fix: suppress terminal query response leaks

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

@@ -24,6 +24,7 @@ interface MountedTerminal {
   host: HTMLDivElement;
   root: HTMLDivElement;
   runtime: TerminalEmulatorRuntime;
+  inputs: string[];
   sizes: TerminalSize[];
 }
 
@@ -65,9 +66,13 @@ function createTerminalHost(input: { width: number; height: number }): MountedTe
   document.body.appendChild(root);
 
   const sizes: TerminalSize[] = [];
+  const inputs: string[] = [];
   const runtime = new TerminalEmulatorRuntime();
   runtime.setCallbacks({
     callbacks: {
+      onInput: (data) => {
+        inputs.push(data);
+      },
       onResize: (size) => {
         sizes.push(size);
       },
@@ -84,7 +89,7 @@ function createTerminalHost(input: { width: number; height: number }): MountedTe
     },
   });
 
-  const mounted = { host, root, runtime, sizes };
+  const mounted = { host, root, runtime, inputs, sizes };
   mountedTerminals.push(mounted);
   return mounted;
 }
@@ -157,6 +162,22 @@ describe("terminal emulator runtime in a real browser", () => {
     expect(refreshCalls.at(-1)).toEqual([0, terminal.rows - 1]);
   });
 
+  it("suppresses non-identity terminal query responses as PTY input", async () => {
+    await page.viewport(900, 600);
+    const mounted = createTerminalHost({ width: 720, height: 360 });
+
+    await waitFor({ predicate: () => mounted.sizes.length > 0 });
+
+    const querySequences = ["\x1b[5n", "\x1b[6n", "\x1b[?6n", "\x1b[1$p", "\x1b[?1$p"];
+
+    for (const sequence of querySequences) {
+      mounted.runtime.write({ text: sequence });
+    }
+    await nextFrame();
+
+    expect(mounted.inputs).toEqual([]);
+  });
+
   it("replays snapshots without synchronously resetting the visible terminal", async () => {
     await page.viewport(900, 600);
     const mounted = createTerminalHost({ width: 720, height: 360 });

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

@@ -237,11 +237,14 @@ export class TerminalEmulatorRuntime {
       }
     });
 
-    // Suppress terminal query responses — the server-side headless xterm handles these.
-    // Without this, xterm.js generates DA/CPR responses via onData that feed back
-    // to the PTY as visible text.
-    terminal.parser.registerCsiHandler({ final: "c" }, () => true);
+    // Suppress cursor/status query responses whose async browser replies can race
+    // with foreground app exit and feed back to the shell as visible text. DA is
+    // intentionally left to xterm so attached TUIs can identify the terminal.
+    terminal.parser.registerCsiHandler({ final: "n" }, () => true);
+    terminal.parser.registerCsiHandler({ prefix: "?", final: "n" }, () => true);
     terminal.parser.registerCsiHandler({ final: "R" }, () => true);
+    terminal.parser.registerCsiHandler({ intermediates: "$", final: "p" }, () => true);
+    terminal.parser.registerCsiHandler({ prefix: "?", intermediates: "$", final: "p" }, () => true);
 
     const restoreDocumentStyles = this.applyDocumentBoundsStyles({
       root: input.root,

packages/server/src/terminal/terminal.test.ts

@@ -978,6 +978,23 @@ describe("subscribe", () => {
 
     expect(messages.length).toBe(0);
   });
+
+  it("does not answer terminal identity queries from the headless snapshot parser", async () => {
+    const session = trackSession(
+      await createTerminal({
+        cwd: "/tmp",
+        shell: "/bin/sh",
+        env: { PS1: "$ " },
+      }),
+    );
+
+    await waitForLines(session, ["$"]);
+
+    session.send({ type: "input", data: "printf '\\033[c'; echo after-da\r" });
+    await waitForState(session, (state) => getLines(state).join("\n").includes("after-da"));
+
+    expect(getLines(session.getState()).join("\n")).not.toContain("62;4;22c");
+  });
 });
 
 describe("stream snapshots", () => {

packages/server/src/terminal/terminal.ts

@@ -657,15 +657,6 @@ export async function createTerminal(options: CreateTerminalOptions): Promise<Te
   }
   emitTitleChange(initialTitle);
 
-  // Respond to DA1 queries (CSI c or CSI 0 c) — apps like nvim query terminal capabilities
-  terminal.parser.registerCsiHandler({ final: "c" }, (params) => {
-    if (params.length === 0 || (params.length === 1 && params[0] === 0)) {
-      ptyProcess.write("\x1b[?62;4;22c");
-      return true;
-    }
-    return false;
-  });
-
   let disposeTitleChangeSubscription: { dispose(): void } | null = null;
   if (!lockedTitle) {
     disposeTitleChangeSubscription = terminal.onTitleChange((nextTitle) => {