diff --git a/packages/ai/test/remote-auth-store.test.ts b/packages/ai/test/remote-auth-store.test.ts
index 56b203664..d730efce7 100644
--- a/packages/ai/test/remote-auth-store.test.ts
+++ b/packages/ai/test/remote-auth-store.test.ts
@@ -1110,7 +1110,7 @@ describe("RemoteAuthCredentialStore + AuthStorage integration", () => {
 
 	test("broker invalidation drops server-side last-good usage reports", async () => {
 		const credential = serverStore!.listAuthCredentials("anthropic")[0];
-		if (!credential || credential.credential.type !== "oauth") throw new Error("expected OAuth credential");
+		if (credential?.credential.type !== "oauth") throw new Error("expected OAuth credential");
 		serverStore!.updateAuthCredential(credential.id, {
 			...credential.credential,
 			expires: Date.now() + 3_600_000,
diff --git a/packages/tui/CHANGELOG.md b/packages/tui/CHANGELOG.md
index 67107570e..0414a5349 100644
--- a/packages/tui/CHANGELOG.md
+++ b/packages/tui/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed a terminal Device-Attributes reply leaking into the composer as literal text (e.g. `1;22;…;52c`) when it arrived after the startup capability-probe sentinel FIFO drained, a race made observable by the added latency of an SSH/zmx PTY chain. DA1 replies (`CSI ? … c`) and split private-CSI responses are now consumed for the whole session lifetime, not only while a probe sentinel is outstanding ([#8542](https://github.com/can1357/oh-my-pi/issues/8542)).
+
 ## [17.3.3] - 2026-08-14
 
 ### Fixed
diff --git a/packages/tui/src/terminal.ts b/packages/tui/src/terminal.ts
index 537123db2..36d0f1170 100644
--- a/packages/tui/src/terminal.ts
+++ b/packages/tui/src/terminal.ts
@@ -945,10 +945,11 @@ export class ProcessTerminal implements Terminal {
 			// flush timeout elapses mid-sequence, the prefix `\x1b[?<digits>` arrives as
 			// one event and the tail `;...<terminator>` arrives as individual character
 			// events that would otherwise leak into the prompt as keystrokes. See #1238.
-			if (
-				this.#privateCsiResponseBuffer ||
-				(privateCsiPartialPattern.test(sequence) && this.#da1SentinelOwners.length > 0)
-			) {
+			// A private CSI (`\x1b[?…`) is a terminal->host report, never a keystroke, so
+			// reassembly stays armed for the whole session — not just while a probe
+			// sentinel is outstanding — otherwise a reply that lands after the sentinel
+			// FIFO drains (slow SSH/PTY links) leaks its tail into the composer (#8542).
+			if (this.#privateCsiResponseBuffer || privateCsiPartialPattern.test(sequence)) {
 				if (this.#privateCsiResponseBuffer && sequence.startsWith("\x1b")) {
 					// New escape arrived mid-reassembly — abandon partial and re-process the new sequence.
 					this.#privateCsiResponseBuffer = "";
@@ -1038,10 +1039,16 @@ export class ProcessTerminal implements Terminal {
 			}
 
