fix(runtime): guard writeToStdout/writeToStderr against post-teardown writes (Ink parity, G20) (#49)

* fix(runtime): guard writeToStdout/writeToStderr against post-teardown writes (Ink parity, G20)

Return early if teardownStarted, mirroring Ink ink.tsx:673/702, so a write
after unmount (e.g. a stray useStdout().write or console.log routed through
writeToStdout after teardown) cannot run clear()/write/restore on an
already-torn-down renderer and corrupt the restored terminal state.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* chore(parity): ledger — G20 pr-open, reconcile G19 merged

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

.agents/docs/parity-ledger.md

@@ -53,8 +53,8 @@ Non-obvious calls made while fixing gaps, recorded for review in the final repor
 | G16 | box-layout-border               | Per-edge borderDimColor=false cannot override general borderDimColor (`\|\| dimAll` vs Ink's `??`)                                                                                  | P3       | merged    | `fix/parity-border-dim`            | #44 |
 | G17 | render-lifecycle-reconciler     | Screen-reader live-path edges: <Static> still grid-painted (Ink linearizes, skipStaticElements:false) + empty SR frame gets a trailing newline (Ink writes wrapped output directly) | P3       | merged    | `fix/parity-sr-edges`              | #45 |
 | G18 | render-lifecycle-reconciler     | No signal-based teardown — terminal corrupted on SIGINT/SIGTERM/SIGHUP (Ink signal-exit at mount)                                                                                   | P1       | merged    | `fix/parity-signal-teardown`       | #47 |
-| G19 | box-layout-border               | Dynamic removal of most yoga style props does not reset to default (stale layout)                                                                                                   | P2       | pr-open   | `fix/parity-yoga-reset`            | #48 |
+| G19 | box-layout-border               | Dynamic removal of most yoga style props does not reset to default (stale layout)                                                                                                   | P2       | merged    | `fix/parity-yoga-reset`            | #48 |
-| G20 | stdout-stderr-stdin-size-cursor | writeToStdout/writeToStderr lack an isUnmounted/teardown guard (post-teardown writes corrupt terminal)                                                                              | P2       | todo      | —                                  | —   |
+| G20 | stdout-stderr-stdin-size-cursor | writeToStdout/writeToStderr lack an isUnmounted/teardown guard (post-teardown writes corrupt terminal)                                                                              | P2       | pr-open   | `fix/parity-write-after-unmount`   | #49 |
 | G21 | text-wrap-transform             | Nested <Transform> in <Text> gets hardcoded index 0 vs child sibling position (squash path)                                                                                         | P3       | todo      | —                                  | —   |
 | G22 | app-exit-instances-animation-sr | SR role dedup inherits grandparent role; Ink dedups only vs immediate parent                                                                                                        | P3       | todo      | —                                  | —   |
 | G23 | app-exit-instances-animation-sr | <Transform> under <Box> SR-joins children with newline; Ink concatenates                                                                                                            | P3       | todo      | —                                  | —   |

