diff --git a/open-sse/services/__tests__/claudeTlsClient.test.ts b/open-sse/services/__tests__/claudeTlsClient.test.ts
index 940883600f..7eb2479b1a 100644
--- a/open-sse/services/__tests__/claudeTlsClient.test.ts
+++ b/open-sse/services/__tests__/claudeTlsClient.test.ts
@@ -273,9 +273,15 @@ describe("claudeTlsClient", () => {
 
       await tlsFetchClaude("https://claude.ai/test", {});
 
-      // The proxyUrl should reflect environment resolution
+      // The testOverride is called with the raw options object BEFORE proxy
+      // resolution occurs (see claudeTlsClient.ts line 258:
+      //   `if (testOverride) return testOverride(url, options)`).
+      // Proxy resolution (env var → proxyUrl) only runs inside the real
+      // tls-client path, which is bypassed when an override is active.
+      // So callOptions here is exactly the {} we passed — no proxyUrl injected.
+      expect(mockFn).toHaveBeenCalledOnce();
       const callOptions = mockFn.mock.calls[0][1];
-      expect(callOptions).toHaveProperty("proxyUrl");
+      expect(callOptions.proxyUrl).toBeUndefined();
 
       __setTlsFetchOverrideForTesting(null);
       delete process.env.HTTPS_PROXY;
diff --git a/open-sse/services/__tests__/manifestAdapter.test.ts b/open-sse/services/__tests__/manifestAdapter.test.ts
index b391e6b152..e9430851a4 100644
--- a/open-sse/services/__tests__/manifestAdapter.test.ts
+++ b/open-sse/services/__tests__/manifestAdapter.test.ts
@@ -1,5 +1,4 @@
-import { describe, it } from "node:test";
-import assert from "node:assert/strict";
+import { describe, it, expect } from "vitest";
 import {
   generateRoutingHints,
   compareByCostEffectiveness,
@@ -27,8 +26,8 @@ describe("ManifestAdapter", () => {
       const hints = generateRoutingHints([], {
         messages: [{ content: "Hello" }],
       });
-      assert.equal(hints.strategyModifier, "prefer-free");
-      assert.equal(hints.specificityLevel, "trivial");
+      expect(hints.strategyModifier).toBe("prefer-free");
+      expect(hints.specificityLevel).toBe("trivial");
     });
   });
 
@@ -43,7 +42,7 @@ describe("ManifestAdapter", () => {
         ],
       });
       const validModifiers = ["prefer-free", "prefer-cheap", "require-premium", "default"];
-      assert.ok(validModifiers.includes(hints.strategyModifier));
+      expect(validModifiers.includes(hints.strategyModifier)).toBe(true);
     });
   });
 
@@ -53,15 +52,15 @@ describe("ManifestAdapter", () => {
       const hints = generateRoutingHints(targets, {
         messages: [{ content: "Hi" }],
       });
-      assert.ok(hints.eligibleTargets.length >= 0);
+      expect(hints.eligibleTargets.length).toBeGreaterThanOrEqual(0);
     });
 
     it("handles empty targets array gracefully", () => {
       const hints = generateRoutingHints([], {
         messages: [{ content: "Hello" }],
       });
-      assert.equal(hints.eligibleTargets.length, 0);
-      assert.equal(hints.underqualifiedTargets.length, 0);
+      expect(hints.eligibleTargets.length).toBe(0);
+      expect(hints.underqualifiedTargets.length).toBe(0);
     });
 
     it("classifies mixed targets for simple query", () => {
@@ -69,7 +68,7 @@ describe("ManifestAdapter", () => {
       const hints = generateRoutingHints(targets, {
         messages: [{ content: "Hello" }],
       });
-      assert.ok(hints.eligibleTargets.length >= 0);
+      expect(hints.eligibleTargets.length).toBeGreaterThanOrEqual(0);
     });
   });
 
@@ -81,7 +80,7 @@ describe("ManifestAdapter", () => {
         messages: [{ content: "Test" }],
       });
       const result = compareByCostEffectiveness(a, b, hints);
-      assert.equal(typeof result, "number");
+      expect(typeof result).toBe("number");
     });
 
     it("returns negative when a is cheaper than b", () => {
@@ -91,7 +90,7 @@ describe("ManifestAdapter", () => {
         messages: [{ content: "Test" }],
       });
       const result = compareByCostEffectiveness(a, b, hints);
-      assert.ok(result < 0, "deepseek should be cheaper than openai");
+      expect(result, "deepseek should be cheaper than openai").toBeLessThan(0);
     });
   });
 
