feat(agent): add provider switching and OAuth credential support

- Add getProviderInfo() and setProvider() methods to Agent class
- Expose provider methods via AsyncAgent
- Add setLlmProviderOAuthToken() for storing OAuth credentials
- Extend ProviderConfig type with OAuth fields (oauthToken, oauthRefreshToken, oauthExpiresAt)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/agent/async-agent.ts

@@ -221,4 +221,19 @@ export class AsyncAgent {
   getMessages(): AgentMessage[] {
     return this.agent.getMessages();
   }
+
+  /**
+   * Get current provider and model information.
+   */
+  getProviderInfo(): { provider: string; model: string | undefined } {
+    return this.agent.getProviderInfo();
+  }
+
+  /**
+   * Switch to a different provider and/or model.
+   * This updates the agent's model without recreating the session.
+   */
+  setProvider(providerId: string, modelId?: string): { provider: string; model: string | undefined } {
+    return this.agent.setProvider(providerId, modelId);
+  }
 }

src/agent/credentials.ts

@@ -1,11 +1,17 @@
-import { existsSync, readFileSync } from "node:fs";
-import { join } from "node:path";
+import { existsSync, readFileSync, writeFileSync, mkdirSync } from "node:fs";
+import { join, dirname } from "node:path";
 import { homedir } from "node:os";
 import JSON5 from "json5";
 import { DATA_DIR } from "../shared/paths.js";
 
 type ProviderConfig = {
+  // API Key authentication
   apiKey?: string | undefined;
+  // OAuth authentication
+  oauthToken?: string | undefined;
+  oauthRefreshToken?: string | undefined;
+  oauthExpiresAt?: number | undefined;
+  // Common
   baseUrl?: string | undefined;
   model?: string | undefined;
 };
@@ -223,6 +229,132 @@ export class CredentialManager {
     this.skillsConfig = null;
     this.resolvedSkillsEnv = null;
   }
+
+  /**
+   * Set the API key for a provider and save to credentials.json5.
+   * Creates the file if it doesn't exist.
+   */
+  setLlmProviderApiKey(provider: string, apiKey: string): void {
+    const path = getCredentialsPath();
+
+    // Load existing config or create new one
+    let config: CredentialsConfig = { version: 1 };
+    if (existsSync(path)) {
+      try {
+        const raw = readFileSync(path, "utf8");
+        config = JSON5.parse(raw) as CredentialsConfig;
+      } catch {
+        // If parse fails, start fresh
+        config = { version: 1 };
+      }
+    }
+
+    // Ensure structure exists
+    if (!config.llm) {
+      config.llm = {};
+    }
+    if (!config.llm.providers) {
+      config.llm.providers = {};
+    }
+
+    // Set or update the provider config
+    const existing = config.llm.providers[provider] ?? {};
+    config.llm.providers[provider] = {
+      ...existing,
+      apiKey,
+    };
+
+    // Write back to file
+    mkdirSync(dirname(path), { recursive: true });
+    const content = JSON.stringify(config, null, 2);
+    writeFileSync(path, content, "utf8");
+
+    // Reset cache so next read picks up the change
+    this.reset();
+  }
+
+  /**
+   * Set OAuth token for a provider and save to credentials.json5.
+   * Used for OAuth providers like claude-code and openai-codex.
+   */
+  setLlmProviderOAuthToken(
+    provider: string,
+    token: string,
+    refreshToken?: string,
+    expiresAt?: number,
+  ): void {
+    const path = getCredentialsPath();
+
+    // Load existing config or create new one
+    let config: CredentialsConfig = { version: 1 };
+    if (existsSync(path)) {
+      try {
+        const raw = readFileSync(path, "utf8");
+        config = JSON5.parse(raw) as CredentialsConfig;
+      } catch {
+        config = { version: 1 };
+      }
+    }
+
+    // Ensure structure exists
+    if (!config.llm) {
+      config.llm = {};
+    }
+    if (!config.llm.providers) {
+      config.llm.providers = {};
+    }
+
+    // Set or update the provider config
+    const existing = config.llm.providers[provider] ?? {};
+    config.llm.providers[provider] = {
+      ...existing,
+      oauthToken: token,
+      oauthRefreshToken: refreshToken,
+      oauthExpiresAt: expiresAt,
+    };
+
+    // Write back to file
+    mkdirSync(dirname(path), { recursive: true });
+    const content = JSON.stringify(config, null, 2);
+    writeFileSync(path, content, "utf8");
+
+    // Reset cache
+    this.reset();
+  }
+
+  /**
+   * Set the default LLM provider and save to credentials.json5.
+   */
+  setDefaultLlmProvider(provider: string): void {
+    const path = getCredentialsPath();
+
+    // Load existing config or create new one
+    let config: CredentialsConfig = { version: 1 };
+    if (existsSync(path)) {
+      try {
+        const raw = readFileSync(path, "utf8");
+        config = JSON5.parse(raw) as CredentialsConfig;
+      } catch {
+        config = { version: 1 };
+      }
+    }
+
+    // Ensure structure exists
+    if (!config.llm) {
+      config.llm = {};
+    }
+
+    // Set default provider
+    config.llm.provider = provider;
+
+    // Write back to file
+    mkdirSync(dirname(path), { recursive: true });
+    const content = JSON.stringify(config, null, 2);
+    writeFileSync(path, content, "utf8");
+
+    // Reset cache
+    this.reset();
+  }
 }
 
