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fix(server): restore alt-screen mode on SCREEN replay (#49)
Track whether the child has entered the alternate screen buffer (DEC
private modes ?1049 / ?1047 / ?47) via a new altScreenActive flag on
PtyServer, and prepend \x1b[?1049h to the SCREEN packet payload sent
on ATTACH when the child is currently in alt-screen. PEEK does not
get the prefix — a non-follow peek prints its snapshot into the
caller's shell and exits, so entering alt-screen would hide the
output when the client's TERMINAL_SANITIZE (?1049l) fires on close.
Fixes #41. Before this, a full-screen TUI (vim/htop/codex) attached
through pty would paint into the host's main-screen buffer, which
under tmux meant every full repaint entered scrollback. Observed
impact: 8.7 GB scrollback + 9.1 GB tmux server RSS over 9.5h on a
long-lived codex pane, with 0.4-2.3s server-loop stalls.
The wire format is unchanged — the prefix rides on the existing SCREEN
payload as a strict superset. Old clients (pre-fix) receiving the
prefixed payload just write it verbatim to their terminal and enter
alt-screen correctly. Client-side detach already emits ?1049l via
TERMINAL_SANITIZE, so the round-trip is symmetric.
+164
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+3
CHANGELOG.md
+3
CHANGELOG.md
···
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## Unreleased
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### Fixes
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- **Alt-screen buffer mode is now restored on SCREEN replay.** The daemon tracks whether the child has entered the alternate screen buffer (DEC private modes `?1049`, `?1047`, `?47`) and prepends `\x1b[?1049h` to the SCREEN packet payload sent on ATTACH when the child is currently in alt-screen. Fixes #41 — before this, a full-screen TUI (vim/htop/codex) attached through `pty` would paint into the host's main-screen buffer, which under tmux meant every frame entered scrollback: an observed 8.7 GB scrollback / 9.1 GB tmux server RSS over 9.5h on a long-lived codex pane. The client-side detach path already resets `?1049l` via `TERMINAL_SANITIZE`, so the round-trip is symmetric. PEEK does not get the prefix — a non-follow peek prints its snapshot into the caller's shell and immediately exits, so entering alt-screen would hide the output when TERMINAL_SANITIZE fires on close.
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### Breaking changes — supervisor replaced by `pty gc`
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- **Removed the long-running `pty supervisor` command and the launchd FDA wrapper.** All `pty supervisor *` subcommands are gone (`start`, `stop`, `status`, `forget`, `reset`, `launchd install/uninstall`, `systemd install/uninstall`, `runit install/uninstall`). The bundled `src/supervisor.ts`, `src/supervisor-entry.ts`, and `scripts/supervisor-wrapper.c` are deleted. So are the three supervisor test files (`tests/supervisor.test.ts`, `tests/supervisor-hardening.test.ts`, `tests/supervisor-service-install.test.ts`). Net: about 600 lines of code and a separate long-lived process removed.
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- **`pty gc` now does the supervisor's work**, statelessly, as a one-shot reconciliation pass. Every invocation re-derives intent from on-disk metadata; there's no in-memory restart counter, no persisted bookkeeping, no backoff state, no `[failed]` mark. Three steps run in order on each call: (1) walk sessions with a `parent=<name>` tag and SIGTERM + clean up any whose parent is gone; (2) respawn every `strategy=permanent` session that's exited or vanished (re-reading `pty.toml` when the session is toml-managed); (3) sweep exited/vanished non-permanent sessions (the historic `pty gc` behavior). The intended deployment is to run it on a short cron (default 30 s); failures (binary not on PATH, volume not mounted at boot) are non-events because the next tick tries again. This fixes the boot-time mount race where a supervised session under `/Volumes/SSD` would exhaust its 5-retry budget within 10 s of launchd firing before the volume even mounted.