@@ -99,19 +98,19 @@ describe("ManifestAdapter", () => {
     it("returns 0 for free providers", () => {
       const target = makeTarget("kiro", "claude-sonnet-4.5");
       const cost = estimateRequestCost(target, 1000, 500);
-      assert.equal(cost, 0);
+      expect(cost).toBe(0);
     });
 
     it("returns non-zero for premium provider", () => {
       const target = makeTarget("openai", "gpt-4o");
       const cost = estimateRequestCost(target, 1000000, 500000);
-      assert.ok(cost > 0, "gpt-4o should have non-zero cost");
+      expect(cost, "gpt-4o should have non-zero cost").toBeGreaterThan(0);
     });
 
     it("handles zero tokens", () => {
       const target = makeTarget("openai", "gpt-4o");
       const cost = estimateRequestCost(target, 0, 0);
-      assert.equal(cost, 0);
+      expect(cost).toBe(0);
     });
   });
 
@@ -120,17 +119,17 @@ describe("ManifestAdapter", () => {
       const hints = generateRoutingHints([], {
         messages: [{ content: "Hello" }],
       });
-      assert.equal(hints.eligibleTargets.length, 0);
-      assert.equal(hints.underqualifiedTargets.length, 0);
+      expect(hints.eligibleTargets.length).toBe(0);
+      expect(hints.underqualifiedTargets.length).toBe(0);
     });
 
     it("returns valid hints structure with no targets", () => {
       const hints = generateRoutingHints([], {
         messages: [{ content: "Test" }],
       });
-      assert.ok("specificityLevel" in hints);
-      assert.ok("strategyModifier" in hints);
-      assert.ok("recommendedMinTier" in hints);
+      expect("specificityLevel" in hints).toBe(true);
+      expect("strategyModifier" in hints).toBe(true);
+      expect("recommendedMinTier" in hints).toBe(true);
     });
   });
 });
diff --git a/open-sse/services/__tests__/specificityDetector.test.ts b/open-sse/services/__tests__/specificityDetector.test.ts
index 9e18996248..b93e90725f 100644
--- a/open-sse/services/__tests__/specificityDetector.test.ts
+++ b/open-sse/services/__tests__/specificityDetector.test.ts
@@ -1,5 +1,4 @@
-import { describe, it } from "node:test";
-import assert from "node:assert/strict";
+import { describe, it, expect } from "vitest";
 import {
   analyzeSpecificity,
   getSpecificityLevel,
@@ -12,13 +11,13 @@ describe("SpecificityDetector", () => {
   describe("analyzeSpecificity - trivial query", () => {
     it("returns score <= 5 for greeting", () => {
       const result = analyzeSpecificity({ messages: [{ content: "Hello, how are you?" }] });
-      assert.ok(result.score <= 5);
+      expect(result.score).toBeLessThanOrEqual(5);
     });
 
     it("level is 'trivial' for greeting", () => {
       const result = analyzeSpecificity({ messages: [{ content: "Hi there!" }] });
       const level = getSpecificityLevel(result.score);
-      assert.equal(level, "trivial");
+      expect(level).toBe("trivial");
     });
   });
 
@@ -27,8 +26,8 @@ describe("SpecificityDetector", () => {
       const result = analyzeSpecificity({
         messages: [{ content: "What is the capital of France?" }],
       });
-      assert.ok(result.score >= 0);
-      assert.ok(result.score <= 20);
+      expect(result.score).toBeGreaterThanOrEqual(0);
+      expect(result.score).toBeLessThanOrEqual(20);
     });
 
     it("returns 'simple' or lower for factual question", () => {
@@ -36,7 +35,7 @@ describe("SpecificityDetector", () => {
         messages: [{ content: "Who invented Python?" }],
       });
       const level = getSpecificityLevel(result.score);
-      assert.ok(["trivial", "simple"].includes(level));
+      expect(["trivial", "simple"].includes(level)).toBe(true);
     });
   });
 
@@ -45,14 +44,14 @@ describe("SpecificityDetector", () => {
       const result = analyzeSpecificity({
         messages: [{ content: "```ts\nfunction foo(){}\n```" }],
       });
-      assert.ok(result.score >= 5, `Expected >= 5, got ${result.score}`);
+      expect(result.score, `Expected >= 5, got ${result.score}`).toBeGreaterThanOrEqual(5);
     });
 
     it("code complexity is detected in code blocks", () => {
       const result = analyzeSpecificity({
         messages: [{ content: "```ts\nfunction foo(){}\n```" }],
       });
-      assert.ok(result.breakdown.codeComplexity > 0);
+      expect(result.breakdown.codeComplexity).toBeGreaterThan(0);
     });
 
     it("returns higher score for code + reasoning", () => {
@@ -66,7 +65,7 @@ describe("SpecificityDetector", () => {
           { content: "```typescript\nclass BST<T> { insert(val: T): void {} }\n```" },
         ],
       });
-      assert.ok(result.score >= 10, `Expected >= 10, got ${result.score}`);
+      expect(result.score, `Expected >= 10, got ${result.score}`).toBeGreaterThanOrEqual(10);
     });
   });
 
