diff --git a/packages/runtime-tests/integration/lifecycle/mount-throw-teardown.sequential.test.tsx b/packages/runtime-tests/integration/lifecycle/mount-throw-teardown.sequential.test.tsx
new file mode 100644
index 0000000..687e3aa
--- /dev/null
+++ b/packages/runtime-tests/integration/lifecycle/mount-throw-teardown.sequential.test.tsx
@@ -0,0 +1,159 @@
+// Sequential: asserts on the process-global live yoga-node count
+// (yogaNodeTracker), which concurrent siblings that mount/unmount apps would
+// perturb. Tests are it.sequential.
+//
+// Bug: a SYNCHRONOUS throw during mount() BEFORE the originalMount try/catch
+// (e.g. stdin.setRawMode raising ERR_TTY_INIT_FAILED on a broken PTY, or kitty
+// enable's stdout.write throwing) skipped teardown(). liveInstances kept the
+// entry forever (poisoning the stdout: every later mount() hit the reuse guard
+// and no-op'd), the yoga root leaked, and raw mode was left on.
+
+import { PassThrough } from "node:stream";
+import { defineComponent } from "vue";
+import { expect, test, vi, afterEach } from "vite-plus/test";
+import { createApp, Text } from "@vue-tui/runtime";
+import { yogaNodeTracker } from "@vue-tui/runtime/internal";
+import { captureWrites, makeFakeWritable, makeFakeStdin } from "./test-streams.ts";
+
+afterEach(() => {
+  vi.restoreAllMocks();
+});
+
+/** Spy on native process.stderr (where the reuse-guard warning is written). */
+function spyOnGuardWarnings(): { warnings: string[]; restore: () => void } {
+  const warnings: string[] = [];
+  const spy = vi.spyOn(process.stderr, "write").mockImplementation((chunk) => {
+    warnings.push(typeof chunk === "string" ? chunk : String(chunk));
+    return true;
+  });
+  return { warnings, restore: () => spy.mockRestore() };
+}
+
+const GUARD_WARNING = "this stdout already has a live app";
+
+test.sequential("a synchronous setRawMode throw during mount() runs teardown: rethrows + does not poison the stdout", async () => {
+  yogaNodeTracker.reset();
+  const liveBefore = yogaNodeTracker.snapshot().live;
+
+  const App = defineComponent(() => () => <Text>hello</Text>);
+
+  const stdout = makeFakeWritable();
+  const stderr = makeFakeWritable();
+
+  // A TTY stdin whose setRawMode throws — simulates Node's
+  // ERR_TTY_INIT_FAILED on an SSH/container PTY that reports isTTY=true.
+  const { stream: stdin } = makeFakeStdin();
+  const ttyError = new Error("ERR_TTY_INIT_FAILED");
+  (stdin as unknown as { setRawMode: (m: boolean) => unknown }).setRawMode = () => {
+    throw ttyError;
+  };
+
+  const { restore } = spyOnGuardWarnings();
+
+  // (1) mount() must rethrow the injected error (the caller still sees it).
+  // rawMode defaults to "always" + interactive (TTY stdout) → the App acquires
+  // a lifetime raw-mode hold, which calls the throwing setRawMode.
+  const app1 = createApp(App);
+  expect(() => app1.mount({ stdout, stdin, stderr, interactive: true })).toThrow(
+    "ERR_TTY_INIT_FAILED",
+  );
+
+  // (2) The stdout is NOT poisoned: a subsequent mount() on the SAME stdout
+  // succeeds and renders, proving liveInstances was cleaned up by teardown()
+  // (before the fix this warned + no-op'd). Use a stdin that does NOT throw.
+  const { stream: stdin2 } = makeFakeStdin();
+  const writes = captureWrites(stdout);
+  const app2 = createApp(App);
+  app2.mount({ stdout, stdin: stdin2, stderr, debug: true, exitOnCtrlC: false });
+  await app2.waitUntilRenderFlush();
+
+  restore();
+  expect(writes.join("")).toContain("hello");
+
+  app2.unmount();
+
+  // (3) The yoga root allocated during the failed mount was freed (no leak):
+  // after the successful second app unmounts, live count is back to baseline.
