitAndEmitResize;
+    (runtime as unknown as RuntimeFitProbe).fitAndEmitResize = fitAndEmitResize;
     (globalThis as { document?: { visibilityState?: string } }).document = {
       visibilityState: "visible",
     };
@@ -397,15 +399,14 @@ describe("terminal-emulator-runtime", () => {
       }
     ).handleVisibilityRestore();
 
-    expect(fitAndEmitResize).toHaveBeenCalledWith(true);
+    expect(fitAndEmitResize).toHaveBeenCalledWith({ force: true, shouldClaim: false });
   });
 
   it("does not refit while the page is still hidden", () => {
     const runtime = new TerminalEmulatorRuntime();
     const fitAndEmitResize = vi.fn();
 
-    (runtime as unknown as { fitAndEmitResize: (force: boolean) => void }).fitAndEmitResize =
-      fitAndEmitResize;
+    (runtime as unknown as RuntimeFitProbe).fitAndEmitResize = fitAndEmitResize;
     (globalThis as { document?: { visibilityState?: string } }).document = {
       visibilityState: "hidden",
     };

packages/app/src/terminal/runtime/terminal-emulator-runtime.ts

@@ -41,7 +41,7 @@ export interface TerminalEmulatorRuntimeMountInput {
 
 export interface TerminalEmulatorRuntimeCallbacks {
   onInput?: (data: string) => Promise<void> | void;
-  onResize?: (input: { rows: number; cols: number }) => Promise<void> | void;
+  onResize?: (input: { rows: number; cols: number; shouldClaim: boolean }) => Promise<void> | void;
   onTerminalKey?: (input: {
     key: string;
     ctrl: boolean;
@@ -68,7 +68,6 @@ interface TerminalEmulatorRuntimeDisposables {
   removeWindowFocus: () => void;
   removeDocumentVisibilityChange: () => void;
   removeVisualViewportResize: () => void;
-  clearFitInterval: () => void;
   clearFitTimeouts: () => void;
   removeFontListeners: () => void;
   removeTouchListeners: () => void;
@@ -164,7 +163,8 @@ export class TerminalEmulatorRuntime {
   };
   private terminal: Terminal | null = null;
   private fitAddon: FitAddon | null = null;
-  private fitAndEmitResize: ((force: boolean) => void) | null = null;
+  private fitAndEmitResize: ((input?: { force?: boolean; shouldClaim?: boolean }) => void) | null =
+    null;
   private lastSize: { rows: number; cols: number } | null = null;
   private cleanup: (() => void) | null = null;
   private outputOperations: TerminalOutputOperation[] = [];
@@ -181,10 +181,10 @@ export class TerminalEmulatorRuntime {
       return;
     }
 
-    this.fitAndEmitResize?.(true);
+    this.fitAndEmitResize?.({ force: true, shouldClaim: false });
     if (typeof window.requestAnimationFrame === "function") {
       window.requestAnimationFrame(() => {
-        this.fitAndEmitResize?.(true);
+        this.fitAndEmitResize?.({ force: true, shouldClaim: false });
       });
     }
   };
@@ -281,7 +281,7 @@ export class TerminalEmulatorRuntime {
       webglAddon = null;
       disposeImageAddon();
       // WebGL and DOM renderers can have different cell dimensions.
-      this.fitAndEmitResize?.(true);
+      this.fitAndEmitResize?.({ force: true, shouldClaim: false });
     };
 
     // Browser xterm is a renderer only; it never replies to terminal protocol queries.
@@ -319,7 +319,7 @@ export class TerminalEmulatorRuntime {
         imageAddon = new ImageAddon();
         terminal.loadAddon(imageAddon);
         registerProtocolQuerySuppression();
-        this.fitAndEmitResize?.(true);
+        this.fitAndEmitResize?.({ force: true, shouldClaim: false });
       } catch {
         disposeWebglRenderer();
       }
@@ -336,7 +336,9 @@ export class TerminalEmulatorRuntime {
     this.fitAddon = fitAddon;
     window.__paseoTerminal = terminal;
 
-    const fitAndEmitResize = (force: boolean): void => {
+    const fitAndEmitResize = (resizeInput?: { force?: boolean; shouldClaim?: boolean }): void => {
+      const force = resizeInput?.force ?? false;
+      const shouldClaim = resizeInput?.shouldClaim ?? true;
       const currentTerminal = this.terminal;
       const currentFitAddon = this.fitAddon;
       if (!currentTerminal || !currentFitAddon) {
@@ -365,11 +367,12 @@ export class TerminalEmulatorRuntime {
       this.callbacks.onResize?.({
         rows: nextRows,
         cols: nextCols,
+        shouldClaim,
       });
     };
     this.fitAndEmitResize = fitAndEmitResize;
 
-    fitAndEmitResize(true);
+    fitAndEmitResize({ force: true, shouldClaim: false });
 
     const inputDisposable = terminal.onData((data) => {
       if (this.suppressInput) {
@@ -454,12 +457,12 @@ export class TerminalEmulatorRuntime {
       terminal,
     });
     const resizeObserver = new ResizeObserver(() => {
-      fitAndEmitResize(false);
+      fitAndEmitResize({ shouldClaim: true });
     });
     resizeObserver.observe(input.root);
     resizeObserver.observe(input.host);
 