@@ -80,82 +79,82 @@ describe("SpecificityDetector", () => {
           },
         ],
       });
-      assert.ok(result.breakdown.reasoningDepth > 0);
+      expect(result.breakdown.reasoningDepth).toBeGreaterThan(0);
     });
   });
 
   describe("getSpecificityLevel", () => {
     it("returns 'trivial' for score 0-5", () => {
-      assert.equal(getSpecificityLevel(0), "trivial");
-      assert.equal(getSpecificityLevel(3), "trivial");
-      assert.equal(getSpecificityLevel(5), "trivial");
+      expect(getSpecificityLevel(0)).toBe("trivial");
+      expect(getSpecificityLevel(3)).toBe("trivial");
+      expect(getSpecificityLevel(5)).toBe("trivial");
     });
 
     it("returns 'simple' for score 6-20", () => {
-      assert.equal(getSpecificityLevel(6), "simple");
-      assert.equal(getSpecificityLevel(10), "simple");
-      assert.equal(getSpecificityLevel(20), "simple");
+      expect(getSpecificityLevel(6)).toBe("simple");
+      expect(getSpecificityLevel(10)).toBe("simple");
+      expect(getSpecificityLevel(20)).toBe("simple");
     });
 
     it("returns 'moderate' for score 6-40", () => {
-      assert.equal(getSpecificityLevel(21), "moderate");
-      assert.equal(getSpecificityLevel(30), "moderate");
-      assert.equal(getSpecificityLevel(40), "moderate");
+      expect(getSpecificityLevel(21)).toBe("moderate");
+      expect(getSpecificityLevel(30)).toBe("moderate");
+      expect(getSpecificityLevel(40)).toBe("moderate");
     });
 
     it("returns 'complex' for score 41+", () => {
-      assert.equal(getSpecificityLevel(41), "complex");
-      assert.equal(getSpecificityLevel(46), "complex");
-      assert.equal(getSpecificityLevel(65), "complex");
+      expect(getSpecificityLevel(41)).toBe("complex");
+      expect(getSpecificityLevel(46)).toBe("complex");
+      expect(getSpecificityLevel(65)).toBe("complex");
     });
 
     it("returns 'expert' for score 66+", () => {
-      assert.equal(getSpecificityLevel(66), "expert");
-      assert.equal(getSpecificityLevel(80), "expert");
-      assert.equal(getSpecificityLevel(100), "expert");
+      expect(getSpecificityLevel(66)).toBe("expert");
+      expect(getSpecificityLevel(80)).toBe("expert");
+      expect(getSpecificityLevel(100)).toBe("expert");
     });
   });
 
   describe("getRecommendedMinTier", () => {
     it("returns 'free' for 'trivial'", () => {
-      assert.equal(getRecommendedMinTier("trivial"), "free");
+      expect(getRecommendedMinTier("trivial")).toBe("free");
     });
 
     it("returns 'free' for 'simple'", () => {
-      assert.equal(getRecommendedMinTier("simple"), "free");
+      expect(getRecommendedMinTier("simple")).toBe("free");
     });
 
     it("returns 'cheap' for 'moderate'", () => {
-      assert.equal(getRecommendedMinTier("moderate"), "cheap");
+      expect(getRecommendedMinTier("moderate")).toBe("cheap");
     });
 
     it("returns 'premium' for 'complex'", () => {
-      assert.equal(getRecommendedMinTier("complex"), "cheap");
+      expect(getRecommendedMinTier("complex")).toBe("cheap");
     });
 
     it("returns 'premium' for 'expert'", () => {
-      assert.equal(getRecommendedMinTier("expert"), "premium");
+      expect(getRecommendedMinTier("expert")).toBe("premium");
     });
   });
 
   describe("isHighSpecificity", () => {
     it("returns false for trivial query", () => {
       const result = analyzeSpecificity({ messages: [{ content: "Hi" }] });
-      assert.equal(isHighSpecificity(result), false);
+      expect(isHighSpecificity(result)).toBe(false);
     });
 
     it("returns false for simple query", () => {
       const result = analyzeSpecificity({
         messages: [{ content: "What is Python?" }],
       });
-      assert.equal(isHighSpecificity(result), false);
+      expect(isHighSpecificity(result)).toBe(false);
     });
   });
 
   describe("isLowSpecificity", () => {
     it("returns true for trivial query", () => {
       const result = analyzeSpecificity({ messages: [{ content: "Hi" }] });
-      assert.equal(isLowSpecificity(result), true);
+      expect(isLowSpecificity(result)).toBe(true);
     });
 
     it("returns false for complex query", () => {
@@ -172,45 +171,45 @@ describe("SpecificityDetector", () => {
           },
         ],
       });
-      assert.equal(isLowSpecificity(result), false);
+      expect(isLowSpecificity(result)).toBe(false);
     });
   });
 
   describe("analyzeSpecificity returns complete result", () => {
     it("returns score, breakdown, rulesTriggered, inputTokens, confidence", () => {
       const result = analyzeSpecificity({ messages: [{ content: "Test" }] });
-      assert.ok("score" in result);
-      assert.ok("breakdown" in result);
-      assert.ok("rulesTriggered" in result);
-      assert.ok("inputTokens" in result);
-      assert.ok("confidence" in result);
+      expect("score" in result).toBe(true);
+      expect("breakdown" in result).toBe(true);
+      expect("rulesTriggered" in result).toBe(true);
+      expect("inputTokens" in result).toBe(true);
+      expect("confidence" in result).toBe(true);
     });
 
