feat(gateway): support full /model switching in webchat sessions

src/gateway/handlers/agent.test.ts

@@ -143,6 +143,82 @@ describe('createAgentHandlers command fast-path', () => {
     expect(((sent[0] as GatewayEvent).data as { content: string }).content).toContain('Switched to model tier: fast');
   });
 
+  it('handles /model <tier> <provider/model> in gateway sessions', async () => {
+    const sent: OutboundMessage[] = [];
+    const send = vi.fn((msg: OutboundMessage) => sent.push(msg));
+    const modelRouter = {
+      setClient: vi.fn(),
+      setTierStrict: vi.fn(),
+    };
+    const handlersWithRouter = createAgentHandlers({
+      sessionBridge: sessionBridge as unknown as AgentHandlerDeps['sessionBridge'],
+      laneQueue: new LaneQueue(),
+      sessionManager: sessionManager as unknown as AgentHandlerDeps['sessionManager'],
+      commandRegistry,
+      modelRouter: modelRouter as unknown as AgentHandlerDeps['modelRouter'],
+      runtimeConfig: {
+        models: {
+          default: { provider: 'anthropic', model: 'claude-sonnet-4' },
+          fallback_chain: ['anthropic'],
+        },
+      } as unknown as AgentHandlerDeps['runtimeConfig'],
+    });
+    const req: GatewayRequest = {
+      id: 9,
+      method: 'agent.send',
+      params: {
+        message: '/model default github/gpt-5-mini',
+        connectionId: 'conn-1',
+        metadata: { isCommand: true, command: 'model', commandArgs: 'default github/gpt-5-mini' },
+      },
+    };
+
+    await handlersWithRouter['agent.send'](req, send);
+
+    expect(modelRouter.setClient).toHaveBeenCalledWith('default', expect.anything(), 'github/gpt-5-mini');
+    expect(modelRouter.setTierStrict).toHaveBeenCalledWith('default', true);
+    expect(mockAgent.setModelTier).toHaveBeenCalledWith('default');
+    expect(((sent[0] as GatewayEvent).data as { content: string }).content).toContain('Set default to: github/gpt-5-mini');
+  });
+
+  it('handles /model <tier> reset in gateway sessions', async () => {
+    const sent: OutboundMessage[] = [];
+    const send = vi.fn((msg: OutboundMessage) => sent.push(msg));
+    const modelRouter = {
+      setClient: vi.fn(),
+      setTierStrict: vi.fn(),
+    };
+    const handlersWithRouter = createAgentHandlers({
+      sessionBridge: sessionBridge as unknown as AgentHandlerDeps['sessionBridge'],
+      laneQueue: new LaneQueue(),
+      sessionManager: sessionManager as unknown as AgentHandlerDeps['sessionManager'],
+      commandRegistry,
+      modelRouter: modelRouter as unknown as AgentHandlerDeps['modelRouter'],
+      runtimeConfig: {
+        models: {
+          default: { provider: 'anthropic', model: 'claude-sonnet-4' },
+          fallback_chain: ['anthropic'],
+        },
+      } as unknown as AgentHandlerDeps['runtimeConfig'],
+    });
+    const req: GatewayRequest = {
+      id: 10,
+      method: 'agent.send',
+      params: {
+        message: '/model default reset',
+        connectionId: 'conn-1',
+        metadata: { isCommand: true, command: 'model', commandArgs: 'default reset' },
+      },
+    };
+
+    await handlersWithRouter['agent.send'](req, send);
+
+    expect(modelRouter.setClient).toHaveBeenCalledWith('default', expect.anything(), 'anthropic/claude-sonnet-4');
+    expect(modelRouter.setTierStrict).toHaveBeenCalledWith('default', false);
+    expect(mockAgent.setModelTier).toHaveBeenCalledWith('default');
+    expect(((sent[0] as GatewayEvent).data as { content: string }).content).toContain('Reset default to: anthropic/claude-sonnet-4');
+  });
+
   it('falls through to agent.process for unknown commands', async () => {
     const sent: OutboundMessage[] = [];
     const send = vi.fn((msg: OutboundMessage) => sent.push(msg));