 			// DA1 response: swallow our sentinel reply regardless of whether an
-			// earlier capability-specific response already succeeded. Other terminal
-			// probes should never see these replies.
-			if (da1ResponsePattern.test(sequence) && this.#da1SentinelOwners.length > 0) {
-				const owner = this.#da1SentinelOwners.shift()!;
+			// earlier capability-specific response already succeeded. `CSI ? … c` is
+			// exclusively a terminal->host report, so it is swallowed even with no
+			// outstanding sentinel — a reply that arrives after the FIFO drains (slow
+			// SSH/PTY links) must never reach the composer as literal text (#8542).
+			if (da1ResponsePattern.test(sequence)) {
+				const owner = this.#da1SentinelOwners.shift();
+				if (!owner) {
+					// Late/unowned reply: nothing to resolve, just drop the bytes.
+					return;
+				}
 				switch (owner.kind) {
 					case "osc11": {
 						if (this.#osc11Pending) {
diff --git a/packages/tui/test/issue-8542-repro.test.ts b/packages/tui/test/issue-8542-repro.test.ts
new file mode 100644
index 000000000..f0db7ed64
--- /dev/null
+++ b/packages/tui/test/issue-8542-repro.test.ts
@@ -0,0 +1,88 @@
+import { afterEach, describe, expect, it, vi } from "bun:test";
+import { ProcessTerminal } from "@oh-my-pi/pi-tui/terminal";
+import { setTerminalHeadless } from "@oh-my-pi/pi-utils";
+
+// #8542: a terminal Device-Attributes reply to omp's startup capability probe
+// leaks into the composer as literal text (`1;22;...;52c`) when it arrives
+// after the DA1 sentinel FIFO has already drained. The extra SSH+zmx PTY hops
+// slow the query->response round-trip enough to make the race observable.
+//
+// Contract: `CSI ? … c` is exclusively a terminal->host report, never a
+// keystroke, so it MUST be consumed for the whole session lifetime and never
+// forwarded to the input handler that feeds the composer.
+
+// A meaty multi-parameter DA1 reply, exactly as the reporter observed it.
+const DA1_REPLY = "\x1b[?1;22;23;24;28;32;42;52c";
+
+describe("issue #8542: late DA response must not leak into the composer", () => {
+	let terminal: ProcessTerminal | undefined;
+	let previousHeadless = false;
+	let spies: Array<{ mockRestore(): void }> = [];
+	const captured: string[] = [];
+
+	function setup(): void {
+		previousHeadless = setTerminalHeadless(false);
+		Object.defineProperty(process.stdin, "isTTY", { value: true, configurable: true });
+		Object.defineProperty(process.stdout, "isTTY", { value: true, configurable: true });
+		Object.defineProperty(process.stdin, "setRawMode", { value: vi.fn(), configurable: true });
+		Object.defineProperty(process.stdout, "columns", { value: 100, configurable: true });
+		Object.defineProperty(process.stdout, "rows", { value: 30, configurable: true });
+		spies = [
+			vi.spyOn(process.stdin, "resume").mockImplementation(() => process.stdin),
+			vi.spyOn(process.stdin, "pause").mockImplementation(() => process.stdin),
+			vi.spyOn(process.stdin, "setEncoding").mockImplementation(() => process.stdin),
+			vi.spyOn(process.stdout, "write").mockImplementation(() => true),
+			vi.spyOn(process, "kill").mockImplementation(() => true),
+		];
+		captured.length = 0;
+		terminal = new ProcessTerminal();
+		terminal.start(
+			data => captured.push(data),
+			() => {},
+		);
+	}
+
+	afterEach(() => {
+		terminal?.stop();
+		terminal = undefined;
+		for (const spy of spies) spy.mockRestore();
+		spies = [];
+		Reflect.deleteProperty(process.stdin, "isTTY");
+		Reflect.deleteProperty(process.stdout, "isTTY");
+		Reflect.deleteProperty(process.stdin, "setRawMode");
+		Reflect.deleteProperty(process.stdout, "columns");
+		Reflect.deleteProperty(process.stdout, "rows");
+		setTerminalHeadless(previousHeadless);
+	});
+
+	it("swallows a single-event DA reply that arrives after the sentinel FIFO drains", () => {
+		setup();
+		// Complete `CSI ? … c` sequences flow through the StdinBuffer synchronously.
+		// Over-supply them: the first few resolve the startup probe sentinels, the
+		// rest model the slow SSH/PTY reply that lands with an empty FIFO. None may
+		// reach the composer.
+		for (let i = 0; i < 32; i++) process.stdin.emit("data", DA1_REPLY);
+
+		expect(captured.join("")).toBe("");
+	});
+
+	it("reassembles and swallows a split DA reply arriving with an empty FIFO", async () => {
+		setup();
+		// Drain the sentinel FIFO first (complete replies, processed synchronously).
+		for (let i = 0; i < 32; i++) process.stdin.emit("data", "\x1b[?62c");
+		captured.length = 0;
+
+		// The prefix of a slow reply arrives alone; the StdinBuffer holds it as an
+		// unambiguous private-CSI partial, then flushes it once its real timeout
+		// (<= PARTIAL_HOLD_MAX_MS = 150ms) elapses mid-sequence. This exercises the
+		// terminal-level reassembly path that only fires against the wall clock —
+		// deterministic fake timers cannot drive the StdinBuffer's internal flush
+		// here, so a genuine delay past the hold bound is required.
+		process.stdin.emit("data", "\x1b[?1;22;23");
+		await Bun.sleep(200);
+		// Tail bytes arrive as ordinary input after the flush.
+		process.stdin.emit("data", ";24;28;32;42;52c");
+
+		expect(captured.join("")).toBe("");
+	});
+});
diff --git a/packages/tui/test/terminal-appearance.test.ts b/packages/tui/test/terminal-appearance.test.ts
index 1cb6169fd..dcf828b7a 100644
--- a/packages/tui/test/terminal-appearance.test.ts
+++ b/packages/tui/test/terminal-appearance.test.ts
@@ -625,9 +625,12 @@ describe("ProcessTerminal OSC 11 appearance detection", () => {
 		process.stdin.emit("data", "\x1b[?1;2c");
 		expect(received).toEqual([]);
 
-		// An eighth stray DA1 has no owner and must reach the input handler — it is
+		// An eighth stray DA1 has no owner, yet is still swallowed: `CSI ? … c` is
+		// exclusively a terminal->host report, never a keystroke, so a reply that
+		// lands after the sentinel FIFO drains (slow SSH/PTY links) must not leak
+		// into the composer as literal text (#8542).
 		process.stdin.emit("data", "\x1b[?1;2c");
-		expect(received).toEqual(["\x1b[?1;2c"]);
+		expect(received).toEqual([]);
 
 		terminal.stop();
 	});