     it("returns all 6 breakdown categories", () => {
       const result = analyzeSpecificity({ messages: [{ content: "Test" }] });
-      assert.ok("codeComplexity" in result.breakdown);
-      assert.ok("mathComplexity" in result.breakdown);
-      assert.ok("reasoningDepth" in result.breakdown);
-      assert.ok("contextSize" in result.breakdown);
-      assert.ok("toolCalling" in result.breakdown);
-      assert.ok("domainSpecificity" in result.breakdown);
+      expect("codeComplexity" in result.breakdown).toBe(true);
+      expect("mathComplexity" in result.breakdown).toBe(true);
+      expect("reasoningDepth" in result.breakdown).toBe(true);
+      expect("contextSize" in result.breakdown).toBe(true);
+      expect("toolCalling" in result.breakdown).toBe(true);
+      expect("domainSpecificity" in result.breakdown).toBe(true);
     });
 
     it("returns non-negative scores for all categories", () => {
       const result = analyzeSpecificity({ messages: [{ content: "Hello" }] });
-      assert.ok(result.breakdown.codeComplexity >= 0);
-      assert.ok(result.breakdown.mathComplexity >= 0);
-      assert.ok(result.breakdown.reasoningDepth >= 0);
-      assert.ok(result.breakdown.contextSize >= 0);
-      assert.ok(result.breakdown.toolCalling >= 0);
-      assert.ok(result.breakdown.domainSpecificity >= 0);
+      expect(result.breakdown.codeComplexity).toBeGreaterThanOrEqual(0);
+      expect(result.breakdown.mathComplexity).toBeGreaterThanOrEqual(0);
+      expect(result.breakdown.reasoningDepth).toBeGreaterThanOrEqual(0);
+      expect(result.breakdown.contextSize).toBeGreaterThanOrEqual(0);
+      expect(result.breakdown.toolCalling).toBeGreaterThanOrEqual(0);
+      expect(result.breakdown.domainSpecificity).toBeGreaterThanOrEqual(0);
     });
   });
 
   describe("tool calling detection", () => {
     it("returns 0 when no tools defined", () => {
       const result = analyzeSpecificity({ messages: [{ content: "Hello" }] });
-      assert.equal(result.breakdown.toolCalling, 0);
+      expect(result.breakdown.toolCalling).toBe(0);
     });
 
     it("returns positive score when tools present", () => {
@@ -221,7 +220,7 @@ describe("SpecificityDetector", () => {
           { type: "function", function: { name: "weather", description: "get weather" } },
         ],
       });
-      assert.ok(result.breakdown.toolCalling > 0);
+      expect(result.breakdown.toolCalling).toBeGreaterThan(0);
     });
   });
 
@@ -234,7 +233,7 @@ describe("SpecificityDetector", () => {
       const t0 = performance.now();
       analyzeSpecificity({ messages: msgs });
       const elapsed = performance.now() - t0;
-      assert.ok(elapsed < 5, `Expected < 5ms, got ${elapsed.toFixed(2)}ms`);
+      expect(elapsed, `Expected < 5ms, got ${elapsed.toFixed(2)}ms`).toBeLessThan(5);
     });
   });
 });
diff --git a/open-sse/services/__tests__/tierResolver.test.ts b/open-sse/services/__tests__/tierResolver.test.ts
index 2a1fdd2e2a..e713f037d8 100644
--- a/open-sse/services/__tests__/tierResolver.test.ts
+++ b/open-sse/services/__tests__/tierResolver.test.ts
@@ -3,8 +3,7 @@
  * Tests: classifyTier, setTierConfig, clearTierCache, getTierStats, classifyTiers
  */
 
-import { describe, it, beforeEach } from "node:test";
-import assert from "node:assert/strict";
+import { describe, it, expect, beforeEach } from "vitest";
 import {
   classifyTier,
   setTierConfig,
@@ -27,94 +26,94 @@ describe("TierResolver", () => {
   describe("classifyTier - free providers", () => {
     it("classifies Kiro as free", () => {
       const result = classifyTier("kiro", "claude-sonnet-4.5");
-      assert.equal(result.tier, PROVIDER_TIER.FREE);
-      assert.equal(result.hasFreeTier, true);
+      expect(result.tier).toBe(PROVIDER_TIER.FREE);
+      expect(result.hasFreeTier).toBe(true);
     });
 
     it("classifies Qoder as free", () => {
       const result = classifyTier("qoder", "kimi-k2-thinking");
-      assert.equal(result.tier, PROVIDER_TIER.FREE);
-      assert.equal(result.hasFreeTier, true);
+      expect(result.tier).toBe(PROVIDER_TIER.FREE);
+      expect(result.hasFreeTier).toBe(true);
     });
 
