test(config): add migration tests for litellm provider

* Implement tests for migrating configuration from v1 to v2 for the litellm provider.
* Validate the structure and values of the migrated configuration.
* Ensure migration rejects newer versions of the configuration.
fix(validate): enhance AI provider validation logic
* Consolidate provider validation into a dedicated method.
* Ensure at least one provider is specified and validate its type.
* Check for required fields based on provider type.
fix(mcpserver): update tool set to use new enrichment tool
* Replace RetryMetadataTool with RetryEnrichmentTool in the ToolSet.
fix(tools): refactor tools to use embedding and metadata runners
* Update tools to utilize EmbeddingRunner and MetadataRunner instead of Provider.
* Adjust method calls to align with the new runner interfaces.

internal/config/config.go

@@ -8,6 +8,7 @@ const (
 )
 
 type Config struct {
+	Version       int                 `yaml:"version"`
 	Server        ServerConfig        `yaml:"server"`
 	MCP           MCPConfig           `yaml:"mcp"`
 	Auth          AuthConfig          `yaml:"auth"`
@@ -37,11 +38,8 @@ type MCPConfig struct {
 	Version        string        `yaml:"version"`
 	Transport      string        `yaml:"transport"`
 	SessionTimeout time.Duration `yaml:"session_timeout"`
-	// PublicURL is the externally reachable base URL of this server (e.g. https://amcs.example.com).
-	// When set, it is used to build absolute icon URLs in the MCP server identity.
-	PublicURL string `yaml:"public_url"`
-	// Instructions is set at startup from the embedded memory.md and sent to MCP clients on initialise.
-	Instructions string `yaml:"-"`
+	PublicURL      string        `yaml:"public_url"`
+	Instructions   string        `yaml:"-"`
 }
 
 type AuthConfig struct {
@@ -77,52 +75,82 @@ type DatabaseConfig struct {
 	MaxConnIdleTime time.Duration `yaml:"max_conn_idle_time"`
 }
 
+// AIConfig (v2): named providers + per-role chains.
 type AIConfig struct {
-	Provider   string             `yaml:"provider"`
-	Embeddings AIEmbeddingConfig  `yaml:"embeddings"`
-	Metadata   AIMetadataConfig   `yaml:"metadata"`
-	LiteLLM    LiteLLMConfig      `yaml:"litellm"`
-	Ollama     OllamaConfig       `yaml:"ollama"`
-	OpenRouter OpenRouterAIConfig `yaml:"openrouter"`
+	Providers  map[string]ProviderConfig `yaml:"providers"`
+	Embeddings EmbeddingsRoleConfig      `yaml:"embeddings"`
+	Metadata   MetadataRoleConfig        `yaml:"metadata"`
+	Background *BackgroundRolesConfig    `yaml:"background,omitempty"`
 }
 
-type AIEmbeddingConfig struct {
-	Model      string `yaml:"model"`
-	Dimensions int    `yaml:"dimensions"`
+type ProviderConfig struct {
+	Type           string            `yaml:"type"`
+	BaseURL        string            `yaml:"base_url"`
+	APIKey         string            `yaml:"api_key"`
+	RequestHeaders map[string]string `yaml:"request_headers,omitempty"`
+	AppName        string            `yaml:"app_name,omitempty"`
+	SiteURL        string            `yaml:"site_url,omitempty"`
 }
 
-type AIMetadataConfig struct {
-	Model            string        `yaml:"model"`
-	FallbackModels   []string      `yaml:"fallback_models"`
-	FallbackModel    string        `yaml:"fallback_model"` // legacy single fallback
+type RoleTarget struct {
+	Provider string `yaml:"provider"`
+	Model    string `yaml:"model"`
+}
+
+type RoleChain struct {
+	Primary   RoleTarget   `yaml:"primary"`
+	Fallbacks []RoleTarget `yaml:"fallbacks,omitempty"`
+}
+
+type EmbeddingsRoleConfig struct {
+	Dimensions int          `yaml:"dimensions"`
+	Primary    RoleTarget   `yaml:"primary"`
+	Fallbacks  []RoleTarget `yaml:"fallbacks,omitempty"`
+}
+
+type MetadataRoleConfig struct {
 	Temperature      float64       `yaml:"temperature"`
 	LogConversations bool          `yaml:"log_conversations"`
 	Timeout          time.Duration `yaml:"timeout"`
+	Primary          RoleTarget    `yaml:"primary"`
+	Fallbacks        []RoleTarget  `yaml:"fallbacks,omitempty"`
 }
 
