feat(routing): implement routing decision pipeline — M4-006

Add RoutingEngineService that classifies tasks, evaluates routing rules
in priority order, checks provider health, and applies a Sonnet → Haiku
→ Ollama fallback chain when no healthy rule match is found.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/gateway/src/agent/routing/routing-engine.service.ts

@@ -0,0 +1,216 @@
+import { Inject, Injectable, Logger } from '@nestjs/common';
+import { routingRules, type Db, and, asc, eq, or } from '@mosaic/db';
+import { DB } from '../../database/database.module.js';
+import { ProviderService } from '../provider.service.js';
+import { classifyTask } from './task-classifier.js';
+import type {
+  RoutingCondition,
+  RoutingRule,
+  RoutingDecision,
+  TaskClassification,
+} from './routing.types.js';
+
+// ─── Injection tokens ────────────────────────────────────────────────────────
+
+export const PROVIDER_SERVICE = Symbol('ProviderService');
+
+// ─── Fallback chain ──────────────────────────────────────────────────────────
+
+/**
+ * Ordered fallback providers tried when no rule matches or all matched
+ * providers are unhealthy.
+ */
+const FALLBACK_CHAIN: Array<{ provider: string; model: string }> = [
+  { provider: 'anthropic', model: 'claude-sonnet-4-6' },
+  { provider: 'anthropic', model: 'claude-haiku-4-5' },
+  { provider: 'ollama', model: 'llama3.2' },
+];
+
+// ─── Service ─────────────────────────────────────────────────────────────────
+
+@Injectable()
+export class RoutingEngineService {
+  private readonly logger = new Logger(RoutingEngineService.name);
+
+  constructor(
+    @Inject(DB) private readonly db: Db,
+    @Inject(ProviderService) private readonly providerService: ProviderService,
+  ) {}
+
+  /**
+   * Classify the message, evaluate routing rules in priority order, and return
+   * the best routing decision.
+   *
+   * @param message       - Raw user message text used for classification.
+   * @param userId        - Optional user ID for loading user-scoped rules.
+   * @param availableProviders - Optional pre-fetched provider health map to
+   *                       avoid redundant health checks inside tight loops.
+   */
+  async resolve(
+    message: string,
+    userId?: string,
+    availableProviders?: Record<string, { status: string }>,
+  ): Promise<RoutingDecision> {
+    const classification = classifyTask(message);
+    this.logger.debug(
+      `Classification: taskType=${classification.taskType} complexity=${classification.complexity} domain=${classification.domain}`,
+    );
+
+    // Load health data once (re-use caller-supplied map if provided)
+    const health = availableProviders ?? (await this.providerService.healthCheckAll());
+
+    // Load all applicable rules ordered by priority
+    const rules = await this.loadRules(userId);
+
+    // Evaluate rules in priority order
+    for (const rule of rules) {
+      if (!rule.enabled) continue;
+
+      if (!this.matchConditions(rule, classification)) continue;
+
+      const providerStatus = health[rule.action.provider]?.status;
+      const isHealthy = providerStatus === 'up' || providerStatus === 'ok';
+
+      if (!isHealthy) {
+        this.logger.debug(
+          `Rule "${rule.name}" matched but provider "${rule.action.provider}" is unhealthy (status: ${providerStatus ?? 'unknown'})`,
+        );
+        continue;
+      }
+
+      this.logger.debug(
+        `Rule matched: "${rule.name}" → ${rule.action.provider}/${rule.action.model}`,
+      );
+
+      return {
+        provider: rule.action.provider,
+        model: rule.action.model,
+        agentConfigId: rule.action.agentConfigId,
+        ruleName: rule.name,
+        reason: `Matched routing rule "${rule.name}"`,
+      };
+    }
+
+    // No rule matched (or all matched providers were unhealthy) — apply fallback chain
+    this.logger.debug('No rule matched; applying fallback chain');
+    return this.applyFallbackChain(health);
+  }
+
+  /**
+   * Check whether all conditions of a rule match the given task classification.
+   * An empty conditions array always matches (catch-all / fallback rule).