packages/runtime-tests/integration/composables/write-after-unmount.test.tsx

@@ -0,0 +1,116 @@
+/**
+ * G20 — writeToStdout/writeToStderr must no-op after teardown (Ink parity).
+ *
+ * Ink ink.tsx:673/702 returns early when the instance is unmounted so that a
+ * write after teardown cannot run clear()/write/restore on an already-torn-down
+ * renderer and corrupt the terminal.  vue-tui must mirror that guard.
+ */
+import { PassThrough } from "node:stream";
+import { defineComponent } from "vue";
+import { expect, test } from "vite-plus/test";
+import { createApp, Text, useStdout, useStderr } from "@vue-tui/runtime";
+
+function makeTtyStream(): NodeJS.WriteStream & { chunks: string[] } {
+  const s = new PassThrough() as unknown as NodeJS.WriteStream & { chunks: string[] };
+  Object.assign(s, { columns: 80, rows: 24, isTTY: true, chunks: [] as string[] });
+  s.on("data", (chunk: Buffer) => s.chunks.push(chunk.toString()));
+  return s;
+}
+
+function makeFakeStdin(): NodeJS.ReadStream {
+  const s = new PassThrough() as unknown as NodeJS.ReadStream;
+  Object.assign(s, {
+    isTTY: true,
+    setRawMode() {
+      return s;
+    },
+    setEncoding() {
+      return s;
+    },
+  });
+  (s as any).ref = () => {};
+  (s as any).unref = () => {};
+  return s;
+}
+
+test("writeToStdout: pre-unmount write works, post-unmount write is suppressed", async () => {
+  const stdout = makeTtyStream();
+  const stderr = makeTtyStream();
+  const stdin = makeFakeStdin();
+
+  let writeRef: ((data: string) => void) | undefined;
+
+  const App = defineComponent(() => {
+    const { write } = useStdout();
+    writeRef = write;
+    return () => <Text>frame</Text>;
+  });
+
+  const app = createApp(App);
+  app.mount({ stdout, stdin, stderr, debug: false, exitOnCtrlC: false });
+
+  // Wait for initial render to settle
+  await new Promise<void>((r) => setTimeout(r, 60));
+
+  // Control: a write BEFORE unmount should produce output
+  stdout.chunks.length = 0;
+  writeRef!("before-unmount\n");
+  const beforeChunks = stdout.chunks.join("");
+  expect(beforeChunks, "pre-unmount write must produce output").toContain("before-unmount");
+
+  // Now unmount (triggers teardown)
+  app.unmount();
+
+  // Clear captured chunks and attempt a write AFTER unmount
+  stdout.chunks.length = 0;
+  writeRef!("after-unmount\n");
+  const afterChunks = stdout.chunks.join("");
+
+  // The guard must prevent any write to stdout after teardown
+  expect(
+    afterChunks,
+    `post-unmount write must be suppressed; got: ${JSON.stringify(afterChunks)}`,
+  ).not.toContain("after-unmount");
+});
+
+test("writeToStderr: pre-unmount write works, post-unmount write is suppressed", async () => {
+  const stdout = makeTtyStream();
+  const stderr = makeTtyStream();
+  const stdin = makeFakeStdin();
+
+  let writeRef: ((data: string) => void) | undefined;
+
+  const App = defineComponent(() => {
+    const { write } = useStderr();
+    writeRef = write;
+    return () => <Text>frame</Text>;
+  });
+
+  const app = createApp(App);
+  app.mount({ stdout, stdin, stderr, debug: false, exitOnCtrlC: false });
+
+  // Wait for initial render to settle
+  await new Promise<void>((r) => setTimeout(r, 60));
+
+  // Control: a write BEFORE unmount should produce output on stderr
+  stderr.chunks.length = 0;
+  writeRef!("before-unmount-err\n");
+  const beforeChunks = stderr.chunks.join("");
+  expect(beforeChunks, "pre-unmount stderr write must produce output").toContain(
+    "before-unmount-err",
+  );
+
+  // Now unmount (triggers teardown)
+  app.unmount();
+
+  // Clear captured chunks and attempt a write AFTER unmount
+  stderr.chunks.length = 0;
+  writeRef!("after-unmount-err\n");
+  const afterChunks = stderr.chunks.join("");
+
+  // The guard must prevent any write to stderr after teardown
+  expect(
+    afterChunks,
+    `post-unmount stderr write must be suppressed; got: ${JSON.stringify(afterChunks)}`,
+  ).not.toContain("after-unmount-err");
+});

packages/runtime/src/render.ts

@@ -481,6 +481,10 @@ export function createApp(root: Component, rootProps?: RootProps | null): TuiApp
     }
 
     function writeToStdout(data: string) {
+      // Mirror Ink ink.tsx:673: return early after teardown so a late write
+      // (e.g. a stray useStdout().write after unmount) cannot run
+      // clear()/write/restore on an already-torn-down renderer.
+      if (teardownStarted) return;
       if (debug) {
         stdout.write(data + frameState.fullStaticOutput + frameState.lastOutput);
         return;
@@ -500,6 +504,9 @@ export function createApp(root: Component, rootProps?: RootProps | null): TuiApp
     }
 
     function writeToStderr(data: string) {
+      // Mirror Ink ink.tsx:702: return early after teardown so a late write
+      // cannot corrupt the restored terminal state.
+      if (teardownStarted) return;
       if (debug) {
         stderr.write(data);
         stdout.write(frameState.fullStaticOutput + frameState.lastOutput);