-type LiteLLMConfig struct {
-	BaseURL                string            `yaml:"base_url"`
-	APIKey                 string            `yaml:"api_key"`
-	UseResponsesAPI        bool              `yaml:"use_responses_api"`
-	RequestHeaders         map[string]string `yaml:"request_headers"`
-	EmbeddingModel         string            `yaml:"embedding_model"`
-	MetadataModel          string            `yaml:"metadata_model"`
-	FallbackMetadataModels []string          `yaml:"fallback_metadata_models"`
-	FallbackMetadataModel  string            `yaml:"fallback_metadata_model"` // legacy single fallback
+// BackgroundRolesConfig overrides the foreground chains for background workers
+// (backfill_embeddings, metadata_retry, reparse_metadata). Either field may be
+// nil to inherit the foreground role unchanged.
+type BackgroundRolesConfig struct {
+	Embeddings *RoleChain `yaml:"embeddings,omitempty"`
+	Metadata   *RoleChain `yaml:"metadata,omitempty"`
 }
 
-type OllamaConfig struct {
-	BaseURL        string            `yaml:"base_url"`
-	APIKey         string            `yaml:"api_key"`
-	RequestHeaders map[string]string `yaml:"request_headers"`
+// Chain returns primary followed by fallbacks (deduped, blanks dropped).
+func (e EmbeddingsRoleConfig) Chain() []RoleTarget {
+	return dedupeTargets(append([]RoleTarget{e.Primary}, e.Fallbacks...))
 }
 
-type OpenRouterAIConfig struct {
-	BaseURL      string            `yaml:"base_url"`
-	APIKey       string            `yaml:"api_key"`
-	AppName      string            `yaml:"app_name"`
-	SiteURL      string            `yaml:"site_url"`
-	ExtraHeaders map[string]string `yaml:"extra_headers"`
+func (m MetadataRoleConfig) Chain() []RoleTarget {
+	return dedupeTargets(append([]RoleTarget{m.Primary}, m.Fallbacks...))
+}
+
+func (c RoleChain) AsTargets() []RoleTarget {
+	return dedupeTargets(append([]RoleTarget{c.Primary}, c.Fallbacks...))
+}
+
+func dedupeTargets(in []RoleTarget) []RoleTarget {
+	out := make([]RoleTarget, 0, len(in))
+	seen := make(map[RoleTarget]struct{}, len(in))
+	for _, t := range in {
+		if t.Provider == "" || t.Model == "" {
+			continue
+		}
+		if _, ok := seen[t]; ok {
+			continue
+		}
+		seen[t] = struct{}{}
+		out = append(out, t)
+	}
+	return out
 }
 
 type CaptureConfig struct {
@@ -167,45 +195,3 @@ type MetadataRetryConfig struct {
 	MaxPerRun       int           `yaml:"max_per_run"`
 	IncludeArchived bool          `yaml:"include_archived"`
 }
-
-func (c AIMetadataConfig) EffectiveFallbackModels() []string {
-	models := make([]string, 0, len(c.FallbackModels)+1)
-	for _, model := range c.FallbackModels {
-		if model != "" {
-			models = append(models, model)
-		}
-	}
-	if c.FallbackModel != "" {
-		models = append(models, c.FallbackModel)
-	}
-	return dedupeNonEmpty(models)
-}
-
-func (c LiteLLMConfig) EffectiveFallbackMetadataModels() []string {
-	models := make([]string, 0, len(c.FallbackMetadataModels)+1)
-	for _, model := range c.FallbackMetadataModels {
-		if model != "" {
-			models = append(models, model)
-		}
-	}
-	if c.FallbackMetadataModel != "" {
-		models = append(models, c.FallbackMetadataModel)
-	}
-	return dedupeNonEmpty(models)
-}
-
-func dedupeNonEmpty(values []string) []string {
-	seen := make(map[string]struct{}, len(values))
-	out := make([]string, 0, len(values))
-	for _, value := range values {
-		if value == "" {
-			continue
-		}
-		if _, ok := seen[value]; ok {
-			continue
-		}
-		seen[value] = struct{}{}
-		out = append(out, value)
-	}
-	return out
-}