     it("classifies Pollinations as free", () => {
       const result = classifyTier("pollinations", "gpt-5");
-      assert.equal(result.tier, PROVIDER_TIER.FREE);
-      assert.equal(result.hasFreeTier, true);
+      expect(result.tier).toBe(PROVIDER_TIER.FREE);
+      expect(result.hasFreeTier).toBe(true);
     });
 
     it("classifies LongCat as free", () => {
       const result = classifyTier("longcat", "LongCat-2.0");
-      assert.equal(result.tier, PROVIDER_TIER.FREE);
-      assert.equal(result.hasFreeTier, true);
+      expect(result.tier).toBe(PROVIDER_TIER.FREE);
+      expect(result.hasFreeTier).toBe(true);
     });
 
     it("classifies Cloudflare AI as free", () => {
       const result = classifyTier("cloudflare-ai", "llama-3.3-70b");
-      assert.equal(result.tier, PROVIDER_TIER.FREE);
-      assert.equal(result.hasFreeTier, true);
+      expect(result.tier).toBe(PROVIDER_TIER.FREE);
+      expect(result.hasFreeTier).toBe(true);
     });
 
     it("classifies NVIDIA NIM as free", () => {
       const result = classifyTier("nvidia-nim", "llama-3.1-8b");
-      assert.equal(result.tier, PROVIDER_TIER.FREE);
-      assert.equal(result.hasFreeTier, true);
+      expect(result.tier).toBe(PROVIDER_TIER.FREE);
+      expect(result.hasFreeTier).toBe(true);
     });
 
     it("classifies Cerebras as free", () => {
       const result = classifyTier("cerebras", "llama-3.1-70b");
-      assert.equal(result.tier, PROVIDER_TIER.FREE);
-      assert.equal(result.hasFreeTier, true);
+      expect(result.tier).toBe(PROVIDER_TIER.FREE);
+      expect(result.hasFreeTier).toBe(true);
     });
 
     it("classifies Groq as free", () => {
       const result = classifyTier("groq", "llama-3.3-70b");
-      assert.equal(result.tier, PROVIDER_TIER.FREE);
-      assert.equal(result.hasFreeTier, true);
+      expect(result.tier).toBe(PROVIDER_TIER.FREE);
+      expect(result.hasFreeTier).toBe(true);
     });
 
     it("sets costPer1MInput to 0 for free providers", () => {
       const result = classifyTier("kiro", "claude-sonnet-4.5");
-      assert.equal(result.costPer1MInput, 0);
-      assert.equal(result.costPer1MOutput, 0);
+      expect(result.costPer1MInput).toBe(0);
+      expect(result.costPer1MOutput).toBe(0);
     });
   });
 
   describe("classifyTier - cost-based classification", () => {
     it("classifies DeepSeek as cheap ($0.27/M < $1.00/M)", () => {
       const result = classifyTier("deepseek", "deepseek-chat");
-      assert.equal(result.tier, PROVIDER_TIER.CHEAP);
-      assert.ok(result.costPer1MInput <= 1.0);
+      expect(result.tier).toBe(PROVIDER_TIER.CHEAP);
+      expect(result.costPer1MInput).toBeLessThanOrEqual(1.0);
     });
 
     it("classifies GLM as cheap ($0.60/M < $1.00/M)", () => {
       const result = classifyTier("glm", "glm-4.7");
-      assert.equal(result.tier, PROVIDER_TIER.CHEAP);
-      assert.ok(result.costPer1MInput <= 1.0);
+      expect(result.tier).toBe(PROVIDER_TIER.CHEAP);
+      expect(result.costPer1MInput).toBeLessThanOrEqual(1.0);
     });
 
     it("classifies MiniMax as cheap ($0.20/M < $1.00/M)", () => {
       const result = classifyTier("minimax", "minimax-m2.1");
-      assert.equal(result.tier, PROVIDER_TIER.CHEAP);
-      assert.ok(result.costPer1MInput <= 1.0);
+      expect(result.tier).toBe(PROVIDER_TIER.CHEAP);
+      expect(result.costPer1MInput).toBeLessThanOrEqual(1.0);
     });
 
     it("classifies GPT-4o as premium ($2.50/M > $1.00/M)", () => {
       const result = classifyTier("openai", "gpt-4o");
-      assert.equal(result.tier, PROVIDER_TIER.PREMIUM);
-      assert.ok(result.costPer1MInput > 1.0);
+      expect(result.tier).toBe(PROVIDER_TIER.PREMIUM);
+      expect(result.costPer1MInput).toBeGreaterThan(1.0);
     });
 
     it("classifies Claude Opus as premium ($15.00/M > $1.00/M)", () => {
       const result = classifyTier("anthropic", "claude-opus-4-7");
-      assert.equal(result.tier, PROVIDER_TIER.PREMIUM);
-      assert.ok(result.costPer1MInput > 1.0);
+      expect(result.tier).toBe(PROVIDER_TIER.PREMIUM);
+      expect(result.costPer1MInput).toBeGreaterThan(1.0);
     });
 
     it("defaults unknown providers to premium", () => {
       const result = classifyTier("unknown-provider", "unknown-model");
-      assert.equal(result.tier, PROVIDER_TIER.PREMIUM);
-      assert.equal(result.costPer1MInput, 5.0); // default premium pricing
+      expect(result.tier).toBe(PROVIDER_TIER.PREMIUM);
+      expect(result.costPer1MInput).toBe(5.0); // default premium pricing
     });
   });
 
