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.
2026-04-21 21:14:28 +02:00
parent 532d1560a3
commit 14e218d784
39 changed files with 2062 additions and 901 deletions
--- a/internal/config/config.go
+++ b/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
-}
--- a/internal/config/loader.go
+++ b/internal/config/loader.go
@@ -2,6 +2,7 @@ package config

 import (
 	"fmt"
+	"log/slog"
 	"os"
 	"strconv"
 	"strings"
@@ -12,6 +13,12 @@ import (
 )

 func Load(explicitPath string) (*Config, string, error) {
+	return LoadWithLogger(explicitPath, nil)
+}
+
+// LoadWithLogger is Load with a logger surface for migration notices. Passing
+// nil is fine — migration events will simply not be logged.
+func LoadWithLogger(explicitPath string, log *slog.Logger) (*Config, string, error) {
 	path := ResolvePath(explicitPath)

 	data, err := os.ReadFile(path)
@@ -19,10 +26,40 @@ func Load(explicitPath string) (*Config, string, error) {
 		return nil, path, fmt.Errorf("read config %q: %w", path, err)
 	}

-	cfg := defaultConfig()
-	if err := yaml.Unmarshal(data, &cfg); err != nil {
+	raw := map[string]any{}
+	if err := yaml.Unmarshal(data, &raw); err != nil {
 		return nil, path, fmt.Errorf("decode config %q: %w", path, err)
 	}
+	if raw == nil {
+		raw = map[string]any{}
+	}
+
+	applied, err := Migrate(raw)
+	if err != nil {
+		return nil, path, fmt.Errorf("migrate config %q: %w", path, err)
+	}
+
+	if len(applied) > 0 {
+		if err := rewriteConfigFile(path, data, raw); err != nil {
+			return nil, path, err
+		}
+		if log != nil {
+			for _, step := range applied {
+				log.Warn("config migrated",
+					slog.String("path", path),
+					slog.Int("from_version", step.From),
+					slog.Int("to_version", step.To),
+					slog.String("describe", step.Describe),
+				)
+			}
+		}
+	}
+
+	cfg, err := decodeTyped(raw)
+	if err != nil {
+		return nil, path, fmt.Errorf("decode migrated config %q: %w", path, err)
+	}
+	cfg.Version = CurrentConfigVersion

 	applyEnvOverrides(&cfg)
 	if err := cfg.Validate(); err != nil {
@@ -32,6 +69,34 @@ func Load(explicitPath string) (*Config, string, error) {
 	return &cfg, path, nil
 }

