fix: round lighthouse category scores and show unscored categories as n/a (#2924)

The `lighthouse_audit` text summary formatted each category score as
`(score ?? 0) * 100`. That had two problems:

- A `null` category score, which Lighthouse uses for "not scored", was
printed as `0`, so it looked the same as a real score of 0 (#2915).
- Fractional scores showed floating-point noise, e.g. `0.57` printed as
`56.99999999999999` (#2916).

The summary now prints `Math.round(score * 100)`, which matches how the
Lighthouse report renders category scores, and prints `n/a` for a `null`
score. Structured content (`structuredContent.lighthouseResult`) is
unchanged and still carries the raw scores, including `null`. The text
summary is the only place these scores are formatted.

Testing:
- Added a `McpResponse` unit test and snapshot covering `0.57` → `57`, a
real `0` → `0`, and `null` → `n/a`, plus a check that the structured
content keeps the raw `0.57`/`0`/`null`. The new test fails on the old
code.
- `tests/McpResponse.test.ts` and `tests/tools/lighthouse.test.ts` pass
locally.
- `npm run check-format` passes, and `npm run gen` leaves no diff.

Fixes #2915
Fixes #2916

src/McpResponse.ts

@@ -1174,9 +1174,11 @@ Call ${handleDialog(this.#args).name} to handle it before continuing.`);
       response.push(`URL: ${summary.url}`);
       response.push('### Category Scores');
       for (const score of summary.scores) {
-        response.push(
-          `- ${score.title}: ${(score.score ?? 0) * 100} (${score.id})`,
-        );
+        // Lighthouse uses a null score for categories that could not be
+        // scored and renders scores as Math.round(score * 100).
+        const formattedScore =
+          score.score === null ? 'n/a' : Math.round(score.score * 100);
+        response.push(`- ${score.title}: ${formattedScore} (${score.id})`);
       }
       response.push('### Audit Summary');
       response.push(`Passed: ${summary.audits.passed}`);

tests/McpResponse.test.js.snapshot

@@ -1367,6 +1367,64 @@ exports[`lighthouse > includes lighthouse report paths 2`] = `
 }
 `;
 
+exports[`lighthouse > rounds category scores and shows unscored categories as n/a 1`] = `
+## Lighthouse Audit Results
+Mode: navigation
+Device: desktop
+URL: https://example.com
+### Category Scores
+- Accessibility: 57 (accessibility)
+- SEO: 0 (seo)
+- Agentic Browsing: n/a (agentic-browsing)
+### Audit Summary
+Passed: 10
+Failed: 1
+Total Timing: 1000ms
+### Reports
+- /tmp/report.json
+- /tmp/report.html
+`;
+
+exports[`lighthouse > rounds category scores and shows unscored categories as n/a 2`] = `
+{
+  "lighthouseResult": {
+    "summary": {
+      "mode": "navigation",
+      "device": "desktop",
+      "url": "https://example.com",
+      "scores": [
+        {
+          "id": "accessibility",
+          "title": "Accessibility",
+          "score": 0.57
+        },
+        {
+          "id": "seo",
+          "title": "SEO",
+          "score": 0
+        },
+        {
+          "id": "agentic-browsing",
+          "title": "Agentic Browsing",
+          "score": null
+        }
+      ],
+      "audits": {
+        "failed": 1,
+        "passed": 10
+      },
+      "timing": {
+        "total": 1000
+      }
+    },
+    "reports": [
+      "/tmp/report.json",
+      "/tmp/report.html"
+    ]
+  }
+}
+`;
+
 exports[`third-party developer tools > lists third-party developer tools 1`] = `
 ## Third-party developer tools
 My Tool Group: A group of tools

tests/McpResponse.test.ts

@@ -930,6 +930,54 @@ describe('lighthouse', () => {
       t.assert.snapshot(stabilizeStructuredContent(structuredContent));
     });
   });
+
+  it('rounds category scores and shows unscored categories as n/a', async t => {
+    await withMcpContext(async (response, context) => {
+      const lighthouseResult = {
+        summary: {
+          mode: 'navigation',
+          device: 'desktop',
+          url: 'https://example.com',
+          scores: [
+            {
+              id: 'accessibility',
+              title: 'Accessibility',
+              score: 0.57,
+            },
+            {
+              id: 'seo',
+              title: 'SEO',
+              score: 0,
+            },
+            {
+              id: 'agentic-browsing',
+              title: 'Agentic Browsing',
+              score: null,
+            },
+          ],
+          audits: {
+            failed: 1,
+            passed: 10,
+          },
+          timing: {
+            total: 1000,
+          },
+        },
+        reports: ['/tmp/report.json', '/tmp/report.html'],
+      };
+
+      response.attachLighthouseResult(lighthouseResult);
+      const {content, structuredContent} = await response.handle(context);
+
+      const text = getTextContent(content[0]);
+      assert.ok(text.includes('- Accessibility: 57 (accessibility)'));
+      assert.ok(text.includes('- SEO: 0 (seo)'));
+      assert.ok(text.includes('- Agentic Browsing: n/a (agentic-browsing)'));
+
+      t.assert.snapshot(text);
+      t.assert.snapshot(stabilizeStructuredContent(structuredContent));
+    });
+  });
 });
 
 describe('third-party developer tools', () => {