feat: per-agent model routing — route different agents to different providers (#238)

* feat: add agentModels and agentRouting to SettingsSchema

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: add agentRouting module for per-agent provider resolution

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: thread providerOverride through OpenAI shim for per-agent routing

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: getAnthropicClient accepts providerOverride for agent routing

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: thread providerOverride through Options and queryModel calls

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: thread providerOverride through query loop and ToolUseContext

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* feat: resolve agent routing in runAgent and inject providerOverride

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* docs: add Agent Routing configuration guide to README

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* test: add unit tests for resolveAgentProvider + plaintext api_key note

- 15 tests covering priority chain (name > subagentType > default > null)
- normalize() case-insensitive and hyphen/underscore equivalence
- Edge cases: null settings, missing config sections, non-existent model
- README note about api_key stored in plaintext

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* security: address code review — SSRF, credential leak, key collision

- base_url schema now uses z.string().url() for SSRF mitigation
- Strip auth headers (Authorization, x-api-key, api-key) from
  defaultHeaders when providerOverride is active, preventing
  Anthropic credentials from leaking to third-party endpoints
- Warn on duplicate normalized routing keys to prevent silent shadowing
- providerOverride.apiKey is never logged (verified via grep)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: 冯俊辉 <fengjunhui@shiyanjia.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/utils/settings/types.ts

@@ -713,6 +713,27 @@ export const SettingsSchema = lazySchema(() =>
         .string()
         .optional()
         .describe('Advisor model for the server-side advisor tool.'),
+      agentModels: z
+        .record(
+          z.string(),
+          z.object({
+            base_url: z.string().url().describe('OpenAI-compatible API endpoint (must be https:// or http://)'),
+            api_key: z.string().describe('API key for this provider'),
+          }),
+        )
+        .optional()
+        .describe(
+          'Map of model name to provider connection info. ' +
+            'Example: { "deepseek-chat": { "base_url": "https://api.deepseek.com/v1", "api_key": "sk-xxx" } }',
+        ),
+      agentRouting: z
+        .record(z.string(), z.string())
+        .optional()
+        .describe(
+          'Map of agent identifier (subagent_type or team member name) to model name. ' +
+            'Use "default" key as fallback. Model name must exist in agentModels. ' +
+            'Example: { "Explore": "deepseek-chat", "general-purpose": "gpt-4o", "default": "gpt-4o" }',
+        ),
       fastMode: z
         .boolean()
         .optional()