Add first-class GitHub Copilot and Copilot ACP provider support across
model selection, runtime provider resolution, CLI sessions, delegated
subagents, cron jobs, and the Telegram gateway.
This also normalizes Copilot model catalogs and API modes, introduces a
Copilot ACP OpenAI-compatible shim, and fixes service-mode auth by
resolving Homebrew-installed gh binaries under launchd.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Two related bugs prevented users from reliably switching providers:
1. OPENAI_BASE_URL poisoning OpenRouter resolution: When a user with a
custom endpoint ran /model openrouter:model, _resolve_openrouter_runtime
picked up OPENAI_BASE_URL instead of the OpenRouter URL, causing model
validation to probe the wrong API and reject valid models.
Fix: skip OPENAI_BASE_URL when requested_provider is explicitly
'openrouter'.
2. Provider never saved to config: _save_model_choice() could save
config.model as a plain string. All five _model_flow_* functions then
checked isinstance(model, dict) before writing the provider — which
silently failed on strings. With no provider in config, auto-detection
would pick up stale credentials (e.g. Codex desktop app) instead of
the user's explicit choice.
Fix: _save_model_choice() now always saves as dict format. All flow
functions also normalize string->dict as a safety net before writing
provider.
Adds 4 regression tests. 2873 tests pass.
