diff --git a/scripts/__tests__/run-vitest-watchdog.test.mjs b/scripts/__tests__/run-vitest-watchdog.test.mjs
index fa4c8411a6..3d9f4f791b 100644
--- a/scripts/__tests__/run-vitest-watchdog.test.mjs
+++ b/scripts/__tests__/run-vitest-watchdog.test.mjs
@@ -39,7 +39,9 @@ test("deriveBudgetMs: no fresh timing falls back to the per-class ceiling", () =
 
 test("deriveBudgetMs: fresh timing tightens within the band", () => {
   // expected×multiplier between floor and ceiling → use the tightened value.
-  const expected = 200_000; // 200s
+  // 300s × 3.5 = 1050s, which sits between the shard floor (15min) and
+  // ceiling (30min) so the tightened value is used un-clamped.
+  const expected = 300_000; // 300s
   const derived = deriveBudgetMs({ klass: "shard", expectedDurationMs: expected, timingsFresh: true });
   assert.equal(derived, Math.round(expected * DEFAULT_BUDGET_MULTIPLIER));
   assert.ok(derived >= CLASS_BUDGET_BANDS.shard.floor);
diff --git a/scripts/lib/run-vitest-watchdog.mjs b/scripts/lib/run-vitest-watchdog.mjs
index b047a70b07..362ca0623a 100644
--- a/scripts/lib/run-vitest-watchdog.mjs
+++ b/scripts/lib/run-vitest-watchdog.mjs
@@ -36,7 +36,17 @@ const MINUTE = 60_000;
  */
 export const CLASS_BUDGET_BANDS = {
   // One CI shard command (may fan out across several packages via --filter).
-  shard: { floor: 5 * MINUTE, ceiling: 30 * MINUTE },
+  // Floor is 15min, not 5min: the heaviest shard slices (@fusion/engine and
+  // @fusion/core, each split [1/2]+[2/2]) are import- and real-git-subprocess
+  // heavy, and the committed scripts/test-timings.json undercounts that
+  // overhead (most files bucket to the 100ms floor; the snapshot total is far
+  // below current wall-clock). A "fresh" but undercounting snapshot was
+  // tightening these slices to ~340-405s and SIGKILLing healthy runs on slower
+  // CI runners — the exact false-kill the band is meant to prevent (see the
+  // deriveBudgetMs note above and KTD-2). 15min sits comfortably above the
+  // observed CI need while still bounding a true hang far under the job's
+  // 60min ceiling. Mirrors the dashboard-lane heavy-lane floor.
+  shard: { floor: 15 * MINUTE, ceiling: 30 * MINUTE },
   // One local changed-file package invocation.
   changed: { floor: 2 * MINUTE, ceiling: 20 * MINUTE },
   // One dashboard quality lane (heap-managed). Matches the historical 15min.