+func decodeTyped(raw map[string]any) (Config, error) {
+	out, err := yaml.Marshal(raw)
+	if err != nil {
+		return Config{}, fmt.Errorf("re-marshal migrated config: %w", err)
+	}
+	cfg := defaultConfig()
+	if err := yaml.Unmarshal(out, &cfg); err != nil {
+		return Config{}, err
+	}
+	return cfg, nil
+}
+
+func rewriteConfigFile(path string, original []byte, migrated map[string]any) error {
+	backupPath := fmt.Sprintf("%s.bak.%d", path, time.Now().Unix())
+	if err := os.WriteFile(backupPath, original, 0o600); err != nil {
+		return fmt.Errorf("write backup %q: %w", backupPath, err)
+	}
+
+	out, err := yaml.Marshal(migrated)
+	if err != nil {
+		return fmt.Errorf("marshal migrated config: %w", err)
+	}
+	if err := os.WriteFile(path, out, 0o600); err != nil {
+		return fmt.Errorf("write migrated config %q: %w", path, err)
+	}
+	return nil
+}
+
 func ResolvePath(explicitPath string) string {
 	if path := strings.TrimSpace(explicitPath); path != "" {
 		if path != ".yaml" && path != ".yml" {
@@ -49,6 +114,7 @@ func ResolvePath(explicitPath string) string {
 func defaultConfig() Config {
 	info := buildinfo.Current()
 	return Config{
+		Version: CurrentConfigVersion,
 		Server: ServerConfig{
 			Host:         "0.0.0.0",
 			Port:         8080,
@@ -69,20 +135,14 @@ func defaultConfig() Config {
 			QueryParam: "key",
 		},
 		AI: AIConfig{
-			Provider: "litellm",
-			Embeddings: AIEmbeddingConfig{
-				Model:      "openai/text-embedding-3-small",
+			Providers: map[string]ProviderConfig{},
+			Embeddings: EmbeddingsRoleConfig{
 				Dimensions: 1536,
 			},
-			Metadata: AIMetadataConfig{
-				Model:       "gpt-4o-mini",
+			Metadata: MetadataRoleConfig{
 				Temperature: 0.1,
 				Timeout:     10 * time.Second,
 			},
-			Ollama: OllamaConfig{
-				BaseURL: "http://localhost:11434/v1",
-				APIKey:  "ollama",
-			},
 		},
 		Capture: CaptureConfig{
 			Source: DefaultSource,
@@ -119,11 +179,12 @@ func defaultConfig() Config {
 func applyEnvOverrides(cfg *Config) {
 	overrideString(&cfg.Database.URL, "AMCS_DATABASE_URL")
 	overrideString(&cfg.MCP.PublicURL, "AMCS_PUBLIC_URL")
-	overrideString(&cfg.AI.LiteLLM.BaseURL, "AMCS_LITELLM_BASE_URL")
-	overrideString(&cfg.AI.LiteLLM.APIKey, "AMCS_LITELLM_API_KEY")
-	overrideString(&cfg.AI.Ollama.BaseURL, "AMCS_OLLAMA_BASE_URL")
-	overrideString(&cfg.AI.Ollama.APIKey, "AMCS_OLLAMA_API_KEY")
-	overrideString(&cfg.AI.OpenRouter.APIKey, "AMCS_OPENROUTER_API_KEY")
+
+	overrideProviderField(cfg, "AMCS_LITELLM_BASE_URL", "litellm", func(p *ProviderConfig, v string) { p.BaseURL = v })
+	overrideProviderField(cfg, "AMCS_LITELLM_API_KEY", "litellm", func(p *ProviderConfig, v string) { p.APIKey = v })
+	overrideProviderField(cfg, "AMCS_OLLAMA_BASE_URL", "ollama", func(p *ProviderConfig, v string) { p.BaseURL = v })
+	overrideProviderField(cfg, "AMCS_OLLAMA_API_KEY", "ollama", func(p *ProviderConfig, v string) { p.APIKey = v })
+	overrideProviderField(cfg, "AMCS_OPENROUTER_API_KEY", "openrouter", func(p *ProviderConfig, v string) { p.APIKey = v })

 	if value, ok := os.LookupEnv("AMCS_SERVER_PORT"); ok {
 		if port, err := strconv.Atoi(strings.TrimSpace(value)); err == nil {
@@ -132,6 +193,24 @@ func applyEnvOverrides(cfg *Config) {
 	}
 }

+// overrideProviderField applies an env var to every configured provider of the
+// given type. This preserves the v1 behaviour where e.g. AMCS_LITELLM_API_KEY
+// rewrote the single litellm block — in v2 it rewrites every litellm provider.
+func overrideProviderField(cfg *Config, envKey, providerType string, apply func(*ProviderConfig, string)) {
+	value, ok := os.LookupEnv(envKey)
+	if !ok {
+		return
+	}
+	value = strings.TrimSpace(value)
+	for name, p := range cfg.AI.Providers {
+		if p.Type != providerType {
+			continue
+		}
+		apply(&p, value)
+		cfg.AI.Providers[name] = p
+	}
+}
+
 func overrideString(target *string, envKey string) {
 	if value, ok := os.LookupEnv(envKey); ok {
 		*target = strings.TrimSpace(value)
--- a/internal/config/loader_test.go
+++ b/internal/config/loader_test.go
@@ -31,9 +31,8 @@ func TestResolvePathIgnoresBareYAMLExtension(t *testing.T) {
 	}
 }

-func TestLoadAppliesEnvOverrides(t *testing.T) {
-	configPath := filepath.Join(t.TempDir(), "test.yaml")
-	if err := os.WriteFile(configPath, []byte(`
+const v2ConfigYAML = `
+version: 2
 server:
  port: 8080
 mcp:
@@ -46,18 +45,30 @@ auth:
 database:
  url: "postgres://from-file"
 ai:
-  provider: "litellm"
+  providers:
+    default:
+      type: "litellm"
+      base_url: "http://localhost:4000/v1"
+      api_key: "file-key"
  embeddings:
    dimensions: 1536
-  litellm:
-    base_url: "http://localhost:4000/v1"
-    api_key: "file-key"
+    primary:
+      provider: "default"
+      model: "text-embed"
+  metadata:
+    primary:
+      provider: "default"
+      model: "gpt-4"
 search:
  default_limit: 10
  max_limit: 50
 logging:
  level: "info"
-`), 0o600); err != nil {
+`
+
+func TestLoadAppliesEnvOverrides(t *testing.T) {
+	configPath := filepath.Join(t.TempDir(), "test.yaml")
+	if err := os.WriteFile(configPath, []byte(v2ConfigYAML), 0o600); err != nil {
 		t.Fatalf("write config: %v", err)
 	}

