Fix empty filtered runs passing

src/reporters/terminal.ts

@@ -18,6 +18,9 @@ export function renderRunTerminal(run: RunResult): string {
   lines.push(bold(`\nevalgate - ${run.suite}`));
   lines.push(dim(`${run.timestamp}`));
   lines.push("");
+  if (run.total === 0) {
+    lines.push(red("No cases matched the filter."));
+  }
 
   for (const cse of run.cases) {
     const mark = cse.passed ? green("PASS") : red("FAIL");

src/runner.ts

@@ -146,7 +146,8 @@ export async function runSuite(suite: EvalSuite, options: RunOptions = {}): Prom
   const costUsd = caseResults.reduce((s, r) => s + r.costUsd, 0);
 
   const thresholdMet = suite.threshold === undefined || meanScore >= suite.threshold;
-  const passed = thresholdMet && passedCount === total;
+  // A filtered run with no cases must fail instead of silently disabling the gate.
+  const passed = total > 0 && thresholdMet && passedCount === total;
 
   return {
     version: RESULT_VERSION,

tests/reporters.test.ts

@@ -34,6 +34,11 @@ describe("reporters", () => {
     expect(md).toContain("| Case | Base | Head | Delta | Change |");
   });
 
+  it("terminal reports explain when filtering selected no cases", async () => {
+    const run = await runSuite(suite, { filterTags: ["does-not-exist"] });
+    expect(renderRunTerminal(run)).toContain("No cases matched the filter");
+  });
+
   it("terminal reports render without throwing", async () => {
     const run = await runSuite(suite);
     expect(renderRunTerminal(run)).toContain("evalgate");

tests/runner.test.ts

@@ -63,6 +63,13 @@ describe("runSuite", () => {
     expect(res.cases[0]!.id).toBe("ok");
   });
 
+  it("fails when tag filtering selects no cases", async () => {
+    const suiteWithoutThreshold: EvalSuite = { ...suite, threshold: undefined };
+    const res = await runSuite(suiteWithoutThreshold, { filterTags: ["does-not-exist"] });
+    expect(res.total).toBe(0);
+    expect(res.passed).toBe(false);
+  });
+
   it("fires the onCase callback per case", async () => {
     const seen: string[] = [];
     await runSuite(suite, { onCase: (c) => seen.push(c.id) });