fix: app_bot_login fails to initialize — GET /user not available to GitHub App installation tokens

[rnetser]

Problem

app_bot_login fails to initialize because the code uses get_user().login — an endpoint (GET /user) that is not available to GitHub App installation tokens. This is a GitHub platform limitation, not a permissions issue. Installation tokens authenticate as an app, not a user, so GET /user always returns 403.

Root Cause

webhook_server/libs/github_api.py line 555:

lambda: _github_app_api.get_user().login  # always 403 for app tokens

Impact

Feature	Normal behavior	When app_bot_login is empty
/cherry-pick-retry	Finds old failed cherry-pick PR → closes it → creates fresh retry	Skips close → duplicate cherry-pick PRs pile up
/rebase on bot PRs	Only assignee or maintainer can rebase	Any valid command runner can rebase (auth degradation)

Additionally, the error traceback is logged on every webhook event, spamming server logs.

Proposed Fix

Replace get_user().login with GET /app → {app.slug}[bot]:

app = _github_app_api.get_app()
self.app_bot_login = f"{app.slug}[bot]"

GET /app is designed for app tokens and returns the app metadata including slug.

Done

• Replace get_user().login with get_app().slug + [bot] suffix in github_api.py
• Update tests
• Verify no other code uses get_user() on app installation tokens