+   */
+  matchConditions(
+    rule: Pick<RoutingRule, 'conditions'>,
+    classification: TaskClassification,
+  ): boolean {
+    if (rule.conditions.length === 0) return true;
+
+    return rule.conditions.every((condition) => this.evaluateCondition(condition, classification));
+  }
+
+  // ─── Private helpers ───────────────────────────────────────────────────────
+
+  private evaluateCondition(
+    condition: RoutingCondition,
+    classification: TaskClassification,
+  ): boolean {
+    // `costTier` is a valid condition field but is not part of TaskClassification
+    // (it is supplied via userOverrides / request context). Treat unknown fields as
+    // undefined so conditions referencing them simply do not match.
+    const fieldValue = (classification as unknown as Record<string, unknown>)[condition.field];
+
+    switch (condition.operator) {
+      case 'eq': {
+        // Scalar equality: field value must equal condition value (string)
+        if (typeof condition.value !== 'string') return false;
+        return fieldValue === condition.value;
+      }
+
+      case 'in': {
+        // Set membership: condition value (array) contains field value
+        if (!Array.isArray(condition.value)) return false;
+        return condition.value.includes(fieldValue as string);
+      }
+
+      case 'includes': {
+        // Array containment: field value (array) includes condition value (string)
+        if (!Array.isArray(fieldValue)) return false;
+        if (typeof condition.value !== 'string') return false;
+        return (fieldValue as string[]).includes(condition.value);
+      }
+
+      default:
+        return false;
+    }
+  }
+
+  /**
+   * Load routing rules from the database.
+   * System rules + user-scoped rules (when userId is provided) are returned,
+   * ordered by priority ascending.
+   */
+  private async loadRules(userId?: string): Promise<RoutingRule[]> {
+    const whereClause = userId
+      ? or(
+          eq(routingRules.scope, 'system'),
+          and(eq(routingRules.scope, 'user'), eq(routingRules.userId, userId)),
+        )
+      : eq(routingRules.scope, 'system');
+
+    const rows = await this.db
+      .select()
+      .from(routingRules)
+      .where(whereClause)
+      .orderBy(asc(routingRules.priority));
+
+    return rows.map((row) => ({
+      id: row.id,
+      name: row.name,
+      priority: row.priority,
+      scope: row.scope as 'system' | 'user',
+      userId: row.userId ?? undefined,
+      conditions: (row.conditions as unknown as RoutingCondition[]) ?? [],
+      action: row.action as unknown as {
+        provider: string;
+        model: string;
+        agentConfigId?: string;
+        systemPromptOverride?: string;
+        toolAllowlist?: string[];
+      },
+      enabled: row.enabled,
+    }));
+  }
+
+  /**
+   * Walk the fallback chain and return the first healthy provider/model pair.
+   * If none are healthy, return the first entry unconditionally (last resort).
+   */
+  private applyFallbackChain(health: Record<string, { status: string }>): RoutingDecision {
+    for (const candidate of FALLBACK_CHAIN) {
+      const providerStatus = health[candidate.provider]?.status;
+      const isHealthy = providerStatus === 'up' || providerStatus === 'ok';
+      if (isHealthy) {
+        this.logger.debug(`Fallback resolved: ${candidate.provider}/${candidate.model}`);
+        return {
+          provider: candidate.provider,
+          model: candidate.model,
+          ruleName: 'fallback',
+          reason: `Fallback chain — no matching rule; selected ${candidate.provider}/${candidate.model}`,
+        };
+      }
+    }
+
+    // All providers in the fallback chain are unhealthy — use the first entry
