fix: bound stdin read so the process cannot outlive its render

[filipemb]

Problem

readStdin() iterates process.stdin until EOF. When the host writes the status JSON but keeps the write end open, that iteration never settles: the render finishes, but the process stays resident. On a long-lived host with a short refresh interval these accumulate — I found 77 of them alive, the oldest at 257 hours, holding ~2.3 GB.

Repro — spawn the CLI, write the payload, never call end():

const p = spawn(process.execPath, ['dist/ccstatusline.js'], { stdio: ['pipe', 'pipe', 'pipe'] });
p.stdin.write(JSON.stringify({ session_id: 't', model: { display_name: 'Opus' } })); // no end()
setTimeout(() => console.log('still alive'), 12000);

Before: still alive, indefinitely. After: exits in ~5s, having rendered the line.

Fix

Race the read against a timeout — 5000 ms default, CCSTATUSLINE_STDIN_TIMEOUT_MS to override. On timeout it resolves with whatever already arrived instead of discarding it: the payload is written in one shot, so a missing EOF means the EOF is missing, not the data, and the status line still renders correctly. finally clears the timer and pauses/unrefs the stream.

readStdin moves to src/utils/stdin.ts because the entrypoint runs main() on import, which makes the function untestable where it was.

Tests

src/utils/__tests__/stdin.test.ts covers three cases: TTY returns null, a normal close reads the payload, and no-EOF resolves with what arrived. The third one fails on main (times out) and passes with this change. The rest of the suite shows no new failures.