fix: harden web terminal paste and reconnect

- Queue bounded ordered terminal input so acknowledgements remain responsive
- Prevent stale sockets and retries from replacing healthy connections
- Preserve desktop scrollback behavior and add terminal regression coverage

Quality gates: frontend tests (91 passed), typecheck, lint, build, Python compilation, LSP diagnostics. Backend pytest skipped by user request.

apps/web/src/components/features/terminal/terminal.test.ts

@@ -1,6 +1,10 @@
 import { describe, expect, it } from "vitest";
 
-import { getTerminalScrollbackLimit } from "./terminal.tsx";
+import {
+	getTerminalScrollbackLimit,
+	isCurrentWebSocket,
+	shouldRetryWebSocketClose,
+} from "./terminal.tsx";
 
 describe("getTerminalScrollbackLimit", () => {
 	it("retains normal-buffer history for custom mobile swipe scrolling", () => {
@@ -10,4 +14,19 @@ describe("getTerminalScrollbackLimit", () => {
 	it("keeps desktop scrollback disabled to prevent stale-frame wheel scrolling", () => {
 		expect(getTerminalScrollbackLimit(false)).toBe(0);
 	});
+
+	it("rejects stale WebSocket callbacks after a replacement connection", () => {
+		const current = {} as WebSocket;
+		const stale = {} as WebSocket;
+
+		expect(isCurrentWebSocket(current, current)).toBe(true);
+		expect(isCurrentWebSocket(current, stale)).toBe(false);
+	});
+
+	it("retries a heartbeat timeout but not a server socket replacement", () => {
+		expect(shouldRetryWebSocketClose(4000, "Heartbeat timeout")).toBe(true);
+		expect(shouldRetryWebSocketClose(4000, "New connection established")).toBe(
+			false,
+		);
+	});
 });