+    const lastResort = FALLBACK_CHAIN[0]!;
+    this.logger.warn(
+      `All fallback providers unhealthy; using last resort: ${lastResort.provider}/${lastResort.model}`,
+    );
+    return {
+      provider: lastResort.provider,
+      model: lastResort.model,
+      ruleName: 'fallback',
+      reason: `Fallback chain exhausted (all providers unhealthy); using ${lastResort.provider}/${lastResort.model}`,
+    };
+  }
+}

apps/gateway/src/agent/routing/routing-engine.test.ts

@@ -0,0 +1,460 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { RoutingEngineService } from './routing-engine.service.js';
+import type { RoutingRule, TaskClassification } from './routing.types.js';
+
+// ─── Helpers ─────────────────────────────────────────────────────────────────
+
+function makeRule(
+  overrides: Partial<RoutingRule> &
+    Pick<RoutingRule, 'name' | 'priority' | 'conditions' | 'action'>,
+): RoutingRule {
+  return {
+    id: overrides.id ?? crypto.randomUUID(),
+    scope: 'system',
+    enabled: true,
+    ...overrides,
+  };
+}
+
+function makeClassification(overrides: Partial<TaskClassification> = {}): TaskClassification {
+  return {
+    taskType: 'conversation',
+    complexity: 'simple',
+    domain: 'general',
+    requiredCapabilities: [],
+    ...overrides,
+  };
+}
+
+/** Build a minimal RoutingEngineService with mocked DB and ProviderService. */
+function makeService(
+  rules: RoutingRule[] = [],
+  healthMap: Record<string, { status: string }> = {},
+): RoutingEngineService {
+  const mockDb = {
+    select: vi.fn().mockReturnValue({
+      from: vi.fn().mockReturnValue({
+        where: vi.fn().mockReturnValue({
+          orderBy: vi.fn().mockResolvedValue(
+            rules.map((r) => ({
+              id: r.id,
+              name: r.name,
+              priority: r.priority,
+              scope: r.scope,
+              userId: r.userId ?? null,
+              conditions: r.conditions,
+              action: r.action,
+              enabled: r.enabled,
+              createdAt: new Date(),
+              updatedAt: new Date(),
+            })),
+          ),
+        }),
+      }),
+    }),
+  };
+
+  const mockProviderService = {
+    healthCheckAll: vi.fn().mockResolvedValue(healthMap),
+  };
+
+  // Inject mocked dependencies directly (bypass NestJS DI for unit tests)
+  const service = new (RoutingEngineService as unknown as new (
+    db: unknown,
+    ps: unknown,
+  ) => RoutingEngineService)(mockDb, mockProviderService);
+
+  return service;
+}
+
+// ─── matchConditions ──────────────────────────────────────────────────────────
+
+describe('RoutingEngineService.matchConditions', () => {
+  let service: RoutingEngineService;
+
+  beforeEach(() => {
+    service = makeService();
+  });
+
+  it('returns true for empty conditions array (catch-all rule)', () => {
+    const rule = makeRule({
+      name: 'fallback',
+      priority: 99,
+      conditions: [],
+      action: { provider: 'anthropic', model: 'claude-sonnet-4-6' },
+    });
+    expect(service.matchConditions(rule, makeClassification())).toBe(true);
+  });
+
+  it('matches eq operator on scalar field', () => {
+    const rule = makeRule({
+      name: 'coding',
+      priority: 1,
+      conditions: [{ field: 'taskType', operator: 'eq', value: 'coding' }],
+      action: { provider: 'anthropic', model: 'claude-opus-4-6' },
+    });
+    expect(service.matchConditions(rule, makeClassification({ taskType: 'coding' }))).toBe(true);
+    expect(service.matchConditions(rule, makeClassification({ taskType: 'conversation' }))).toBe(
+      false,
+    );
+  });
+
+  it('matches in operator: field value is in the condition array', () => {
