feat: add database tables and API routes for agentic chat feature (#17570)

Backend portion of experimental `AgenticChat` feature:
- Adds database tables for chats and chat messages
- Adds functionality to stream messages from LLM providers using
`kylecarbs/aisdk-go`
- Adds API routes with relevant functionality (list, create, update
chats, insert chat message)
- Adds experiment `codersdk.AgenticChat`

---------

Co-authored-by: Kyle Carberry <kyle@carberry.com>

cli/server.go

@@ -61,6 +61,7 @@ import (
 	"github.com/coder/serpent"
 	"github.com/coder/wgtunnel/tunnelsdk"
 
+	"github.com/coder/coder/v2/coderd/ai"
 	"github.com/coder/coder/v2/coderd/entitlements"
 	"github.com/coder/coder/v2/coderd/notifications/reports"
 	"github.com/coder/coder/v2/coderd/runtimeconfig"
@@ -610,6 +611,22 @@ func (r *RootCmd) Server(newAPI func(context.Context, *coderd.Options) (*coderd.
 				)
 			}
 
+			aiProviders, err := ReadAIProvidersFromEnv(os.Environ())
+			if err != nil {
+				return xerrors.Errorf("read ai providers from env: %w", err)
+			}
+			vals.AI.Value.Providers = append(vals.AI.Value.Providers, aiProviders...)
+			for _, provider := range aiProviders {
+				logger.Debug(
+					ctx, "loaded ai provider",
+					slog.F("type", provider.Type),
+				)
+			}
+			languageModels, err := ai.ModelsFromConfig(ctx, vals.AI.Value.Providers)
+			if err != nil {
+				return xerrors.Errorf("create language models: %w", err)
+			}
+
 			realIPConfig, err := httpmw.ParseRealIPConfig(vals.ProxyTrustedHeaders, vals.ProxyTrustedOrigins)
 			if err != nil {
 				return xerrors.Errorf("parse real ip config: %w", err)
@@ -640,6 +657,7 @@ func (r *RootCmd) Server(newAPI func(context.Context, *coderd.Options) (*coderd.
 				CacheDir:                    cacheDir,
 				GoogleTokenValidator:        googleTokenValidator,
 				ExternalAuthConfigs:         externalAuthConfigs,
+				LanguageModels:              languageModels,
 				RealIPConfig:                realIPConfig,
 				SSHKeygenAlgorithm:          sshKeygenAlgorithm,
 				TracerProvider:              tracerProvider,
@@ -2621,6 +2639,77 @@ func redirectHTTPToHTTPSDeprecation(ctx context.Context, logger slog.Logger, inv
 	}
 }
 
+func ReadAIProvidersFromEnv(environ []string) ([]codersdk.AIProviderConfig, error) {
+	// The index numbers must be in-order.
+	sort.Strings(environ)
+
+	var providers []codersdk.AIProviderConfig
+	for _, v := range serpent.ParseEnviron(environ, "CODER_AI_PROVIDER_") {
+		tokens := strings.SplitN(v.Name, "_", 2)
+		if len(tokens) != 2 {
+			return nil, xerrors.Errorf("invalid env var: %s", v.Name)
+		}
+
+		providerNum, err := strconv.Atoi(tokens[0])
+		if err != nil {
+			return nil, xerrors.Errorf("parse number: %s", v.Name)
+		}
+
+		var provider codersdk.AIProviderConfig
+		switch {
+		case len(providers) < providerNum:
+			return nil, xerrors.Errorf(
+				"provider num %v skipped: %s",
+				len(providers),
+				v.Name,
+			)
+		case len(providers) == providerNum:
+			// At the next next provider.
+			providers = append(providers, provider)
+		case len(providers) == providerNum+1:
+			// At the current provider.
+			provider = providers[providerNum]
+		}
+
+		key := tokens[1]
+		switch key {
+		case "TYPE":
+			provider.Type = v.Value
+		case "API_KEY":
+			provider.APIKey = v.Value
+		case "BASE_URL":
+			provider.BaseURL = v.Value
+		case "MODELS":
+			provider.Models = strings.Split(v.Value, ",")
+		}
+		providers[providerNum] = provider
+	}
+	for _, envVar := range environ {
+		tokens := strings.SplitN(envVar, "=", 2)
+		if len(tokens) != 2 {
+			continue
+		}
+		switch tokens[0] {
+		case "OPENAI_API_KEY":
+			providers = append(providers, codersdk.AIProviderConfig{
+				Type:   "openai",
+				APIKey: tokens[1],
+			})
+		case "ANTHROPIC_API_KEY":
+			providers = append(providers, codersdk.AIProviderConfig{
+				Type:   "anthropic",
+				APIKey: tokens[1],
+			})
+		case "GOOGLE_API_KEY":
+			providers = append(providers, codersdk.AIProviderConfig{
+				Type:   "google",
+				APIKey: tokens[1],
+			})
+		}
+	}
+	return providers, nil
+}
+
 // ReadExternalAuthProvidersFromEnv is provided for compatibility purposes with
 // the viper CLI.
 func ReadExternalAuthProvidersFromEnv(environ []string) ([]codersdk.ExternalAuthConfig, error) {