docs(screenshots): document the 5s CDP ceiling and the full=True stall

[cryptoshrine]

Two distinct failure modes that both surface as the same unexplained TimeoutError, so they're easy to mistake for a dropped connection. Both are documented in interaction-skills/screenshots.md; no code changes.

1. Every CDP call has a hard five-second ceiling

_send() in helpers.py opens its socket with timeout=5.0, so any call needing longer than that fails. Not screenshot-specific:

call	result
js() blocked 3s	OK in 3.0s
js() blocked 7s	TimeoutError at exactly 5.0s
same 7s call, socket timeout raised to 30s	OK in 7.0s

The traceback ends in _ipc.py rather than naming the call that was made, which reads like a dead tab. It isn't — the daemon and tab are both fine, and the next call works.

2. full=True never returns when the window is hidden

full=True sets captureBeyondViewport, which needs a fresh composited frame for the whole scrollable area. A minimized or fully occluded window never produces one:

window state	capture	result
minimized	viewport	OK in 1.8s
minimized	full=True	still hanging past 2min, socket timeout raised to 90s
visible	full=True	OK in 0.4s

So it's a stall, not slowness — and it's invisible to anyone testing with the window on screen.

Measured on Windows 11 / Chrome 150 (Canary), harness at v0.1.8.

Note for maintainers

The 5s value is hard-coded and there's no way to raise it from a script without reaching past helpers._send into _ipc directly. If you'd take a patch making it configurable — an env var, or a per-call timeout= on cdp() — happy to follow up with one. I kept this PR docs-only since that's a behavioral change worth deciding separately.

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Summary by cubic

Documented two screenshot timeouts/stalls: a hard 5s ceiling on all CDP calls due to _send() socket timeout=5.0, and full=True never returning when the window is minimized or fully hidden.
Adds guidance to raise the window or use viewport captures, and clarifies the TimeoutError from _ipc.py isn’t a dropped connection.

^{Written for commit 147dd6a. Summary will update on new commits.}

[browser-harness-review]

✅ Skill review passed

Reviewed 1 file(s) — no findings.

[cubic-dev-ai]

No issues found across 1 file

_{Re-trigger cubic}