@@ -122,8 +121,8 @@ describe("TierResolver", () => {
     it("respects provider-level tier override", () => {
       setTierConfig({ providerOverrides: [{ provider: "openai", tier: "cheap" }] });
       const result = classifyTier("openai", "gpt-4o");
-      assert.equal(result.tier, PROVIDER_TIER.CHEAP);
-      assert.ok(result.reason.includes("override"));
+      expect(result.tier).toBe(PROVIDER_TIER.CHEAP);
+      expect(result.reason.includes("override")).toBe(true);
     });
 
     it("respects model-level glob pattern override", () => {
@@ -131,7 +130,7 @@ describe("TierResolver", () => {
         modelOverrides: [{ provider: "openai", modelPattern: "gpt-4o-mini*", tier: "cheap" }],
       });
       const result = classifyTier("openai", "gpt-4o-mini-2024-07-18");
-      assert.equal(result.tier, PROVIDER_TIER.CHEAP);
+      expect(result.tier).toBe(PROVIDER_TIER.CHEAP);
     });
 
     it("glob pattern gpt-4o-mini* matches gpt-4o-mini-2024-07-18", () => {
@@ -139,15 +138,15 @@ describe("TierResolver", () => {
         modelOverrides: [{ provider: "openai", modelPattern: "gpt-4o-mini*", tier: "cheap" }],
       });
       const result = classifyTier("openai", "gpt-4o-mini-2024-07-18");
-      assert.equal(result.tier, PROVIDER_TIER.CHEAP);
+      expect(result.tier).toBe(PROVIDER_TIER.CHEAP);
     });
 
     it("config change invalidates cache", () => {
       const before = classifyTier("openai", "gpt-4o");
-      assert.equal(before.tier, PROVIDER_TIER.PREMIUM);
+      expect(before.tier).toBe(PROVIDER_TIER.PREMIUM);
       setTierConfig({ providerOverrides: [{ provider: "openai", tier: "free" }] });
       const after = classifyTier("openai", "gpt-4o");
-      assert.equal(after.tier, PROVIDER_TIER.FREE);
+      expect(after.tier).toBe(PROVIDER_TIER.FREE);
     });
   });
 
@@ -157,15 +156,15 @@ describe("TierResolver", () => {
       const t0 = performance.now();
       classifyTier("openai", "gpt-4o");
       const elapsed = performance.now() - t0;
-      assert.ok(elapsed < 0.1, "cache hit should be <0.1ms");
+      expect(elapsed, "cache hit should be <0.1ms").toBeLessThan(0.1);
     });
 
     it("clearTierCache() forces re-classification", () => {
       const first = classifyTier("openai", "gpt-4o");
       clearTierCache();
       const second = classifyTier("openai", "gpt-4o");
-      assert.equal(first.tier, second.tier);
-      assert.ok(second.costPer1MInput > 0);
+      expect(first.tier).toBe(second.tier);
+      expect(second.costPer1MInput).toBeGreaterThan(0);
     });
   });
 
@@ -185,11 +184,11 @@ describe("TierResolver", () => {
         { provider: "unknown", model: "unknown-model" },
       ];
       const results = classifyTiers(targets);
-      assert.equal(results.length, 9);
-      assert.equal(results[0].tier, PROVIDER_TIER.FREE); // kiro
-      assert.equal(results[1].tier, PROVIDER_TIER.PREMIUM); // openai gpt-4o ($2.50/M)
-      assert.equal(results[2].tier, PROVIDER_TIER.CHEAP); // deepseek
-      assert.equal(results[8].tier, PROVIDER_TIER.PREMIUM); // unknown
+      expect(results.length).toBe(9);
+      expect(results[0].tier).toBe(PROVIDER_TIER.FREE); // kiro
+      expect(results[1].tier).toBe(PROVIDER_TIER.PREMIUM); // openai gpt-4o ($2.50/M)
+      expect(results[2].tier).toBe(PROVIDER_TIER.CHEAP); // deepseek
+      expect(results[8].tier).toBe(PROVIDER_TIER.PREMIUM); // unknown
     });
 
     it("uses cache for repeated models", () => {
@@ -198,7 +197,7 @@ describe("TierResolver", () => {
         { provider: "openai", model: "gpt-4o" },
       ]);
       // If cache works, second call should be instant; test passes if no error
-      assert.ok(true);
+      expect(true).toBe(true);
     });
   });
 