-    const windowResizeHandler = () => fitAndEmitResize(false);
+    const windowResizeHandler = () => fitAndEmitResize({ shouldClaim: true });
     window.addEventListener("resize", windowResizeHandler);
     const windowFocusHandler = () => {
       this.handleVisibilityRestore();
@@ -472,26 +475,23 @@ export class TerminalEmulatorRuntime {
     document.addEventListener("visibilitychange", documentVisibilityChangeHandler);
 
     const visualViewport = window.visualViewport;
-    const visualViewportResizeHandler = () => fitAndEmitResize(false);
+    const visualViewportResizeHandler = () => fitAndEmitResize({ shouldClaim: true });
     visualViewport?.addEventListener("resize", visualViewportResizeHandler);
 
-    const fitInterval = window.setInterval(() => {
-      fitAndEmitResize(false);
-    }, 250);
     const fitTimeouts = FIT_TIMEOUT_DELAYS_MS.map((delayMs) =>
       window.setTimeout(() => {
-        fitAndEmitResize(true);
+        fitAndEmitResize({ force: true, shouldClaim: false });
       }, delayMs),
     );
 
     const fontSet = document.fonts;
     const fontReadyHandler = () => {
-      fitAndEmitResize(true);
+      fitAndEmitResize({ force: true, shouldClaim: false });
     };
     fontSet?.addEventListener?.("loadingdone", fontReadyHandler);
     void fontSet?.ready
       .then(() => {
-        fitAndEmitResize(true);
+        fitAndEmitResize({ force: true, shouldClaim: false });
         return;
       })
       .catch(() => {
@@ -499,7 +499,7 @@ export class TerminalEmulatorRuntime {
       });
 
     window.setTimeout(() => {
-      fitAndEmitResize(true);
+      fitAndEmitResize({ force: true, shouldClaim: false });
     }, 0);
 
     if (input.initialSnapshot) {
@@ -527,9 +527,6 @@ export class TerminalEmulatorRuntime {
       removeVisualViewportResize: () => {
         visualViewport?.removeEventListener("resize", visualViewportResizeHandler);
       },
-      clearFitInterval: () => {
-        window.clearInterval(fitInterval);
-      },
       clearFitTimeouts: () => {
         for (const handle of fitTimeouts) {
           window.clearTimeout(handle);
@@ -565,7 +562,6 @@ export class TerminalEmulatorRuntime {
       disposables.removeWindowFocus();
       disposables.removeDocumentVisibilityChange();
       disposables.removeVisualViewportResize();
-      disposables.clearFitInterval();
       disposables.clearFitTimeouts();
       disposables.removeFontListeners();
       disposables.removeTouchListeners();
@@ -635,8 +631,8 @@ export class TerminalEmulatorRuntime {
     this.processOutputQueue();
   }
 
-  resize(input?: { force?: boolean }): void {
-    this.fitAndEmitResize?.(input?.force ?? false);
+  resize(input?: { force?: boolean; shouldClaim?: boolean }): void {
+    this.fitAndEmitResize?.(input);
   }
 
   setTheme(input: { theme: ITheme }): void {

packages/app/src/terminal/webview/terminal-emulator-webview-entry.ts

@@ -30,7 +30,7 @@ type InboundMessage =
   | { type: "renderSnapshot"; streamKey: string; state: TerminalState | null }
   | { type: "clear"; streamKey: string }
   | { type: "focus"; streamKey: string; forceRefocus?: boolean }
-  | { type: "resize"; streamKey: string }
+  | { type: "resize"; streamKey: string; shouldClaim?: boolean }
   | { type: "setTheme"; streamKey: string; theme: ITheme }
   | { type: "setScrollback"; streamKey: string; lines: number }
   | { type: "setPendingModifiers"; streamKey: string; pendingModifiers: PendingTerminalModifiers }
@@ -46,7 +46,7 @@ type OutboundMessage =
   | { type: "bridgeReady" }
   | { type: "rendererReady"; streamKey: string; isReady: boolean }
   | { type: "input"; streamKey: string; data: string }
-  | { type: "resize"; streamKey: string; rows: number; cols: number }
+  | { type: "resize"; streamKey: string; rows: number; cols: number; shouldClaim?: boolean }
   | {
       type: "terminalKey";
       streamKey: string;
@@ -244,7 +244,7 @@ class TerminalWebViewBridge {
         this.runtime?.focus({ forceRefocus: message.forceRefocus });
         break;
       case "resize":
-        this.runtime?.resize({ force: true });
+        this.runtime?.resize({ force: true, shouldClaim: message.shouldClaim !== false });
         break;
       case "setTheme":
         this.applyThemeBackground(message.theme);
@@ -273,8 +273,8 @@ class TerminalWebViewBridge {
     runtime.setCallbacks({
       callbacks: {
         onInput: (data) => sendToNative({ type: "input", streamKey: message.streamKey, data }),
-        onResize: ({ rows, cols }) =>
-          sendToNative({ type: "resize", streamKey: message.streamKey, rows, cols }),
+        onResize: ({ rows, cols, shouldClaim }) =>
+          sendToNative({ type: "resize", streamKey: message.streamKey, rows, cols, shouldClaim }),
         onTerminalKey: (input) =>
           sendToNative({ type: "terminalKey", streamKey: message.streamKey, ...input }),
         onPendingModifiersConsumed: () =>