Two changes that complete the Copilot auth story (#7731 parts 3 and 4):
1. Switch OAuth client ID from opencode (Ov23li8tweQw6odWQebz) to VS Code
(Iv1.b507a08c87ecfe98). The old ID produces gho_* tokens that return
404 on /copilot_internal/v2/token, making token exchange non-functional.
The new ID produces ghu_* tokens that support exchange.
2. Derive enterprise API base URL from the proxy-ep field in the exchanged
token. Enterprise accounts get tokens containing e.g.
"proxy-ep=proxy.enterprise.githubcopilot.com" which is converted to
"https://api.enterprise.githubcopilot.com" and stored in the credential
pool. Individual accounts (no proxy-ep) continue using the default URL.
The COPILOT_API_BASE_URL env var remains as a user escape hatch.
Tested on both Individual and Enterprise Copilot accounts:
- Individual: device flow works, exchange succeeds, base_url=None (default)
- Enterprise: device flow works, exchange succeeds, 39 models returned
including claude-opus-4.6-1m (936K), enterprise base URL derived
Parts 3 and 4 of #7731.
Raw GitHub tokens (gho_/github_pat_/ghu_) are now exchanged for
short-lived Copilot API tokens via /copilot_internal/v2/token before
being used as Bearer credentials. This is required to access
internal-only models (e.g. claude-opus-4.6-1m with 1M context).
Implementation:
- exchange_copilot_token(): calls the token exchange endpoint with
in-process caching (dict keyed by SHA-256 fingerprint), refreshed
2 minutes before expiry. No disk persistence — gateway is long-running
so in-memory cache is sufficient.
- get_copilot_api_token(): convenience wrapper with graceful fallback —
returns exchanged token on success, raw token on failure.
- Both callers (hermes_cli/auth.py and agent/credential_pool.py) now
pipe the raw token through get_copilot_api_token() before use.
12 new tests covering exchange, caching, expiry, error handling,
fingerprinting, and caller integration. All 185 existing copilot/auth
tests pass.
Part 2 of #7731.