@@ -76,8 +87,8 @@ logging:
 	if cfg.Database.URL != "postgres://from-env" {
 		t.Fatalf("database url = %q, want env override", cfg.Database.URL)
 	}
-	if cfg.AI.LiteLLM.APIKey != "env-key" {
-		t.Fatalf("litellm api key = %q, want env override", cfg.AI.LiteLLM.APIKey)
+	if cfg.AI.Providers["default"].APIKey != "env-key" {
+		t.Fatalf("litellm api key = %q, want env override", cfg.AI.Providers["default"].APIKey)
 	}
 	if cfg.Server.Port != 9090 {
 		t.Fatalf("server port = %d, want 9090", cfg.Server.Port)
@@ -90,10 +101,12 @@ logging:
 func TestLoadAppliesOllamaEnvOverrides(t *testing.T) {
 	configPath := filepath.Join(t.TempDir(), "test.yaml")
 	if err := os.WriteFile(configPath, []byte(`
+version: 2
 server:
  port: 8080
 mcp:
  path: "/mcp"
+  session_timeout: "10m"
 auth:
  keys:
    - id: "test"
@@ -101,15 +114,20 @@ auth:
 database:
  url: "postgres://from-file"
 ai:
-  provider: "ollama"
+  providers:
+    local:
+      type: "ollama"
+      base_url: "http://localhost:11434/v1"
+      api_key: "ollama"
  embeddings:
-    model: "nomic-embed-text"
    dimensions: 768
+    primary:
+      provider: "local"
+      model: "nomic-embed-text"
  metadata:
-    model: "llama3.2"
-  ollama:
-    base_url: "http://localhost:11434/v1"
-    api_key: "ollama"
+    primary:
+      provider: "local"
+      model: "llama3.2"
 search:
  default_limit: 10
  max_limit: 50
@@ -127,10 +145,77 @@ logging:
 		t.Fatalf("Load() error = %v", err)
 	}