 export const credentialManager = new CredentialManager();

src/agent/runner.ts

@@ -9,6 +9,8 @@ import {
   resolveApiKeyForProvider,
   resolveBaseUrl,
   resolveModelId,
+  PROVIDER_ALIAS,
+  getDefaultModel,
 } from "./providers/index.js";
 import { SessionManager } from "./session/session-manager.js";
 import { ProfileManager } from "./profile/index.js";
@@ -82,7 +84,7 @@ export class Agent {
   private initialized = false;
 
   // Auth profile rotation state
-  private readonly resolvedProvider: string;
+  private resolvedProvider: string;
   private currentApiKey: string | undefined;
   private currentProfileId: string | undefined;
   private profileCandidates: string[];
@@ -598,6 +600,72 @@ export class Agent {
     this.profile?.updateStyle(style);
   }
 
+  /**
+   * Get current provider and model information.
+   */
+  getProviderInfo(): { provider: string; model: string | undefined } {
+    return {
+      provider: this.resolvedProvider,
+      model: this.agent.state.model?.id,
+    };
+  }
+
+  /**
+   * Switch to a different provider and/or model.
+   * This updates the agent's model without recreating the session.
+   */
+  setProvider(providerId: string, modelId?: string): { provider: string; model: string | undefined } {
+    // Resolve the actual provider (handle aliases like claude-code -> anthropic)
+    const actualProvider = PROVIDER_ALIAS[providerId] ?? providerId;
+
+    // Resolve the model
+    const targetModel = modelId ?? getDefaultModel(providerId) ?? getDefaultModel(actualProvider);
+    const model = resolveModel({ provider: providerId, model: targetModel });
+
+    if (!model) {
+      throw new Error(`Failed to resolve model for provider: ${providerId}, model: ${targetModel}`);
+    }
+
+    // Resolve API key for the new provider
+    // For OAuth providers (claude-code, openai-codex), we need to use the original providerId
+    // because OAuth credentials are resolved by the original provider name, not the alias
+    const resolved = resolveApiKeyForProvider(providerId);
+    if (resolved) {
+      this.currentApiKey = resolved.apiKey;
+      this.currentProfileId = resolved.profileId;
+    } else {
+      // Fallback: try with actual provider (for API key based providers)
+      this.currentApiKey = resolveApiKey(actualProvider);
+      this.currentProfileId = actualProvider;
+    }
+
+    if (!this.currentApiKey) {
+      throw new Error(`No API key configured for provider: ${providerId}`);
+    }
+
+    // Update the agent's model and API key
+    const baseUrl = resolveBaseUrl(actualProvider);
+    const modelWithBaseUrl = baseUrl ? { ...model, baseUrl } : model;
+    this.agent.setModel(modelWithBaseUrl);
+
+    // Update internal state
+    this.resolvedProvider = providerId;
+
+    // Update session metadata
+    this.session.saveMeta({
+      provider: actualProvider,
+      model: model.id,
+      thinkingLevel: this.agent.state.thinkingLevel,
+      reasoningMode: this.reasoningMode,
+      contextWindowTokens: this.contextWindowGuard.tokens,
+    });
+
+    return {
+      provider: providerId,
+      model: model.id,
+    };
+  }
+
   /**
    * Build the full system prompt using the structured builder.
    * Combines profile content, tools, skills, and runtime info.