+    const rule = makeRule({
+      name: 'simple or moderate',
+      priority: 2,
+      conditions: [{ field: 'complexity', operator: 'in', value: ['simple', 'moderate'] }],
+      action: { provider: 'anthropic', model: 'claude-haiku-4-5' },
+    });
+    expect(service.matchConditions(rule, makeClassification({ complexity: 'simple' }))).toBe(true);
+    expect(service.matchConditions(rule, makeClassification({ complexity: 'moderate' }))).toBe(
+      true,
+    );
+    expect(service.matchConditions(rule, makeClassification({ complexity: 'complex' }))).toBe(
+      false,
+    );
+  });
+
+  it('matches includes operator: field array includes the condition value', () => {
+    const rule = makeRule({
+      name: 'reasoning required',
+      priority: 3,
+      conditions: [{ field: 'requiredCapabilities', operator: 'includes', value: 'reasoning' }],
+      action: { provider: 'anthropic', model: 'claude-opus-4-6' },
+    });
+    expect(
+      service.matchConditions(rule, makeClassification({ requiredCapabilities: ['reasoning'] })),
+    ).toBe(true);
+    expect(
+      service.matchConditions(
+        rule,
+        makeClassification({ requiredCapabilities: ['tools', 'reasoning'] }),
+      ),
+    ).toBe(true);
+    expect(
+      service.matchConditions(rule, makeClassification({ requiredCapabilities: ['tools'] })),
+    ).toBe(false);
+    expect(service.matchConditions(rule, makeClassification({ requiredCapabilities: [] }))).toBe(
+      false,
+    );
+  });
+
+  it('requires ALL conditions to match (AND logic)', () => {
+    const rule = makeRule({
+      name: 'complex coding',
+      priority: 1,
+      conditions: [
+        { field: 'taskType', operator: 'eq', value: 'coding' },
+        { field: 'complexity', operator: 'eq', value: 'complex' },
+      ],
+      action: { provider: 'anthropic', model: 'claude-opus-4-6' },
+    });
+
+    // Both match
+    expect(
+      service.matchConditions(
+        rule,
+        makeClassification({ taskType: 'coding', complexity: 'complex' }),
+      ),
+    ).toBe(true);
+
+    // Only one matches
+    expect(
+      service.matchConditions(
+        rule,
+        makeClassification({ taskType: 'coding', complexity: 'simple' }),
+      ),
+    ).toBe(false);
+
+    // Neither matches
+    expect(
+      service.matchConditions(
+        rule,
+        makeClassification({ taskType: 'conversation', complexity: 'simple' }),
+      ),
+    ).toBe(false);
+  });
+
+  it('returns false for eq when condition value is an array (type mismatch)', () => {
+    const rule = makeRule({
+      name: 'bad eq',
+      priority: 1,
+      conditions: [{ field: 'taskType', operator: 'eq', value: ['coding', 'research'] }],
+      action: { provider: 'anthropic', model: 'claude-sonnet-4-6' },
+    });
+    expect(service.matchConditions(rule, makeClassification({ taskType: 'coding' }))).toBe(false);
+  });
+
+  it('returns false for includes when field is not an array', () => {
+    const rule = makeRule({
+      name: 'bad includes',
+      priority: 1,
+      conditions: [{ field: 'taskType', operator: 'includes', value: 'coding' }],
+      action: { provider: 'anthropic', model: 'claude-sonnet-4-6' },
+    });
+    // taskType is a string, not an array — should be false
+    expect(service.matchConditions(rule, makeClassification({ taskType: 'coding' }))).toBe(false);
+  });
+});
+
+// ─── resolve — priority ordering ─────────────────────────────────────────────
+
+describe('RoutingEngineService.resolve — priority ordering', () => {
+  it('selects the highest-priority matching rule', async () => {
+    // Rules are supplied in priority-ascending order, as the DB would return them.