-	if cfg.AI.Ollama.BaseURL != "https://ollama.example.com/v1" {
-		t.Fatalf("ollama base url = %q, want env override", cfg.AI.Ollama.BaseURL)
+	p := cfg.AI.Providers["local"]
+	if p.BaseURL != "https://ollama.example.com/v1" {
+		t.Fatalf("ollama base url = %q, want env override", p.BaseURL)
 	}
-	if cfg.AI.Ollama.APIKey != "remote-key" {
-		t.Fatalf("ollama api key = %q, want env override", cfg.AI.Ollama.APIKey)
+	if p.APIKey != "remote-key" {
+		t.Fatalf("ollama api key = %q, want env override", p.APIKey)
+	}
+}
+
+func TestLoadMigratesV1Config(t *testing.T) {
+	configPath := filepath.Join(t.TempDir(), "v1.yaml")
+	v1 := `
+server:
+  port: 8080
+mcp:
+  path: "/mcp"
+  session_timeout: "10m"
+auth:
+  keys:
+    - id: "test"
+      value: "secret"
+database:
+  url: "postgres://from-file"
+ai:
+  provider: "litellm"
+  embeddings:
+    model: "text-embed"
+    dimensions: 1536
+  metadata:
+    model: "gpt-4"
+    temperature: 0.2
+    fallback_models: ["gpt-3.5"]
+  litellm:
+    base_url: "http://localhost:4000/v1"
+    api_key: "file-key"
+search:
+  default_limit: 10
+  max_limit: 50
+logging:
+  level: "info"
+`
+	if err := os.WriteFile(configPath, []byte(v1), 0o600); err != nil {
+		t.Fatalf("write config: %v", err)
+	}
+
+	cfg, _, err := Load(configPath)
+	if err != nil {
+		t.Fatalf("Load() error = %v", err)
+	}
+
+	if cfg.Version != CurrentConfigVersion {
+		t.Fatalf("version = %d, want %d", cfg.Version, CurrentConfigVersion)
+	}
+	if p, ok := cfg.AI.Providers["default"]; !ok || p.Type != "litellm" || p.APIKey != "file-key" {
+		t.Fatalf("providers[default] = %+v, want litellm/file-key", p)
+	}
+	if cfg.AI.Embeddings.Primary.Model != "text-embed" || cfg.AI.Embeddings.Primary.Provider != "default" {
+		t.Fatalf("embeddings.primary = %+v, want default/text-embed", cfg.AI.Embeddings.Primary)
+	}
+	if cfg.AI.Metadata.Primary.Model != "gpt-4" || cfg.AI.Metadata.Primary.Provider != "default" {
+		t.Fatalf("metadata.primary = %+v, want default/gpt-4", cfg.AI.Metadata.Primary)
+	}
+	if len(cfg.AI.Metadata.Fallbacks) != 1 || cfg.AI.Metadata.Fallbacks[0].Model != "gpt-3.5" {
+		t.Fatalf("metadata.fallbacks = %+v, want [default/gpt-3.5]", cfg.AI.Metadata.Fallbacks)
+	}
+
+	entries, err := filepath.Glob(configPath + ".bak.*")
+	if err != nil {
+		t.Fatalf("glob backups: %v", err)
+	}
+	if len(entries) != 1 {
+		t.Fatalf("backup files = %d, want 1", len(entries))
 	}
 }
--- a/internal/config/migrate.go
+++ b/internal/config/migrate.go
@@ -0,0 +1,341 @@
+package config
+
+import (
+	"fmt"
+	"sort"
+)
+
+// CurrentConfigVersion is the schema version this binary expects. Files at a
+// lower version are migrated automatically when loaded.
+const CurrentConfigVersion = 2
+
+// ConfigMigration upgrades a raw YAML map by one version.
+type ConfigMigration struct {
+	From, To int
+	Describe string
+	Apply    func(map[string]any) error
+}
+
+// migrations is the ordered ladder of upgrades. Add new entries at the end.
+var migrations = []ConfigMigration{
+	{From: 1, To: 2, Describe: "named providers + role chains", Apply: migrateV1toV2},
+}
+
+// Migrate brings raw up to CurrentConfigVersion in place. Returns the list of
+// migrations that were applied (may be empty if already current).
+func Migrate(raw map[string]any) ([]ConfigMigration, error) {
+	if raw == nil {
+		return nil, fmt.Errorf("migrate: raw config is nil")
+	}
+
+	version := readVersion(raw)
+	if version > CurrentConfigVersion {
+		return nil, fmt.Errorf("migrate: config version %d is newer than supported version %d", version, CurrentConfigVersion)
+	}
+
+	applied := make([]ConfigMigration, 0)
+	for {
+		if version >= CurrentConfigVersion {
+			break
+		}
+		step, ok := findMigration(version)
+		if !ok {
+			return nil, fmt.Errorf("migrate: no migration registered from version %d", version)
+		}
+		if err := step.Apply(raw); err != nil {
+			return nil, fmt.Errorf("migrate v%d->v%d: %w", step.From, step.To, err)
+		}
+		raw["version"] = step.To
+		version = step.To
+		applied = append(applied, step)
+	}
+	return applied, nil
+}
+
+func findMigration(from int) (ConfigMigration, bool) {
+	for _, m := range migrations {
+		if m.From == from {
+			return m, true
+		}
+	}
+	return ConfigMigration{}, false
+}
+
+// readVersion returns the version from raw. Files without a version field are
+// treated as version 1 (the original schema).
+func readVersion(raw map[string]any) int {
+	v, ok := raw["version"]
+	if !ok {
+		return 1
+	}
+	switch n := v.(type) {
+	case int:
+		return n
+	case int64:
+		return int(n)
+	case float64:
+		return int(n)
+	}
+	return 1
+}
+
+// migrateV1toV2 lifts the single-provider config into the named-providers +
+// role-chains layout. The pre-v2 config implicitly used one provider for both
+// embeddings and metadata; we materialise that as a provider named "default".
+func migrateV1toV2(raw map[string]any) error {
+	aiRaw := mapValue(raw, "ai")
+	if aiRaw == nil {
+		aiRaw = map[string]any{}
+	}
+
+	providerType := stringValue(aiRaw, "provider")
+	if providerType == "" {
+		providerType = "litellm"
+	}
+
+	providers, embeddingModel, metadataModel, fallbackModels := buildV1Provider(aiRaw, providerType)
+
+	embeddingsOld := mapValue(aiRaw, "embeddings")
+	dimensions := intValue(embeddingsOld, "dimensions")
+	if dimensions <= 0 {
+		dimensions = 1536
+	}
+	if embeddingModel == "" {
+		embeddingModel = stringValue(embeddingsOld, "model")
+	}
+
+	metadataOld := mapValue(aiRaw, "metadata")
+	if metadataModel == "" {
+		metadataModel = stringValue(metadataOld, "model")
+	}
+	temperature := floatValue(metadataOld, "temperature")
+	logConversations := boolValue(metadataOld, "log_conversations")
+	timeoutStr := stringValue(metadataOld, "timeout")
+
+	if list := stringListValue(metadataOld, "fallback_models"); len(list) > 0 {
+		fallbackModels = append(fallbackModels, list...)
+	}
+	if v := stringValue(metadataOld, "fallback_model"); v != "" {
+		fallbackModels = append(fallbackModels, v)
+	}
+
+	embeddings := map[string]any{
+		"dimensions": dimensions,
+		"primary":    map[string]any{"provider": "default", "model": embeddingModel},
+	}
+
+	metadata := map[string]any{
+		"temperature":       temperature,
+		"log_conversations": logConversations,
+		"primary":           map[string]any{"provider": "default", "model": metadataModel},
+	}
+	if timeoutStr != "" {
+		metadata["timeout"] = timeoutStr
+	}
+	if fallbacks := chainTargets("default", fallbackModels); len(fallbacks) > 0 {
+		metadata["fallbacks"] = fallbacks
+	}
+
+	raw["ai"] = map[string]any{
+		"providers":  providers,
+		"embeddings": embeddings,
+		"metadata":   metadata,
+	}
+	return nil
+}
+
+func buildV1Provider(aiRaw map[string]any, providerType string) (map[string]any, string, string, []string) {
+	providers := map[string]any{}
+	defaultEntry := map[string]any{"type": providerType}