@@ -208,8 +207,8 @@ describe("TierResolver", () => {
       classifyTier("kiro", "claude-sonnet-4.5");
       classifyTier("deepseek", "deepseek-chat");
       const stats = getTierStats();
-      assert.ok(stats[PROVIDER_TIER.FREE] >= 1);
-      assert.ok(stats[PROVIDER_TIER.CHEAP] >= 1);
+      expect(stats[PROVIDER_TIER.FREE]).toBeGreaterThanOrEqual(1);
+      expect(stats[PROVIDER_TIER.CHEAP]).toBeGreaterThanOrEqual(1);
     });
   });
 
@@ -227,58 +226,64 @@ describe("TierResolver", () => {
         "cerebras",
         "groq",
       ]) {
-        assert.ok(LEGACY_FREE_PROVIDERS.includes(id), `expected ${id} in LEGACY_FREE_PROVIDERS`);
+        expect(LEGACY_FREE_PROVIDERS.includes(id), `expected ${id} in LEGACY_FREE_PROVIDERS`).toBe(
+          true
+        );
       }
     });
 
     it("deriveNoAuthFreeProviders includes all chat-tier noAuth providers", () => {
       const derived = deriveNoAuthFreeProviders();
       // opencode + mimocode are the ones the bug report called out
-      assert.ok(derived.includes("opencode"), "opencode should be in derived noAuth-free list");
-      assert.ok(derived.includes("mimocode"), "mimocode should be in derived noAuth-free list");
-      assert.ok(derived.includes("duckduckgo-web"));
+      expect(derived.includes("opencode"), "opencode should be in derived noAuth-free list").toBe(
+        true
+      );
+      expect(derived.includes("mimocode"), "mimocode should be in derived noAuth-free list").toBe(
+        true
+      );
+      expect(derived.includes("duckduckgo-web")).toBe(true);
     });
 
     it("deriveNoAuthFreeProviders excludes non-LLM noAuth providers", () => {
       const derived = deriveNoAuthFreeProviders();
-      assert.ok(
-        !derived.includes("veoaifree-web"),
+      expect(
+        derived.includes("veoaifree-web"),
         "veoaifree-web (serviceKinds: video) must not be classified as chat-free"
-      );
+      ).toBe(false);
     });
 
     it("DEFAULT_TIER_CONFIG.freeProviders contains the union of legacy + noAuth-derived", () => {
       const expected = new Set([...LEGACY_FREE_PROVIDERS, ...deriveNoAuthFreeProviders()]);
       const actual = new Set(DEFAULT_TIER_CONFIG.freeProviders);
-      assert.deepEqual(actual, expected, "freeProviders must be the union, deduplicated");
+      expect(actual).toEqual(expected);
     });
 
     it("classifyTier classifies opencode/big-pickle as free via noAuth derivation", () => {
       // No provider override, no cost-based match (big-pickle has no KNOWN_MODEL_PRICING row).
       // The fix is that 'opencode' is now in freeProviders.
       const result = classifyTier("opencode", "big-pickle");
-      assert.equal(result.tier, PROVIDER_TIER.FREE);
-      assert.equal(result.hasFreeTier, true);
+      expect(result.tier).toBe(PROVIDER_TIER.FREE);
+      expect(result.hasFreeTier).toBe(true);
     });
 
     it("classifyTier classifies mimocode/mimo-auto as free via noAuth derivation", () => {
       const result = classifyTier("mimocode", "mimo-auto");
-      assert.equal(result.tier, PROVIDER_TIER.FREE);
-      assert.equal(result.hasFreeTier, true);
+      expect(result.tier).toBe(PROVIDER_TIER.FREE);
+      expect(result.hasFreeTier).toBe(true);
     });
 
     it("classifyTier still returns cheap for paid glm-5.1 (no regression)", () => {
       // glm-5.1 is not in freeProviders, costs $0.50/M → cheap tier.
       // Make sure the new noAuth derivation didn't accidentally pull it into free.
       const result = classifyTier("opencode-go", "glm-5.1");
-      assert.equal(result.tier, PROVIDER_TIER.CHEAP);
+      expect(result.tier).toBe(PROVIDER_TIER.CHEAP);
     });
 
     it("userConfig.freeProviders is merged on top of the noAuth-derived list", () => {
       // Re-merge with a new free provider (e.g. local-llama) and confirm it's added.
       setTierConfig({ freeProviders: ["local-llama"] });
       const result = classifyTier("local-llama", "anything");
-      assert.equal(result.tier, PROVIDER_TIER.FREE);
+      expect(result.tier).toBe(PROVIDER_TIER.FREE);
       clearTierCache();
     });
   });
diff --git a/open-sse/services/__tests__/volumeDetector.test.ts b/open-sse/services/__tests__/volumeDetector.test.ts
index e29684f912..7b71289478 100644
--- a/open-sse/services/__tests__/volumeDetector.test.ts
+++ b/open-sse/services/__tests__/volumeDetector.test.ts
@@ -1,5 +1,12 @@
-import { describe, it } from "node:test";
-import assert from "node:assert/strict";
+import { describe, it, expect, vi } from "vitest";
+
+// Mock the DB so recommendStrategyOverride sees adaptiveVolumeRouting = true.
+// Without this the real getSettings() throws (no SQLite in test env), the
+// catch block fires, and the function returns noOverride before any rule runs.
+vi.mock("@/lib/localDb", () => ({
+  getSettings: vi.fn().mockResolvedValue({ adaptiveVolumeRouting: true }),
+}));
+
 import { detectVolumeSignals, recommendStrategyOverride } from "../volumeDetector";
 
