FN-7079: Correct quarantine baseline reporting

Correct the velocity baseline to reflect an empty quarantine ledger and cover that report-only path.

- Update the published test velocity baseline quarantine totals, buckets, trend row, and #leads summary to zero.
- Add a regression test that regenerates the report from an empty live quarantine ledger without measuring lanes.
- Assert deletion-due and bucket rows stay zero and stale nonzero quarantine text is removed.

Files changed:
 docs/test-velocity-baseline.md                    | 10 ++--
 scripts/__tests__/test-velocity-baseline.test.mjs | 72 ++++++++++++++++++++++-
 2 files changed, 76 insertions(+), 6 deletions(-)

Fusion-Task-Id: FN-7079

Fusion-Task-Lineage: d641adc3-f991-4d95-bcb2-7b20bbfeb0bb

docs/test-velocity-baseline.md

@@ -16,7 +16,7 @@
 | Merge gate wall-time (`pnpm test:gate`) | 7.5s | -9.3s |
 | Boot smoke wall-time (`pnpm smoke:boot`) | 18.2s | -4.7s |
 | Changed-only test wall-time (`pnpm test`) | 9.4s | -10.2s |
-| Quarantine / flake count | 3 | +3 |
+| Quarantine / flake count | 0 | 0 |
 | Deletion-due quarantines | 0 | n/a |
 
 ## Measurement failures
@@ -56,7 +56,7 @@
 
 | Age bucket | Count |
 |---|---:|
-| 0-6 days | 3 |
+| 0-6 days | 0 |
 | 7-13 days | 0 |
 | deletion due (>=14 days) | 0 |
 | unknown/future | 0 |
@@ -72,15 +72,15 @@
 | Row | Captured at | Gate | Boot smoke | `pnpm test` | Quarantine count |
 |---|---|---:|---:|---:|---:|
 | Previous | 2026-06-23T18:43:21.941Z | 16.8s | 22.8s | 19.6s | 0 |
-| Latest | 2026-06-25T05:47:54.804Z | 7.5s | 18.2s | 9.4s | 3 |
-| Delta | — | -9.3s | -4.7s | -10.2s | +3 |
+| Latest | 2026-06-25T05:47:54.804Z | 7.5s | 18.2s | 9.4s | 0 |
+| Delta | — | -9.3s | -4.7s | -10.2s | 0 |
 
 _Future weekly rows append to `scripts/test-velocity-history.json`; compare the latest row against the previous row before posting to #leads._
 
 ## Post to #leads
 
 ```text
-FN-6612 weekly test velocity: gate 7.5s (-9.3s), boot smoke 18.2s (-4.7s), pnpm test 9.4s (-10.2s), quarantine ledger 3 (+3). Slowest file: packages/dashboard/app/components/__tests__/SettingsModal.test.tsx at 1m 01s. Deletion-due quarantines: 0.
+FN-6612 weekly test velocity: gate 7.5s (-9.3s), boot smoke 18.2s (-4.7s), pnpm test 9.4s (-10.2s), quarantine ledger 0 (0). Slowest file: packages/dashboard/app/components/__tests__/SettingsModal.test.tsx at 1m 01s. Deletion-due quarantines: 0.
 ```
 
 ## How to refresh

scripts/__tests__/test-velocity-baseline.test.mjs

@@ -1,6 +1,6 @@
 import { describe, it } from "node:test";
 import assert from "node:assert/strict";
-import { mkdtempSync, readFileSync, rmSync } from "node:fs";
+import { mkdirSync, mkdtempSync, readFileSync, rmSync, writeFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import path from "node:path";
 