+	embedModel := ""
+	metaModel := ""
+	var fallbacks []string
+
+	switch providerType {
+	case "litellm":
+		block := mapValue(aiRaw, "litellm")
+		copyKeys(defaultEntry, block, "base_url", "api_key")
+		copyHeaders(defaultEntry, block, "request_headers")
+		embedModel = stringValue(block, "embedding_model")
+		metaModel = stringValue(block, "metadata_model")
+		if list := stringListValue(block, "fallback_metadata_models"); len(list) > 0 {
+			fallbacks = append(fallbacks, list...)
+		}
+		if v := stringValue(block, "fallback_metadata_model"); v != "" {
+			fallbacks = append(fallbacks, v)
+		}
+	case "ollama":
+		block := mapValue(aiRaw, "ollama")
+		copyKeys(defaultEntry, block, "base_url", "api_key")
+		copyHeaders(defaultEntry, block, "request_headers")
+	case "openrouter":
+		block := mapValue(aiRaw, "openrouter")
+		copyKeys(defaultEntry, block, "base_url", "api_key", "app_name", "site_url")
+		copyHeaders(defaultEntry, block, "extra_headers")
+		// rename: extra_headers → request_headers
+		if hdr, ok := defaultEntry["extra_headers"]; ok {
+			defaultEntry["request_headers"] = hdr
+			delete(defaultEntry, "extra_headers")
+		}
+	}
+
+	providers["default"] = defaultEntry
+	return providers, embedModel, metaModel, fallbacks
+}
+
+func chainTargets(provider string, models []string) []any {
+	out := make([]any, 0, len(models))
+	seen := map[string]struct{}{}
+	for _, m := range models {
+		if m == "" {
+			continue
+		}
+		key := provider + "|" + m
+		if _, ok := seen[key]; ok {
+			continue
+		}
+		seen[key] = struct{}{}
+		out = append(out, map[string]any{"provider": provider, "model": m})
+	}
+	return out
+}
+
+func mapValue(raw map[string]any, key string) map[string]any {
+	if raw == nil {
+		return nil
+	}
+	v, ok := raw[key]
+	if !ok {
+		return nil
+	}
+	switch m := v.(type) {
+	case map[string]any:
+		return m
+	case map[any]any:
+		return convertAnyMap(m)
+	}
+	return nil
+}
+
+func convertAnyMap(in map[any]any) map[string]any {
+	out := make(map[string]any, len(in))
+	keys := make([]string, 0, len(in))
+	for k, v := range in {
+		ks, ok := k.(string)
+		if !ok {
+			continue
+		}
+		keys = append(keys, ks)
+		out[ks] = v
+	}
+	sort.Strings(keys)
+	return out
+}
+
+func stringValue(raw map[string]any, key string) string {
+	if raw == nil {
+		return ""
+	}
+	v, ok := raw[key]
+	if !ok {
+		return ""
+	}
+	if s, ok := v.(string); ok {
+		return s
+	}
+	return ""
+}
+
+func intValue(raw map[string]any, key string) int {
+	if raw == nil {
+		return 0
+	}
+	switch n := raw[key].(type) {
+	case int:
+		return n
+	case int64:
+		return int(n)
+	case float64:
+		return int(n)
+	}
+	return 0
+}
+
+func floatValue(raw map[string]any, key string) float64 {
+	if raw == nil {
+		return 0
+	}
+	switch n := raw[key].(type) {
+	case float64:
+		return n
+	case int:
+		return float64(n)
+	case int64:
+		return float64(n)
+	}
+	return 0
+}
+
+func boolValue(raw map[string]any, key string) bool {
+	if raw == nil {
+		return false
+	}
+	if b, ok := raw[key].(bool); ok {
+		return b
+	}
+	return false
+}
+
+func stringListValue(raw map[string]any, key string) []string {
+	if raw == nil {
+		return nil
+	}
+	v, ok := raw[key]
+	if !ok {
+		return nil
+	}
+	list, ok := v.([]any)
+	if !ok {
+		return nil
+	}
+	out := make([]string, 0, len(list))
+	for _, item := range list {
+		if s, ok := item.(string); ok && s != "" {
+			out = append(out, s)
+		}
+	}
+	return out
+}
+
+func copyKeys(dst, src map[string]any, keys ...string) {
+	if src == nil {
+		return
+	}
+	for _, k := range keys {
+		if v, ok := src[k]; ok {
+			dst[k] = v
+		}
+	}
+}
+
+func copyHeaders(dst, src map[string]any, key string) {
+	if src == nil {
+		return
+	}
+	v, ok := src[key]
+	if !ok {
+		return
+	}
+	switch headers := v.(type) {
+	case map[string]any:
+		if len(headers) == 0 {
+			return
+		}
+		dst[key] = headers
+	case map[any]any:
+		if len(headers) == 0 {
+			return
+		}
+		dst[key] = convertAnyMap(headers)
+	}
+}
--- a/internal/config/migrate_test.go
+++ b/internal/config/migrate_test.go
@@ -0,0 +1,77 @@
+package config
+
+import "testing"
+
+func TestMigrateV1ToV2Litellm(t *testing.T) {
+	raw := map[string]any{
+		"ai": map[string]any{
+			"provider": "litellm",
+			"embeddings": map[string]any{
+				"model":      "text-embedding-3-small",
+				"dimensions": 1536,
+			},
+			"metadata": map[string]any{
+				"model":           "gpt-4o-mini",
+				"temperature":     0.2,
+				"fallback_models": []any{"gpt-4.1-mini"},
+			},
+			"litellm": map[string]any{
+				"base_url": "http://localhost:4000/v1",
+				"api_key":  "secret",
+			},
+		},
+	}
+
+	applied, err := Migrate(raw)
+	if err != nil {
+		t.Fatalf("Migrate() error = %v", err)
+	}
+	if len(applied) != 1 || applied[0].From != 1 || applied[0].To != 2 {
+		t.Fatalf("applied = %+v, want [v1->v2]", applied)
+	}
+	if got := readVersion(raw); got != CurrentConfigVersion {
+		t.Fatalf("version = %d, want %d", got, CurrentConfigVersion)
+	}
+
+	ai := mapValue(raw, "ai")
+	providers := mapValue(ai, "providers")
+	def := mapValue(providers, "default")
+	if got := stringValue(def, "type"); got != "litellm" {
+		t.Fatalf("providers.default.type = %q, want litellm", got)
+	}
+	if got := stringValue(def, "base_url"); got != "http://localhost:4000/v1" {
+		t.Fatalf("providers.default.base_url = %q", got)
+	}
+
+	emb := mapValue(ai, "embeddings")
+	embPrimary := mapValue(emb, "primary")
+	if stringValue(embPrimary, "provider") != "default" || stringValue(embPrimary, "model") != "text-embedding-3-small" {
+		t.Fatalf("embeddings.primary = %+v, want default/text-embedding-3-small", embPrimary)
+	}
+
+	meta := mapValue(ai, "metadata")
+	metaPrimary := mapValue(meta, "primary")
+	if stringValue(metaPrimary, "provider") != "default" || stringValue(metaPrimary, "model") != "gpt-4o-mini" {
+		t.Fatalf("metadata.primary = %+v, want default/gpt-4o-mini", metaPrimary)
+	}
+	fallbacks, ok := meta["fallbacks"].([]any)
+	if !ok || len(fallbacks) != 1 {
+		t.Fatalf("metadata.fallbacks = %#v, want len=1", meta["fallbacks"])
+	}
+	firstFallback, ok := fallbacks[0].(map[string]any)
+	if !ok {
+		t.Fatalf("metadata.fallbacks[0] type = %T, want map[string]any", fallbacks[0])
+	}
+	if stringValue(firstFallback, "provider") != "default" || stringValue(firstFallback, "model") != "gpt-4.1-mini" {
+		t.Fatalf("metadata fallback = %+v, want default/gpt-4.1-mini", firstFallback)
+	}
+}
+
+func TestMigrateRejectsNewerVersion(t *testing.T) {
+	raw := map[string]any{"version": CurrentConfigVersion + 1}
+
+	_, err := Migrate(raw)
+	if err == nil {
+		t.Fatal("Migrate() error = nil, want error for newer config version")
+	}
+}
--- a/internal/config/validate.go
+++ b/internal/config/validate.go
@@ -45,38 +45,8 @@ func (c Config) Validate() error {
 		return fmt.Errorf("invalid config: mcp.session_timeout must be greater than zero")
 	}

