app-server capReached reports true when output exactly equals outputBytesCap

[mturac]

I found a small edge case in app-server output cap handling.

When output length is exactly equal to outputBytesCap, capReached can be reported as true even though no output was actually truncated.

I tested three cases locally:

• below cap -> capReached = false
• exactly at cap -> capReached = false
• above cap -> capReached = true

The narrow fix is to derive capReached from whether the original chunk was actually shortened, rather than whether the observed byte count equals the cap.

I have a small local patch covering both command/exec and process/spawn if maintainers think this matches the intended protocol semantics.

Patch branch:
https://github.com/mturac/codex/tree/audit/cap-reached-exact-cap

Commit:
mturac@956b2a8