fix(coverage): measure operational trace helpers

src/index.ts

@@ -133,7 +133,6 @@ const trustedHeaderValuePattern = /^[A-Za-z0-9._:-]+$/;
 const clientIdentifierPattern = /^[A-Za-z0-9.:%_,-]+$/;
 const maxTrustedHeaderLength = 128;
 
-/* v8 ignore start */
 function jsonResponse(body: StandardErrorResponse | StandardSuccessResponse<unknown>, status = 200): Response {
   return new Response(JSON.stringify(body), {
     status,
@@ -159,6 +158,7 @@ function traceIdFromRequest(request: Request): string {
     || crypto.randomUUID();
 }
 
+/* v8 ignore start */
 function safeHash(input: string): string {
   let hash = 2166136261;
   for (let i = 0; i < input.length; i += 1) {

test/coverage-ignore-operational-helpers.test.ts

@@ -0,0 +1,19 @@
+import { readFileSync } from "node:fs";
+import { describe, expect, it } from "vitest";
+
+const source = readFileSync(new URL("../src/index.ts", import.meta.url), "utf8");
+const ignoredRegions = [...source.matchAll(/\/\* v8 ignore start \*\/[\s\S]*?\/\* v8 ignore stop \*\//g)]
+  .map((match) => match[0]);
+
+describe("operational helper coverage exclusions", () => {
+  it.each([
+    "jsonResponse",
+    "trustedTraceHeader",
+    "traceIdFromRequest",
+  ])("keeps %s inside measured production coverage", (functionName) => {
+    expect(
+      ignoredRegions.some((region) => region.includes(`function ${functionName}`)),
+      `${functionName} must not be hidden by a broad v8 ignore region`,
+    ).toBe(false);
+  });
+});

test/trace-header-coverage.test.ts

@@ -0,0 +1,31 @@
+import { describe, expect, it } from "vitest";
+import worker, { type Env } from "../src/index";
+
+const env = {} as Env;
+
+describe("trace header selection", () => {
+  it("uses a valid request id as the response trace identity", async () => {
+    const response = await worker.fetch(new Request("https://noema.example/health", {
+      headers: { "x-request-id": "request.trace-123" },
+    }), env);
+
+    expect(response.status).toBe(200);
+    const payload = await response.json() as { trace_id: string };
+    expect(payload.trace_id).toBe("request.trace-123");
+    expect(response.headers.get("x-trace-id")).toBe("request.trace-123");
+  });
+
+  it("falls back to a valid correlation id when request id contains unsafe characters", async () => {
+    const response = await worker.fetch(new Request("https://noema.example/health", {
+      headers: {
+        "x-request-id": "unsafe request id",
+        "x-correlation-id": "correlation:trace_456",
+      },
+    }), env);
+
+    expect(response.status).toBe(200);
+    const payload = await response.json() as { trace_id: string };
+    expect(payload.trace_id).toBe("correlation:trace_456");
+    expect(response.headers.get("x-trace-id")).toBe("correlation:trace_456");
+  });
+});