-	switch c.AI.Provider {
-	case "litellm", "ollama", "openrouter":
-	default:
-		return fmt.Errorf("invalid config: unsupported ai.provider %q", c.AI.Provider)
-	}
-
-	if c.AI.Embeddings.Dimensions <= 0 {
-		return fmt.Errorf("invalid config: ai.embeddings.dimensions must be greater than zero")
-	}
-
-	switch c.AI.Provider {
-	case "litellm":
-		if strings.TrimSpace(c.AI.LiteLLM.BaseURL) == "" {
-			return fmt.Errorf("invalid config: ai.litellm.base_url is required when ai.provider=litellm")
-		}
-		if strings.TrimSpace(c.AI.LiteLLM.APIKey) == "" {
-			return fmt.Errorf("invalid config: ai.litellm.api_key is required when ai.provider=litellm")
-		}
-	case "ollama":
-		if strings.TrimSpace(c.AI.Ollama.BaseURL) == "" {
-			return fmt.Errorf("invalid config: ai.ollama.base_url is required when ai.provider=ollama")
-		}
-		if strings.TrimSpace(c.AI.Ollama.APIKey) == "" {
-			return fmt.Errorf("invalid config: ai.ollama.api_key is required when ai.provider=ollama")
-		}
-	case "openrouter":
-		if strings.TrimSpace(c.AI.OpenRouter.BaseURL) == "" {
-			return fmt.Errorf("invalid config: ai.openrouter.base_url is required when ai.provider=openrouter")
-		}
-		if strings.TrimSpace(c.AI.OpenRouter.APIKey) == "" {
-			return fmt.Errorf("invalid config: ai.openrouter.api_key is required when ai.provider=openrouter")
-		}
+	if err := c.AI.validate(); err != nil {
+		return err
 	}

