fix(audit): require integer drift minimum sample thresholds

Enforce non-negative integer minCandidateSampledEvents/minBaselineSampledEvents in drift gate evaluation and CLI parsing; add regression coverage. Architecture/protocol diagrams reviewed and no updates were needed for this validation-only change.

src/audit/phase0BaselineDrift.test.ts

@@ -382,4 +382,49 @@ describe('phase0BaselineDrift', () => {
       minCandidateSampledEvents: -5,
     })).toThrow('minCandidateSampledEvents');
   });
+
+  it('rejects non-integer sampled-event minimum thresholds', () => {
+    const comparison = comparePhase0BaselineDrift({
+      sampled_event_count: 10,
+      summary: {
+        event_counts: {
+          run_state: 0,
+          run_cancel: 0,
+          reaction_match: 0,
+          reaction_skip: 0,
+        },
+        run_outcomes: {
+          overall: {
+            total_outcomes: 5,
+            complete: 4,
+            cancelled: 1,
+            error: 0,
+            cancel_requested: 0,
+            start: 5,
+            completion_rate_pct: 80,
+            cancel_rate_pct: 20,
+            error_rate_pct: 0,
+          },
+          by_channel: [],
+          by_session: [],
+        },
+        cancel_latency_ms: null,
+        reactions: {
+          matched: 0,
+          skipped: 0,
+          total: 0,
+          match_rate_pct: null,
+          skip_rate_pct: null,
+          skip_reasons: [],
+        },
+      },
+    });
+
+    expect(() => evaluatePhase0BaselineDriftGate(comparison, {
+      minCandidateSampledEvents: 10.5,
+    })).toThrow('minCandidateSampledEvents');
+    expect(() => evaluatePhase0BaselineDriftGate(comparison, {
+      minBaselineSampledEvents: 8.2,
+    })).toThrow('minBaselineSampledEvents');
+  });
 });

src/audit/phase0BaselineDrift.ts

@@ -80,6 +80,17 @@ function readThreshold(value: unknown, thresholdName: string): number | undefine
   return parsed;
 }
 
+function readIntegerThreshold(value: unknown, thresholdName: string): number | undefined {
+  const parsed = readThreshold(value, thresholdName);
+  if (parsed === undefined) {
+    return undefined;
+  }
+  if (!Number.isInteger(parsed)) {
+    throw new Error(`${thresholdName} must be an integer greater than or equal to 0.`);
+  }
+  return parsed;
+}
+
 function toPctDelta(baseline: number, candidate: number): number | null {
   if (!Number.isFinite(baseline) || baseline <= 0 || !Number.isFinite(candidate)) {
     return null;
@@ -166,7 +177,7 @@ export function evaluatePhase0BaselineDriftGate(
     });
   }
 
-  const minCandidateSampledEvents = readThreshold(thresholds.minCandidateSampledEvents, 'minCandidateSampledEvents');
+  const minCandidateSampledEvents = readIntegerThreshold(thresholds.minCandidateSampledEvents, 'minCandidateSampledEvents');
   if (typeof minCandidateSampledEvents === 'number') {
     criteria.push({
       criterion: 'candidate_sampled_events',
@@ -176,7 +187,7 @@ export function evaluatePhase0BaselineDriftGate(
     });
   }
 
-  const minBaselineSampledEvents = readThreshold(thresholds.minBaselineSampledEvents, 'minBaselineSampledEvents');
+  const minBaselineSampledEvents = readIntegerThreshold(thresholds.minBaselineSampledEvents, 'minBaselineSampledEvents');
   if (typeof minBaselineSampledEvents === 'number') {
     if (!baseline) {
       criteria.push({