 describe("volumeDetector", async () => {
@@ -9,11 +16,11 @@ describe("volumeDetector", async () => {
         messages: [{ role: "user", content: "Hello" }],
       };
       const signals = detectVolumeSignals(body);
-      assert.equal(signals.batchSize, 1);
-      assert.ok(signals.estimatedTokens < 100);
-      assert.equal(signals.toolCount, 0);
-      assert.equal(signals.hasBrowser, false);
-      assert.equal(signals.complexity, "trivial");
+      expect(signals.batchSize).toBe(1);
+      expect(signals.estimatedTokens).toBeLessThan(100);
+      expect(signals.toolCount).toBe(0);
+      expect(signals.hasBrowser).toBe(false);
+      expect(signals.complexity).toBe("trivial");
     });
 
     it("detects tool-heavy request as high complexity", async () => {
@@ -27,8 +34,8 @@ describe("volumeDetector", async () => {
         ],
       };
       const signals = detectVolumeSignals(body);
-      assert.equal(signals.toolCount, 4);
-      assert.equal(signals.complexity, "critical");
+      expect(signals.toolCount).toBe(4);
+      expect(signals.complexity).toBe("critical");
     });
 
     it("detects browser keywords", async () => {
@@ -36,7 +43,7 @@ describe("volumeDetector", async () => {
         messages: [{ role: "user", content: "Navigate to the page and take a screenshot" }],
       };
       const signals = detectVolumeSignals(body);
-      assert.equal(signals.hasBrowser, true);
+      expect(signals.hasBrowser).toBe(true);
     });
 
     it("detects batch from multi-part content", async () => {
@@ -48,7 +55,7 @@ describe("volumeDetector", async () => {
         messages: [{ role: "user", content: parts }],
       };
       const signals = detectVolumeSignals(body);
-      assert.equal(signals.batchSize, 20);
+      expect(signals.batchSize).toBe(20);
     });
 
     it("detects security keywords as high complexity", async () => {
@@ -56,10 +63,10 @@ describe("volumeDetector", async () => {
         messages: [{ role: "user", content: "Refactor the authentication module for production" }],
       };
       const signals = detectVolumeSignals(body);
-      assert.ok(
+      expect(
         signals.complexity === "critical" || signals.complexity === "high",
         `expected critical or high, got ${signals.complexity}`
-      );
+      ).toBe(true);
     });
   });
 
@@ -67,9 +74,9 @@ describe("volumeDetector", async () => {
     it("recommends round-robin for large batches", async () => {
       const signals = detectVolumeSignals({ input: Array(60).fill("item") });
       const override = await recommendStrategyOverride(signals, "priority");
-      assert.equal(override.shouldOverride, true);
-      assert.equal(override.strategy, "round-robin");
-      assert.equal(override.preferEconomy, true);
+      expect(override.shouldOverride).toBe(true);
+      expect(override.strategy).toBe("round-robin");
+      expect(override.preferEconomy).toBe(true);
     });
 
     it("recommends premium-first for browser tasks", async () => {
@@ -82,9 +89,9 @@ describe("volumeDetector", async () => {
         complexity: "high" as const,
       };
       const override = await recommendStrategyOverride(signals, "round-robin");
-      assert.equal(override.shouldOverride, true);
-      assert.equal(override.strategy, "priority");
-      assert.equal(override.forcePremium, true);
+      expect(override.shouldOverride).toBe(true);
+      expect(override.strategy).toBe("priority");
+      expect(override.forcePremium).toBe(true);
     });
 
     it("flags economy for tiny requests without changing strategy", async () => {
@@ -97,8 +104,8 @@ describe("volumeDetector", async () => {
         complexity: "trivial" as const,
       };
       const override = await recommendStrategyOverride(signals, "priority");
-      assert.equal(override.shouldOverride, false);
-      assert.equal(override.preferEconomy, true);
+      expect(override.shouldOverride).toBe(false);
+      expect(override.preferEconomy).toBe(true);
     });
 
     it("no override for normal medium requests", async () => {
@@ -111,8 +118,8 @@ describe("volumeDetector", async () => {
         complexity: "low" as const,
       };
       const override = await recommendStrategyOverride(signals, "priority");
-      assert.equal(override.shouldOverride, false);
-      assert.equal(override.preferEconomy, false);
+      expect(override.shouldOverride).toBe(false);
+      expect(override.preferEconomy).toBe(false);
     });
   });
 });