 	if c.Server.Port <= 0 {
@@ -108,3 +78,61 @@ func (c Config) Validate() error {

 	return nil
 }
+
+func (a AIConfig) validate() error {
+	if len(a.Providers) == 0 {
+		return fmt.Errorf("invalid config: ai.providers must contain at least one entry")
+	}
+	for name, p := range a.Providers {
+		if strings.TrimSpace(name) == "" {
+			return fmt.Errorf("invalid config: ai.providers contains an entry with an empty name")
+		}
+		switch p.Type {
+		case "litellm", "ollama", "openrouter":
+		default:
+			return fmt.Errorf("invalid config: ai.providers.%s.type %q is not supported", name, p.Type)
+		}
+		if strings.TrimSpace(p.BaseURL) == "" {
+			return fmt.Errorf("invalid config: ai.providers.%s.base_url is required", name)
+		}
+		if strings.TrimSpace(p.APIKey) == "" {
+			return fmt.Errorf("invalid config: ai.providers.%s.api_key is required", name)
+		}
+	}
+
+	if a.Embeddings.Dimensions <= 0 {
+		return fmt.Errorf("invalid config: ai.embeddings.dimensions must be greater than zero")
+	}
+
+	if err := a.validateChain("ai.embeddings", a.Embeddings.Chain()); err != nil {
+		return err
+	}
+	if err := a.validateChain("ai.metadata", a.Metadata.Chain()); err != nil {
+		return err
+	}
+	if a.Background != nil {
+		if a.Background.Embeddings != nil {
+			if err := a.validateChain("ai.background.embeddings", a.Background.Embeddings.AsTargets()); err != nil {
+				return err
+			}
+		}
+		if a.Background.Metadata != nil {
+			if err := a.validateChain("ai.background.metadata", a.Background.Metadata.AsTargets()); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}
+
+func (a AIConfig) validateChain(prefix string, chain []RoleTarget) error {
+	if len(chain) == 0 {
+		return fmt.Errorf("invalid config: %s.primary must reference a configured provider and model", prefix)
+	}
+	for i, target := range chain {
+		if _, ok := a.Providers[target.Provider]; !ok {
+			return fmt.Errorf("invalid config: %s[%d] references unknown provider %q", prefix, i, target.Provider)
+		}
+	}
+	return nil
+}
--- a/internal/config/validate_test.go
+++ b/internal/config/validate_test.go
@@ -7,28 +7,23 @@ import (

