feat(llm): provider base URLs come with sensible defaults

New llm.ApplyProviderDefaults fills base_url from env vars (OPENROUTER_BASE_URL,
CLAUDE_BRIDGE_URL, OLLAMA_BASE_URL) falling back to hardcoded values — so
standard Docker deployments can omit the field entirely in config.yaml. The
main.go dispatch and BuildBackendFactories both call it before constructing
providers.

claude-bridge's startup check relaxes from \"base_url required\" to \"api_key
required\" since the URL is now defaulted; users running the bridge on a
non-default host set CLAUDE_BRIDGE_URL.

Gemini ignores base_url (native endpoint is a const); keep for future
openai-compat proxy support only.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Alexey Panfilov

cmd/agent/main.go

@@ -63,6 +63,9 @@ func main() {
 		if name == "embedding" {
 			continue
 		}
+		// Fill in well-known defaults (base URLs etc.) so config entries can
+		// omit them. See llm.ApplyProviderDefaults for the policy.
+		mc = llm.ApplyProviderDefaults(mc)
 		switch mc.Provider {
 		case "openrouter":
 			if mc.APIKey == "" || mc.Model == "" {
@@ -83,7 +86,9 @@ func main() {
 			p, e := llm.NewOllama(mc)
 			addProvider(name, p, e)
 		case "claude-bridge":
-			if mc.BaseURL == "" {
+			// base_url now has a default (host.docker.internal:9900); api_key
+			// (bridge token) is still mandatory.
+			if mc.APIKey == "" {
 				continue
 			}
 			p, e := llm.NewClaudeBridge(mc)

internal/llm/defaults.go

@@ -0,0 +1,61 @@
+package llm
+
+import (
+	"os"
+
+	"telegram-agent/internal/config"
+)
+
+// Default base URLs for each provider type. The ones that never change
+// (OpenRouter, Google) are hardcoded; Docker-host-bound ones (Claude Bridge,
+// Ollama) read an env var first so non-Docker deployments can override.
+const (
+	DefaultOpenRouterBaseURL = "https://openrouter.ai/api/v1"
+	// GeminiNativeProvider has its own endpoint constant — this is only used
+	// if someone ever wires Gemini through an OpenAI-compat proxy.
+	DefaultGeminiOpenAIBaseURL = "https://generativelanguage.googleapis.com/v1beta/openai/"
+	// DefaultClaudeBridgeURL assumes bot-in-Docker + bridge-on-host; override
+	// with CLAUDE_BRIDGE_URL for other topologies.
+	DefaultClaudeBridgeURL = "http://host.docker.internal:9900"
+	DefaultOllamaBaseURL   = "http://host.docker.internal:11434"
+)
+
+// ApplyProviderDefaults fills in fields that have well-known defaults when
+// they're absent from the config entry. Returns a copy — the original is
+// never mutated so callers that keep cfg.Models references around don't
+// see surprise changes.
+//
+// Current defaults:
+//   - openrouter   → base_url = OPENROUTER_BASE_URL env or DefaultOpenRouterBaseURL
+//   - claude-bridge→ base_url = CLAUDE_BRIDGE_URL env or DefaultClaudeBridgeURL
+//   - ollama       → base_url = OLLAMA_BASE_URL env or DefaultOllamaBaseURL
+//   - gemini       → base_url is unused by the native provider (kept for the
+//     openai-compat variant only).
+//
+// Secrets (api_key) are NOT filled here — callers should already expand
+// ${ENV_VAR} before reaching this function.
+func ApplyProviderDefaults(cfg config.ModelConfig) config.ModelConfig {
+	if cfg.BaseURL != "" {
+		return cfg
+	}
+	switch cfg.Provider {
+	case "openrouter":
+		cfg.BaseURL = firstNonEmpty(os.Getenv("OPENROUTER_BASE_URL"), DefaultOpenRouterBaseURL)
+	case "claude-bridge":
+		cfg.BaseURL = firstNonEmpty(os.Getenv("CLAUDE_BRIDGE_URL"), DefaultClaudeBridgeURL)
+	case "ollama":
+		cfg.BaseURL = firstNonEmpty(os.Getenv("OLLAMA_BASE_URL"), DefaultOllamaBaseURL)
+	case "gemini":
+		// Native provider ignores BaseURL. Keep empty.
+	}
+	return cfg
+}
+
+func firstNonEmpty(vals ...string) string {
+	for _, v := range vals {
+		if v != "" {
+			return v
+		}
+	}
+	return ""
+}

internal/llm/factory.go

@@ -30,6 +30,7 @@ func BuildBackendFactories(cfg *config.Config) map[string]BackendFactory {
 		if seen[mc.Provider] {
 			continue
 		}
+		mc = ApplyProviderDefaults(mc)
 		switch mc.Provider {
 		case "openrouter":
 			base := mc