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src/server.ts
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src/server.ts
···
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private sgrMouseMode = false;
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private cursorHidden = false;
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private kittyKeyboardStack: number[] = [];
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// Alt-screen buffer state (DEC private modes ?1049 / ?1047 / ?47). Set when
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// the child process enters the alternate screen buffer; cleared when it
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// leaves. Replayed to attaching clients so the SCREEN snapshot lands in the
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// right host-terminal buffer — without this, a TUI's alt-screen frames get
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// painted into the host's main buffer, which under tmux means every frame
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// enters scrollback (see #41).
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private altScreenActive = false;
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// Mouse tracking modes — these are separate DEC private modes (set/cleared
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// independently by the child process) that control WHICH events the
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// terminal should report. SGR mode (1006) only controls the ENCODING of
···
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if (v === 1000) this.mouseTracking1000 = true;
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if (v === 1002) this.mouseTracking1002 = true;
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if (v === 1003) this.mouseTracking1003 = true;
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if (v === 1049 || v === 1047 || v === 47) this.altScreenActive = true;
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if (v === 25) {
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if (this.cursorHidden) this.emitEvent(EventType.CURSOR_VISIBLE);
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this.cursorHidden = false;
···
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if (v === 1000) this.mouseTracking1000 = false;
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if (v === 1002) this.mouseTracking1002 = false;
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if (v === 1003) this.mouseTracking1003 = false;
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if (v === 1049 || v === 1047 || v === 47) this.altScreenActive = false;
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if (v === 25) this.cursorHidden = true;
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}
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return false;
···
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const sendScreen = () => {
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if (socket.destroyed) return;
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const screen = this.getModePrefix() + this.serialize.serialize();
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const screen = this.getModePrefix(true) + this.serialize.serialize();
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socket.write(encodeScreen(screen));
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if (this.exited) {
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socket.write(encodeExit(this.exitCode));
···
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});
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}
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private getModePrefix(): string {
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private getModePrefix(includeAltScreen = false): string {
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let prefix = "";
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// Alt-screen mode is only prefixed for the ATTACH path, not PEEK. A
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// non-follow `pty peek` prints the snapshot to the caller's shell and
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// exits, so entering ?1049h would hide the output when the client-side
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// TERMINAL_SANITIZE exits alt-screen on close. Attaching clients want
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// the alt buffer to persist for the duration of the attach.
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if (includeAltScreen && this.altScreenActive) prefix += "\x1b[?1049h";
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if (this.mouseTracking1000) prefix += "\x1b[?1000h";
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if (this.mouseTracking1002) prefix += "\x1b[?1002h";
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if (this.mouseTracking1003) prefix += "\x1b[?1003h";
+144
tests/screen-replay-altscreen.test.ts
+144
tests/screen-replay-altscreen.test.ts
···
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import { describe, it, expect, afterAll } from "vitest";
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import * as net from "node:net";
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import * as fs from "node:fs";
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import * as os from "node:os";
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import { Session } from "../src/testing/index.ts";
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import {
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MessageType,
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PacketReader,
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encodeAttach,
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encodePeek,
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} from "../src/protocol.ts";
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import { getSocketPath } from "../src/sessions.ts";
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// Isolate from real session directory.
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const testSessionDir = fs.mkdtempSync(os.tmpdir() + "/pty-altscreen-");
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process.env.PTY_SESSION_DIR = testSessionDir;
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afterAll(() => {
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return new Promise((resolve) => {
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setTimeout(() => {
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try { fs.rmSync(testSessionDir, { recursive: true, force: true }); } catch {}
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resolve(undefined);
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}, 500);
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});
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});
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// Capture the raw SCREEN payload sent in response to `packet` on a fresh
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// socket to `session`. Returns the payload string. Waits up to 3s.