 func validConfig() Config {
 	return Config{
-		Server: ServerConfig{Port: 8080},
-		MCP:    MCPConfig{Path: "/mcp", SessionTimeout: 10 * time.Minute},
+		Version: CurrentConfigVersion,
+		Server:  ServerConfig{Port: 8080},
+		MCP:     MCPConfig{Path: "/mcp", SessionTimeout: 10 * time.Minute},
 		Auth: AuthConfig{
 			Keys: []APIKey{{ID: "test", Value: "secret"}},
 		},
 		Database: DatabaseConfig{URL: "postgres://example"},
 		AI: AIConfig{
-			Provider: "litellm",
-			Embeddings: AIEmbeddingConfig{
+			Providers: map[string]ProviderConfig{
+				"default": {Type: "litellm", BaseURL: "http://localhost:4000/v1", APIKey: "key"},
+			},
+			Embeddings: EmbeddingsRoleConfig{
 				Dimensions: 1536,
+				Primary:    RoleTarget{Provider: "default", Model: "text-embed"},
 			},
-			LiteLLM: LiteLLMConfig{
-				BaseURL: "http://localhost:4000/v1",
-				APIKey:  "key",
-			},
-			Ollama: OllamaConfig{
-				BaseURL: "http://localhost:11434/v1",
-				APIKey:  "ollama",
-			},
-			OpenRouter: OpenRouterAIConfig{
-				BaseURL: "https://openrouter.ai/api/v1",
-				APIKey:  "key",
+			Metadata: MetadataRoleConfig{
+				Primary: RoleTarget{Provider: "default", Model: "gpt-4"},
 			},
 		},
 		Search:  SearchConfig{DefaultLimit: 10, MaxLimit: 50},
@@ -36,29 +31,44 @@ func validConfig() Config {
 	}
 }

-func TestValidateAcceptsSupportedProviders(t *testing.T) {
-	cfg := validConfig()
-	if err := cfg.Validate(); err != nil {
-		t.Fatalf("Validate litellm error = %v", err)
-	}
-
-	cfg.AI.Provider = "ollama"
-	if err := cfg.Validate(); err != nil {
-		t.Fatalf("Validate ollama error = %v", err)
-	}
-
-	cfg.AI.Provider = "openrouter"
-	if err := cfg.Validate(); err != nil {
-		t.Fatalf("Validate openrouter error = %v", err)
+func TestValidateAcceptsSupportedProviderTypes(t *testing.T) {
+	for _, providerType := range []string{"litellm", "ollama", "openrouter"} {
+		cfg := validConfig()
+		p := cfg.AI.Providers["default"]
+		p.Type = providerType
+		cfg.AI.Providers["default"] = p
+		if err := cfg.Validate(); err != nil {
+			t.Fatalf("Validate %s error = %v", providerType, err)
+		}
 	}
 }

-func TestValidateRejectsInvalidProvider(t *testing.T) {
+func TestValidateRejectsInvalidProviderType(t *testing.T) {
 	cfg := validConfig()
-	cfg.AI.Provider = "unknown"
+	p := cfg.AI.Providers["default"]
+	p.Type = "unknown"
+	cfg.AI.Providers["default"] = p

 	if err := cfg.Validate(); err == nil {
-		t.Fatal("Validate() error = nil, want error for unsupported provider")
+		t.Fatal("Validate() error = nil, want error for unsupported provider type")
+	}
+}
+
+func TestValidateRejectsChainWithUnknownProvider(t *testing.T) {
+	cfg := validConfig()
+	cfg.AI.Metadata.Primary = RoleTarget{Provider: "does-not-exist", Model: "x"}
+
+	if err := cfg.Validate(); err == nil {
+		t.Fatal("Validate() error = nil, want error for chain referencing unknown provider")
+	}
+}
+
+func TestValidateRejectsEmptyProviders(t *testing.T) {
+	cfg := validConfig()
+	cfg.AI.Providers = map[string]ProviderConfig{}
+
+	if err := cfg.Validate(); err == nil {
+		t.Fatal("Validate() error = nil, want error for empty providers")
 	}
 }