+    const rules = [
+      makeRule({
+        name: 'high priority',
+        priority: 1,
+        conditions: [{ field: 'taskType', operator: 'eq', value: 'coding' }],
+        action: { provider: 'anthropic', model: 'claude-opus-4-6' },
+      }),
+      makeRule({
+        name: 'low priority',
+        priority: 10,
+        conditions: [{ field: 'taskType', operator: 'eq', value: 'coding' }],
+        action: { provider: 'openai', model: 'gpt-4o' },
+      }),
+    ];
+
+    const service = makeService(rules, { anthropic: { status: 'up' }, openai: { status: 'up' } });
+
+    const decision = await service.resolve('implement a function');
+    expect(decision.ruleName).toBe('high priority');
+    expect(decision.provider).toBe('anthropic');
+    expect(decision.model).toBe('claude-opus-4-6');
+  });
+
+  it('skips non-matching rules and picks first match', async () => {
+    const rules = [
+      makeRule({
+        name: 'research rule',
+        priority: 1,
+        conditions: [{ field: 'taskType', operator: 'eq', value: 'research' }],
+        action: { provider: 'openai', model: 'gpt-4o' },
+      }),
+      makeRule({
+        name: 'coding rule',
+        priority: 2,
+        conditions: [{ field: 'taskType', operator: 'eq', value: 'coding' }],
+        action: { provider: 'anthropic', model: 'claude-sonnet-4-6' },
+      }),
+    ];
+
+    const service = makeService(rules, { anthropic: { status: 'up' }, openai: { status: 'up' } });
+
+    const decision = await service.resolve('implement a function');
+    expect(decision.ruleName).toBe('coding rule');
+    expect(decision.provider).toBe('anthropic');
+  });
+});
+
+// ─── resolve — unhealthy provider fallback ────────────────────────────────────
+
+describe('RoutingEngineService.resolve — unhealthy provider handling', () => {
+  it('skips matched rule when provider is unhealthy, tries next rule', async () => {
+    const rules = [
+      makeRule({
+        name: 'primary rule',
+        priority: 1,
+        conditions: [{ field: 'taskType', operator: 'eq', value: 'coding' }],
+        action: { provider: 'anthropic', model: 'claude-opus-4-6' },
+      }),
+      makeRule({
+        name: 'secondary rule',
+        priority: 2,
+        conditions: [{ field: 'taskType', operator: 'eq', value: 'coding' }],
+        action: { provider: 'openai', model: 'gpt-4o' },
+      }),
+    ];
+
+    const service = makeService(rules, {
+      anthropic: { status: 'down' }, // primary is unhealthy
+      openai: { status: 'up' },
+    });
+
+    const decision = await service.resolve('implement a function');
+    expect(decision.ruleName).toBe('secondary rule');
+    expect(decision.provider).toBe('openai');
+  });
+
+  it('falls back to Sonnet when all rules have unhealthy providers', async () => {
+    // Override the rule's provider to something unhealthy but keep anthropic up for fallback
+    const unhealthyRules = [
+      makeRule({
+        name: 'only rule',
+        priority: 1,
+        conditions: [{ field: 'taskType', operator: 'eq', value: 'coding' }],
+        action: { provider: 'openai', model: 'gpt-4o' }, // openai is unhealthy
+      }),
+    ];
+
+    const service2 = makeService(unhealthyRules, {
+      anthropic: { status: 'up' },
+      openai: { status: 'down' },
+    });
+
+    const decision = await service2.resolve('implement a function');
+    // Should fall through to Sonnet fallback on anthropic
+    expect(decision.provider).toBe('anthropic');
+    expect(decision.model).toBe('claude-sonnet-4-6');
+    expect(decision.ruleName).toBe('fallback');
+  });
+
+  it('falls back to Haiku when Sonnet provider is also down', async () => {
+    const rules: RoutingRule[] = []; // no rules
+
+    const service = makeService(rules, {
+      anthropic: { status: 'down' }, // Sonnet is on anthropic — down
+      ollama: { status: 'up' }, // Haiku is also on anthropic — use Ollama as next
+    });
+
+    const decision = await service.resolve('hello there');
+    // Sonnet (anthropic) is down, Haiku (anthropic) is down, Ollama is up
+    expect(decision.provider).toBe('ollama');
+    expect(decision.model).toBe('llama3.2');
+    expect(decision.ruleName).toBe('fallback');
+  });
+
+  it('uses last resort (Sonnet) when all fallback providers are unhealthy', async () => {
+    const rules: RoutingRule[] = [];
+
+    const service = makeService(rules, {
+      anthropic: { status: 'down' },
+      ollama: { status: 'down' },
+    });
+
+    const decision = await service.resolve('hello');
+    // All unhealthy — still returns first fallback entry as last resort