+  expect(yogaNodeTracker.snapshot().live).toBe(liveBefore);
+});
+
+test.sequential("a synchronous stdout.write throw during kitty enable runs teardown (no poison)", async () => {
+  const App = defineComponent(() => () => <Text>kitty</Text>);
+
+  // A stdout whose write throws once kitty tries to enable the protocol.
+  const stdout = makeFakeWritable();
+  const enableError = new Error("BROKEN_STREAM_ON_KITTY_ENABLE");
+  const originalWrite = stdout.write.bind(stdout);
+  stdout.write = ((...args: unknown[]) => {
+    const chunk = String(args[0]);
+    // Kitty enable writes the push-flags CSI ("\x1b[>...u"); throw only on it.
+    if (chunk.includes("\x1b[>")) throw enableError;
+    return (originalWrite as Function)(...args);
+  }) as NodeJS.WriteStream["write"];
+
+  const stderr = makeFakeWritable();
+  const { stream: stdin } = makeFakeStdin();
+  const { warnings, restore } = spyOnGuardWarnings();
+
+  // (1) mount() rethrows the kitty-enable error.
+  const app1 = createApp(App);
+  expect(() =>
+    app1.mount({
+      stdout,
+      stdin,
+      stderr,
+      interactive: true,
+      kittyKeyboard: { mode: "enabled" },
+    }),
+  ).toThrow("BROKEN_STREAM_ON_KITTY_ENABLE");
+
+  // (2) Not poisoned: a fresh mount on the same stdout must NOT warn (the
+  // registry entry was evicted by teardown). Repair the stream first.
+  stdout.write = originalWrite as NodeJS.WriteStream["write"];
+  const { stream: stdin2 } = makeFakeStdin();
+  const app2 = createApp(App);
+  app2.mount({ stdout, stdin: stdin2, stderr, debug: true, exitOnCtrlC: false });
+  expect(warnings.join("")).not.toContain(GUARD_WARNING);
+  restore();
+  app2.unmount();
+});
+
+test.sequential("a throw AFTER attachYoga (during setWidth) still frees the yoga root", async () => {
+  // Targets the `mountedRoot = tuiRoot` ordering: attachYoga() has already
+  // allocated the root's yoga node, and setWidth(resolveSize(stdout).columns)
+  // throws. Recording mountedRoot BEFORE setWidth lets teardown's
+  // `if (mountedRoot) detachYoga(mountedRoot)` free that node.
+  yogaNodeTracker.reset();
+  const liveBefore = yogaNodeTracker.snapshot().live;
+
+  const App = defineComponent(() => () => <Text>after-attach</Text>);
+
+  // A TTY stdout whose `columns` getter throws — resolveSize() reads it to
+  // produce the setWidth() argument, so setWidth throws AFTER attachYoga ran.
+  const stdout = new PassThrough() as unknown as NodeJS.WriteStream;
+  const sizeError = new Error("COLUMNS_READ_FAILED");
+  Object.defineProperty(stdout, "columns", {
+    get() {
+      throw sizeError;
+    },
+  });
+  Object.assign(stdout, { rows: 100, isTTY: true });
+
+  const stderr = makeFakeWritable();
+  const { stream: stdin } = makeFakeStdin();
+  const { warnings, restore } = spyOnGuardWarnings();
+
+  // (1) mount() rethrows the setWidth error.
+  const app1 = createApp(App);
+  expect(() => app1.mount({ stdout, stdin, stderr, interactive: false })).toThrow(
+    "COLUMNS_READ_FAILED",
+  );
+
+  restore();
+
+  // (2) The yoga root allocated by attachYoga was freed (no leak): live count
+  // is back to baseline immediately after the failed mount.
+  expect(yogaNodeTracker.snapshot().live).toBe(liveBefore);
+  // No registry poison was introduced.
+  expect(warnings.join("")).not.toContain(GUARD_WARNING);
+});
diff --git a/packages/runtime/src/render.ts b/packages/runtime/src/render.ts
index 3b1d1c0..b5dffc9 100644
--- a/packages/runtime/src/render.ts
+++ b/packages/runtime/src/render.ts
@@ -767,27 +767,63 @@ export function createApp(root: Component, rootProps?: RootProps | null): TuiApp
     });
     mountedStdinController = stdinController;
 
-    // rawMode 'always': the App itself acquires a lifetime raw-mode ref now, so
-    // the refcount floor never drops to 0 while the app runs — raw mode is held
-    // continuously regardless of which input composables come and go, and there
-    // is no cooked-mode oscillation between input and no-input screens. Gated on
-    // interactive + isRawModeSupported (a TTY stdin): a non-interactive/piped run
-    // must not seize raw mode. The matching release happens in the controller's
-    // dispose() at teardown. (Diverges from Ink's lazy default — see
-    // .agents/docs/ink-divergences.md.)