@@ -40,6 +40,12 @@ function makeTimings(count = 25) {
   };
 }
 
+function writeJson(rootDir, relativePath, value) {
+  const fullPath = path.join(rootDir, relativePath);
+  mkdirSync(path.dirname(fullPath), { recursive: true });
+  writeFileSync(fullPath, `${JSON.stringify(value, null, 2)}\n`, "utf8");
+}
+
 describe("topSlowestFiles", () => {
   it("returns exactly 20 rows in descending duration order with package attribution and stable ties", () => {
     const rows = topSlowestFiles(makeTimings(), 20);
@@ -207,6 +213,70 @@ describe("main", () => {
     }
   });
 
+  it("renders zero quarantine figures from an empty live ledger in report-only mode", async () => {
+    const rootDir = tempRoot();
+    try {
+      writeJson(rootDir, "scripts/lib/test-quarantine.json", { entries: [] });
+      writeJson(rootDir, "scripts/test-velocity-history.json", {
+        entries: [
+          {
+            capturedAt: "2026-06-18T12:00:00.000Z",
+            gateMs: 10_000,
+            bootSmokeMs: 20_000,
+            testMs: 30_000,
+            quarantineCount: 0,
+            slowestTop20: [{ file: "packages/a/src/__tests__/slow.test.ts", package: "@pkg/a", ms: 9_000 }],
+            measurementFailures: [],
+          },
+          {
+            capturedAt: "2026-06-25T12:00:00.000Z",
+            gateMs: 7_000,
+            bootSmokeMs: 18_000,
+            testMs: 25_000,
+            quarantineCount: 0,
+            slowestTop20: [{ file: "packages/a/src/__tests__/slow.test.ts", package: "@pkg/a", ms: 9_000 }],
+            measurementFailures: [],
+          },
+        ],
+      });
+      mkdirSync(path.join(rootDir, "docs"), { recursive: true });
+      writeFileSync(
+        path.join(rootDir, "docs/test-velocity-baseline.md"),
+        "| Quarantine / flake count | 3 | +3 |\n| 0-6 days | 3 |\nquarantine ledger 3 (+3)\n",
+        "utf8",
+      );
+
+      const exitCode = await main(["--write-report"], {
+        rootDir,
+        stdout: nullStream(),
+        stderr: nullStream(),
+        now: new Date("2026-06-26T12:00:00.000Z"),
+        commandRunner: async (measurement) => {
+          throw new Error(`unexpected command: ${measurement.label}`);
+        },
+      });
+
+      assert.equal(exitCode, 0);
+      const report = readFileSync(path.join(rootDir, "docs/test-velocity-baseline.md"), "utf8");
+      assert.match(report, /\| Quarantine \/ flake count \| 0 \| 0 \|/);
+      assert.match(report, /\| Deletion-due quarantines \| 0 \| n\/a \|/);
+      assert.match(report, /\| 0-6 days \| 0 \|/);
+      assert.match(report, /\| 7-13 days \| 0 \|/);
+      assert.match(report, /\| deletion due \(>=14 days\) \| 0 \|/);
+      assert.match(report, /\| unknown\/future \| 0 \|/);
+      assert.match(report, /\| — \| — \| — \|/);
+      assert.match(report, /\| Latest \| 2026-06-25T12:00:00\.000Z \| 7\.0s \| 18\.0s \| 25\.0s \| 0 \|/);
+      assert.match(report, /\| Delta \| — \| -3\.0s \| -2\.0s \| -5\.0s \| 0 \|/);
+      assert.match(report, /quarantine ledger 0 \(0\)/);
+      assert.match(report, /Deletion-due quarantines: 0\./);
+      assert.doesNotMatch(report, /\| Quarantine \/ flake count \| [1-9]/);
+      assert.doesNotMatch(report, /\| (?:0-6 days|7-13 days|deletion due \(>=14 days\)|unknown\/future) \| [1-9]/);
+      assert.doesNotMatch(report, /quarantine ledger [1-9]/);
+    } finally {
+      rmSync(rootDir, { recursive: true, force: true });
+    }
+  });
+
   it("honors --skip-build-preflight while still measuring lanes", async () => {
     const rootDir = tempRoot();
     const calls = [];