Agent doesn't/can't use GHPR tools to open a pull request

[ulugbekna]

I asked opus 4.5 to open pull requests but it doesn't use GHPR tools despite them being available.

repro:

1. tell agent to create a pull request with GHPR tools enabled
2. see how it doesn't quite know it can use GHPR tools to open a PR

Version: 1.109.0-insider (Universal)
Commit: a1728b98fa654220245c84bd92bb1baf13f730c6
Date: 2026-01-30T08:18:40.203Z
Electron: 39.3.0
ElectronBuildId: 13168319
Chromium: 142.0.7444.265
Node.js: 22.21.1
V8: 14.2.231.22-electron.0
OS: Darwin arm64 25.2.0

[alexr00]

We don't actually have a tool for this.