-    if (rawMode === "always" && interactive && stdinController.isRawModeSupported) {
-      stdinController.holdRawModeForLifetime();
+    // These pre-mount steps can throw SYNCHRONOUSLY on a hostile/broken
+    // terminal: holdRawModeForLifetime() → stdin.setRawMode(true) raises
+    // ERR_TTY_INIT_FAILED when the ioctl fails (real on some SSH/container PTYs
+    // that still report isTTY=true); kittyController.init() may stdout.write()
+    // to enable the protocol (throws on a broken stream); attachYoga() allocates
+    // a WASM yoga node. liveInstances.set(stdout, app) already ran above, so a
+    // throw HERE — before the originalMount try/catch and before the process-
+    // exit / signal-exit handlers are wired — would leak the registry entry
+    // (poisoning the stdout: every later mount() hits the reuse guard and
+    // no-ops), leak the yoga root, and leave raw mode / kitty on. Wrap these in
+    // the same teardown-then-rethrow guard as originalMount so teardown()
+    // (idempotent; safe at this early stage — it derives all cleanup from the
+    // wired state set so far) restores everything and frees the registry entry,
+    // while the caller still sees the original error.
+    let kittyController: ReturnType<typeof createKittyKeyboardController>;
+    let tuiRoot: ReturnType<typeof createRoot>;
+    try {
+      // rawMode 'always': the App itself acquires a lifetime raw-mode ref now, so
+      // the refcount floor never drops to 0 while the app runs — raw mode is held
+      // continuously regardless of which input composables come and go, and there
+      // is no cooked-mode oscillation between input and no-input screens. Gated on
+      // interactive + isRawModeSupported (a TTY stdin): a non-interactive/piped run
+      // must not seize raw mode. The matching release happens in the controller's
+      // dispose() at teardown. (Diverges from Ink's lazy default — see
+      // .agents/docs/ink-divergences.md.)
+      if (rawMode === "always" && interactive && stdinController.isRawModeSupported) {
+        stdinController.holdRawModeForLifetime();
+      }
+
+      kittyController = createKittyKeyboardController(stdin, stdout);
+      // Register BEFORE init(): in auto mode, init() installs a stdin 'data'
+      // listener + a 200ms detection timer and only THEN writes the support
+      // query ("\x1b[?u") — which can throw on a broken stream. Assigning
+      // mountedKittyController first lets teardown's dispose() (which calls
+      // cancelDetection: removes the listener, clears the timer) run on that
+      // throw, instead of leaking a dangling stdin listener until the timer fires.
+      mountedKittyController = kittyController;
+      kittyController.init(options.kittyKeyboard, interactive);
+
+      tuiRoot = createRoot(appContext);
+      attachYoga(tuiRoot);
+      // Record the root BEFORE setWidth so teardown's `if (mountedRoot)
+      // detachYoga(mountedRoot)` frees the just-allocated yoga node even if
+      // setWidth (or anything below) throws.
+      mountedRoot = tuiRoot;
+      tuiRoot.yoga.setWidth(resolveSize(stdout).columns);
+    } catch (err) {
+      try {
+        teardown(); // best-effort: free yoga, restore raw mode/kitty, evict registry entry
+      } catch {
+        // A failing best-effort restore must NOT replace `err` — the ORIGINAL
+        // pre-mount error must survive and be rethrown (mirrors the
+        // originalMount catch below).
+      }
+      throw err;
     }
 
-    const kittyController = createKittyKeyboardController(stdin, stdout);
-    kittyController.init(options.kittyKeyboard, interactive);
-    mountedKittyController = kittyController;
-
-    const tuiRoot = createRoot(appContext);
-    attachYoga(tuiRoot);
-    tuiRoot.yoga.setWidth(resolveSize(stdout).columns);
-    mountedRoot = tuiRoot;
-
     // Reset accumulated static output when the <Static> identity changes
     // (unmount, remount via key change) so stale items are not replayed.
     tuiRoot.onStaticChange = () => {