feat(session): persist model tier overrides per session

Store per-session config in SQLite and route /model and /reset through command fast-paths so channel sessions keep independent model selection across reconnects and restarts.

src/gateway/session-bridge.test.ts

@@ -9,6 +9,9 @@ const mockSession = {
   getHistory: vi.fn(() => []),
   clear: vi.fn(),
   replaceHistory: vi.fn(),
+  getConfig: vi.fn((_key: string) => undefined as string | undefined),
+  setConfig: vi.fn(),
+  deleteConfig: vi.fn(),
 };
 
 const mockSessionManager = {
@@ -48,9 +51,21 @@ function createBridge(): SessionBridge {
   });
 }
 
+function createBridgeWithConfig(config: SessionBridgeConfig['config']): SessionBridge {
+  return new SessionBridge({
+    sessionManager: mockSessionManager as unknown as SessionBridgeConfig['sessionManager'],
+    modelClient: mockModelClient,
+    systemPrompt: 'test prompt',
+    toolRegistry: mockToolRegistry as unknown as SessionBridgeConfig['toolRegistry'],
+    toolExecutor: mockToolExecutor as unknown as SessionBridgeConfig['toolExecutor'],
+    config,
+  });
+}
+
 describe('SessionBridge', () => {
   beforeEach(() => {
     vi.clearAllMocks();
+    mockSession.getConfig.mockImplementation((_key: string) => undefined);
   });
 
   it('connect assigns a connection ID', () => {
@@ -142,4 +157,78 @@ describe('SessionBridge', () => {
     expect(bridge.getAgent('conn-2')).toBeDefined();
     expect(bridge.connectionCount).toBe(1);
   });
+
+  it('loads model tier from per-session config when creating a session agent', () => {
+    mockSession.getConfig.mockImplementation((key: string) => (key === 'modelTier' ? 'local' : undefined));
+
+    const bridge = createBridgeWithConfig({
+      agents: {
+        primary_tier: 'default',
+        delegation: {
+          compaction: 'fast',
+          memory_extraction: 'fast',
+          classification: 'fast',
+          tool_summarisation: 'fast',
+          complex_reasoning: 'complex',
+        },
+        max_delegation_depth: 3,
+      },
+      compaction: { enabled: false },
+      models: { default: { provider: 'anthropic', model: 'claude-3-haiku' } },
+    } as any);
+
+    bridge.connect('conn-tier');
+    const agent = bridge.getAgent('conn-tier');
+    expect(agent?.getModelTier()).toBe('local');
+  });
+
+  it('keeps different sessions isolated by persisted model tier', () => {
+    const sessionById: Record<string, any> = {};
+    const localSessionManager = {
+      ...mockSessionManager,
+      getSession: vi.fn((frontend: string, sessionId: string) => {
+        const fullId = `${frontend}:${sessionId}`;
+        if (!sessionById[fullId]) {
+          const tier = fullId === 'ws:ws:conn-a' ? 'fast' : 'complex';
+          sessionById[fullId] = {
+            ...mockSession,
+            id: fullId,
+            getConfig: vi.fn((key: string) => (key === 'modelTier' ? tier : undefined)),
+          };
+        }
+        return sessionById[fullId];
+      }),
+    };
+
+    const bridge = new SessionBridge({
+      sessionManager: localSessionManager as unknown as SessionBridgeConfig['sessionManager'],
+      modelClient: mockModelClient,
+      systemPrompt: 'test prompt',
+      toolRegistry: mockToolRegistry as unknown as SessionBridgeConfig['toolRegistry'],
+      toolExecutor: mockToolExecutor as unknown as SessionBridgeConfig['toolExecutor'],
+      config: {
+        agents: {
+          primary_tier: 'default',
+          delegation: {
+            compaction: 'fast',
+            memory_extraction: 'fast',
+            classification: 'fast',
+            tool_summarisation: 'fast',
+            complex_reasoning: 'complex',
+          },
+          max_delegation_depth: 3,
+        },
+        compaction: { enabled: false },
+        models: { default: { provider: 'anthropic', model: 'claude-3-haiku' } },
+      } as any,
+    });
+
+    bridge.connect('conn-a');
+    bridge.connect('conn-b');
+    const agentA = bridge.getAgent('conn-a');
+    const agentB = bridge.getAgent('conn-b');
+
+    expect(agentA?.getModelTier()).toBe('fast');
+    expect(agentB?.getModelTier()).toBe('complex');
+  });
 });