Feat: Refactor error handling and enhance server capabilities

[aayank13]

• Introduced structured error handling with ErrorInfo and ErrorCode enums in mofa-kernel.
• Updated EngineError to provide machine-readable error codes and retryable status.
• Enhanced the server API by adding a new endpoint for resource refresh.
• Simplified error responses in the server by utilizing the new ErrorInfo structure.
• Improved model provider traits to include methods for loading and unloading models.
• Added backend health and feature reporting to enhance observability.
• Updated model status logic to derive from richer state information.
• Refactored model card structure to include execution state and availability.

[Copilot]

Pull request overview

This PR refactors the engine/kernel contracts to provide structured, machine-readable error handling and richer backend/model state, while expanding server and provider capabilities to support discovery/health reporting and manual refresh.

Changes:

• Introduces ErrorCode/ErrorInfo and updates EngineError to expose stable codes, retryability, and optional source provider.
• Expands model/runtime state (health, availability, residency, execution) and updates routing + status derivation accordingly.
• Enhances the HTTP API with /v1/discovery/refresh, richer status reporting, and standardized error responses.

Reviewed changes

Copilot reviewed 19 out of 20 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
mofa-kernel/src/types.rs	Adds backend/model state types, canonical model ID helpers, fallback policy, and richer request/response fields.
mofa-kernel/src/traits.rs	Extends provider trait with name/kind/features plus typed discover/health/load/unload.
mofa-kernel/src/lib.rs	Re-exports new error types (ErrorCode, ErrorInfo).
mofa-kernel/src/error.rs	Implements structured error info + stable error codes and retryability.
mofa-engine-sdk/src/server.rs	Standardizes error responses to ErrorInfo and adds /v1/discovery/refresh.
mofa-engine-sdk/src/lib.rs	Reorders module declarations (no functional change).
mofa-engine-core/src/router.rs	Refactors routing to use provider health/circuit state and richer model state; adds explainable decisions.
mofa-engine-core/src/memory.rs	Minor formatting-only refactor.
mofa-engine-core/src/lib.rs	Reorders module declarations/exports.
mofa-engine-core/src/engine.rs	Adds validated engine construction, refresh flow, health tracking, lifecycle loading, fallback policy, and richer events/status.
mofa-engine-core/src/config.rs	Adds checked config loading + validation; defaults host to 127.0.0.1.
mofa-engine-core/src/circuit_breaker.rs	Minor formatting-only refactor.
mofa-engine-core/src/backends/openai_compat.rs	Updates OpenAI-compatible backend to new Provider contract + lifecycle no-ops + capability checks.
mofa-engine-core/src/backends/ollama.rs	Updates Ollama backend to new Provider contract + discovery/health + load/unload hooks and residency inspection.
mofa-engine-core/src/backends.rs	New module file exporting provider backend implementations.
mofa-engine-app/src/main.rs	Switches production startup to checked config + Engine::try_new.
docs/openapi.yaml	Adds OpenAPI spec documenting refresh endpoint and structured errors.
docs/decisions/0001-stage-0-2-baseline.md	Adds ADR capturing baseline decisions (IDs, fallback, health/residency split, bind address).
docs/acceptance.md	Adds acceptance checklist tracking for stage 0–2 baseline.
.github/workflows/ci.yml	Adds Rust CI workflow (fmt/clippy/test).

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[Copilot]

Pull request overview

Copilot reviewed 19 out of 20 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 19 out of 20 changed files in this pull request and generated 3 comments.