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async function captureScreen(sessionName: string, requestPacket: Buffer): Promise<string> {
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const sock = net.createConnection(getSocketPath(sessionName));
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const reader = new PacketReader();
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try {
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await new Promise<void>((resolve, reject) => {
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sock.once("connect", () => resolve());
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sock.once("error", reject);
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});
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const payload = await new Promise<string>((resolve, reject) => {
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const timer = setTimeout(() => reject(new Error("timeout waiting for SCREEN")), 3000);
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sock.on("data", (data: Buffer) => {
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let packets;
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try { packets = reader.feed(data); } catch (err: any) {
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clearTimeout(timer);
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reject(err);
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return;
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}
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for (const p of packets) {
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if (p.type === MessageType.SCREEN) {
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clearTimeout(timer);
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resolve(p.payload.toString());
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return;
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}
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}
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});
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sock.write(requestPacket);
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});
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return payload;
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} finally {
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sock.destroy();
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}
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}
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describe("SCREEN replay carries alt-screen mode", () => {
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it("ATTACH prefixes ?1049h at position 0 when child is in the alternate screen buffer", async () => {
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// Child enters alt-screen, writes a marker, then blocks.
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const session = await Session.server(
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"sh",
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["-c", "printf '\\033[?1049h\\033[Halt-marker'; sleep 60"],
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{ rows: 24, cols: 80 },
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);
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// Wait for the daemon's xterm-headless to process the ?1049h and content.
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await new Promise((r) => setTimeout(r, 300));
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const screen = await captureScreen(session.name, encodeAttach(24, 80));
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// The alt-screen enter mode must be the very first bytes so the client's
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// real terminal switches buffers before any content is painted. Position
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// 0 is a stronger check than "contains" because xterm-addon-serialize may
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// independently emit `?1049h` mid-payload; this asserts the guarantee THIS
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// patch adds — the mode is set at the start, deterministically.
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expect(screen.startsWith("\x1b[?1049h")).toBe(true);
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expect(screen).toContain("alt-marker");
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await session.close();
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}, 15000);
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it("ATTACH does not prefix ?1049h when child is in the main screen buffer", async () => {
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const session = await Session.server(
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"sh",
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["-c", "printf 'main-only'; sleep 60"],
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{ rows: 24, cols: 80 },
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);
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await new Promise((r) => setTimeout(r, 300));
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const screen = await captureScreen(session.name, encodeAttach(24, 80));
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// The prefix guarantee is position-0. Main-screen sessions must not have
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// ?1049h at the start (would poison the client's host terminal).
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expect(screen.startsWith("\x1b[?1049h")).toBe(false);
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await session.close();
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}, 15000);
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it("ATTACH stops prefixing ?1049h after child exits alt-screen", async () => {
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// Child enters and immediately exits alt-screen, then writes to main.
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const session = await Session.server(
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"sh",
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["-c", "printf '\\033[?1049h\\033[?1049lmain-again'; sleep 60"],
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{ rows: 24, cols: 80 },
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);
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await new Promise((r) => setTimeout(r, 300));
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const screen = await captureScreen(session.name, encodeAttach(24, 80));
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// Buffer is back to main — no position-0 alt-screen prefix.
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expect(screen.startsWith("\x1b[?1049h")).toBe(false);
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await session.close();
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}, 15000);
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// Note on PEEK: we do NOT test that PEEK omits ?1049h. xterm-addon-serialize
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// independently emits `\x1b[?1049h` at the start of its output when the
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// buffer is alternate, and that's pre-existing behavior outside this patch's
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// scope. This patch's contract is `getModePrefix(includeAltScreen)` — only
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// ATTACH passes `true`, so this patch adds nothing to PEEK either way.
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// Whether peek's client-side TERMINAL_SANITIZE round-trip loses alt-content
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// is a separate concern tracked outside #41.
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it("tracks ?1047 (legacy variant) as alt-screen too", async () => {
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const session = await Session.server(
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"sh",
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["-c", "printf '\\033[?1047h\\033[Halt-1047'; sleep 60"],
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{ rows: 24, cols: 80 },
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);
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await new Promise((r) => setTimeout(r, 300));
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const screen = await captureScreen(session.name, encodeAttach(24, 80));
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// Server normalizes to ?1049h on emit (the modern combined form) —
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// callers get consistent semantics regardless of which variant the
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// child used to enter.
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expect(screen.startsWith("\x1b[?1049h")).toBe(true);
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await session.close();
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}, 15000);
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});