Adds a top-level `provider` slug to WorkspaceConfig and RuntimeConfig so
adapters can route to a specific gateway without re-implementing
slug-prefix parsing across hermes / claude-code / codex.
Resolution chain in load_config (mirrors how `model` resolves):
1. ``LLM_PROVIDER`` env var — what canvas Save+Restart sets so the
operator's Provider dropdown choice survives a CP-driven restart
(the regenerated /configs/config.yaml drops most user fields).
2. Explicit YAML ``provider:`` — operator pinned it in the file.
3. Derive from the model slug prefix for backward compat:
``anthropic:claude-opus-4-7`` → ``anthropic``
``minimax/abab7-chat-preview`` → ``minimax``
bare model names → ``""`` (let the adapter decide).
`runtime_config.provider` falls back to the top-level resolved
provider, the same shape PR #2438 added for `runtime_config.model`.
Why a separate field at all (we already parse the slug):
- Custom model aliases without a recognizable prefix need an
explicit signal — the canvas Provider dropdown writes it.
- Adapters were each rolling their own slug-parse (hermes's
derive-provider.sh, claude-code's adapter-default branch, etc.);
one resolution point in load_config kills that drift class.
- Canvas needs a stable storage field that doesn't get clobbered
every time the user picks a new model.
Backward-compatible: when `provider:` is absent, slug derivation
keeps every existing config.yaml working without a migration.
PR-1 of a multi-PR stack (Option B from RFC discussion). Subsequent
PRs plumb the field through workspace-server env, CP user-data,
adapters (hermes prefers explicit over derive-provider.sh), and
canvas Provider dropdown UI.
Tests cover all four resolution paths + runtime_config inheritance:
- test_provider_default_empty_when_bare_model
- test_provider_derived_from_colon_slug
- test_provider_derived_from_slash_slug
- test_provider_yaml_explicit_wins_over_derived
- test_provider_env_override_beats_yaml_and_derived
- test_runtime_config_provider_yaml_wins_over_top_level
- test_provider_default_from_default_model
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
067ad83ce5