feat(routing): support per-agent backend selection across native/external

README.md

@@ -331,6 +331,15 @@ backends:
 
 If multiple external backends are enabled, Flynn selects the first in this order: `codex` -> `claude_code` -> `opencode` -> `gemini`.
 
+You can also route specific named agents to a backend:
+
+```yaml
+agent_configs:
+  coder:
+    model_tier: complex
+    backend: codex   # native | codex | claude_code | opencode | gemini
+```
+
 ### Native Audio Support
 
 Voice messages from channels can be handled in two ways:

src/daemon/index.test.ts

@@ -1,7 +1,7 @@
 import { describe, expect, it } from 'vitest';
 
 import { configSchema } from '../config/schema.js';
-import { createConfiguredExternalBackend } from './index.js';
+import { createConfiguredExternalBackend, createConfiguredExternalBackends } from './index.js';
 
 describe('createConfiguredExternalBackend', () => {
   const base = configSchema.parse({
@@ -37,4 +37,19 @@ describe('createConfiguredExternalBackend', () => {
     const backend = createConfiguredExternalBackend(cfg);
     expect(backend?.name).toBe('gemini');
   });
+
+  it('returns all enabled external backends and the default priority selection', () => {
+    const cfg = {
+      ...base,
+      backends: {
+        ...base.backends,
+        codex: { enabled: true, path: '/usr/bin/codex' },
+        gemini: { enabled: true, path: '/usr/bin/gemini' },
+      },
+    };
+    const configured = createConfiguredExternalBackends(cfg);
+    expect(configured.defaultName).toBe('codex');
+    expect(configured.backends.codex?.name).toBe('codex');
+    expect(configured.backends.gemini?.name).toBe('gemini');
+  });
 });