Configure Agent defaults with a workspace Provider model catalog

[SaladDay]

Agents now save a Harness, catalog model and environment/template default. Build → Models groups models under their Provider, with write-only Provider API keys; Agent forms select these models instead of requiring a model identifier. Provider headings are larger and clickable, while child model rows are smaller and read-only. Third-party credentials remain in Credentials.

Parsar owns workspace catalog data, permissions and product configuration. Core receives only the documented Harness selection and optional write-only Session execution input, using existing Codex, Claude Code and MiniMax Code execution paths. Opening chat starts no environment; the first message creates an independent Session. Its model, endpoint and key remain frozen through retries, Provider changes/deletion and restarts. Unsupported or unavailable configurations fail explicitly.

Validation:

• Full Linux make check, generated OpenAPI/sqlc checks, frontend typecheck/build and focused permission, encryption, snapshot, retry and protocol tests passed.
• Fresh independent blind review of the entire branch found no actionable in-scope defects; the reviewer independently passed focused Go tests.
• Integrated current main, ordered the Core migration after its Skills migration, and verified pinned official Python/Go client compatibility, including Sessions without the Harness extension.
• Browser checks covered Provider/model creation, Agent selection/save/read, and the requested Provider/model hierarchy and click behavior.
• Real MiniMax M3 execution passed for all three existing Harnesses, including file creation and conversation/file continuation after Core restart. Product-to-Core acceptance also passed: after Provider key rotation and deletion, the existing conversation continued and a new conversation failed explicitly.
• Standalone frontend lint still reports pre-existing findings in untouched code; no catalog files are affected. A direct macOS multi-package database run encountered shared-fixture interference; focused checks and the prescribed isolated Linux gate passed.

Evidence: Agent defaults acceptance, catalog acceptance, Harness contract, model execution contract.

Scope excludes new Harness implementations, legacy execution, Provider CRUD in Core, idle lifecycle changes and unrelated product redesign. The user authorized merging and updating the existing mx service after validation; deployment preserves its databases and existing Sessions.