+    expect(decision.provider).toBe('anthropic');
+    expect(decision.model).toBe('claude-sonnet-4-6');
+    expect(decision.ruleName).toBe('fallback');
+  });
+});
+
+// ─── resolve — empty conditions (catch-all rule) ──────────────────────────────
+
+describe('RoutingEngineService.resolve — empty conditions (fallback rule)', () => {
+  it('matches catch-all rule for any message', async () => {
+    const rules = [
+      makeRule({
+        name: 'catch-all',
+        priority: 99,
+        conditions: [],
+        action: { provider: 'anthropic', model: 'claude-sonnet-4-6' },
+      }),
+    ];
+
+    const service = makeService(rules, { anthropic: { status: 'up' } });
+
+    const decision = await service.resolve('completely unrelated message xyz');
+    expect(decision.ruleName).toBe('catch-all');
+    expect(decision.provider).toBe('anthropic');
+    expect(decision.model).toBe('claude-sonnet-4-6');
+  });
+
+  it('catch-all is overridden by a higher-priority specific rule', async () => {
+    const rules = [
+      makeRule({
+        name: 'specific coding rule',
+        priority: 1,
+        conditions: [{ field: 'taskType', operator: 'eq', value: 'coding' }],
+        action: { provider: 'anthropic', model: 'claude-opus-4-6' },
+      }),
+      makeRule({
+        name: 'catch-all',
+        priority: 99,
+        conditions: [],
+        action: { provider: 'anthropic', model: 'claude-haiku-4-5' },
+      }),
+    ];
+
+    const service = makeService(rules, { anthropic: { status: 'up' } });
+
+    const codingDecision = await service.resolve('implement a function');
+    expect(codingDecision.ruleName).toBe('specific coding rule');
+    expect(codingDecision.model).toBe('claude-opus-4-6');
+
+    const conversationDecision = await service.resolve('hello how are you');
+    expect(conversationDecision.ruleName).toBe('catch-all');
+    expect(conversationDecision.model).toBe('claude-haiku-4-5');
+  });
+});
+
+// ─── resolve — disabled rules ─────────────────────────────────────────────────
+
+describe('RoutingEngineService.resolve — disabled rules', () => {
+  it('skips disabled rules', async () => {
+    const rules = [
+      makeRule({
+        name: 'disabled rule',
+        priority: 1,
+        enabled: false,
+        conditions: [{ field: 'taskType', operator: 'eq', value: 'coding' }],
+        action: { provider: 'anthropic', model: 'claude-opus-4-6' },
+      }),
+      makeRule({
+        name: 'enabled fallback',
+        priority: 99,
+        conditions: [],
+        action: { provider: 'anthropic', model: 'claude-sonnet-4-6' },
+      }),
+    ];
+
+    const service = makeService(rules, { anthropic: { status: 'up' } });
+
+    const decision = await service.resolve('implement a function');
+    expect(decision.ruleName).toBe('enabled fallback');
+    expect(decision.model).toBe('claude-sonnet-4-6');
+  });
+});
+
+// ─── resolve — pre-fetched health map ────────────────────────────────────────
+
+describe('RoutingEngineService.resolve — availableProviders override', () => {
+  it('uses the provided health map instead of calling healthCheckAll', async () => {
+    const rules = [
+      makeRule({
+        name: 'coding rule',
+        priority: 1,
+        conditions: [{ field: 'taskType', operator: 'eq', value: 'coding' }],
+        action: { provider: 'anthropic', model: 'claude-opus-4-6' },
+      }),
+    ];
+
+    const mockHealthCheckAll = vi.fn().mockResolvedValue({});
+    const mockDb = {
+      select: vi.fn().mockReturnValue({
+        from: vi.fn().mockReturnValue({
+          where: vi.fn().mockReturnValue({
+            orderBy: vi.fn().mockResolvedValue(
+              rules.map((r) => ({
+                id: r.id,
+                name: r.name,
+                priority: r.priority,
+                scope: r.scope,
+                userId: r.userId ?? null,
+                conditions: r.conditions,
+                action: r.action,
+                enabled: r.enabled,
+                createdAt: new Date(),
+                updatedAt: new Date(),
+              })),
+            ),
+          }),
+        }),
+      }),
+    };
+    const mockProviderService = { healthCheckAll: mockHealthCheckAll };
+
+    const service = new (RoutingEngineService as unknown as new (
+      db: unknown,
+      ps: unknown,
+    ) => RoutingEngineService)(mockDb, mockProviderService);
+
+    const preSupplied = { anthropic: { status: 'up' } };
+    await service.resolve('implement a function', undefined, preSupplied);
+
+    expect(mockHealthCheckAll).not.toHaveBeenCalled();
+  });
+});