@@ -42,6 +42,24 @@ describe("mergeLcov", () => {
 		expect(merged).not.toContain("DA:3,1")
 	})
 
+	it("treats a negative v8 branch delta as uncovered instead of failing the merge", () => {
+		// The v8 provider emits negative BRDA counts for short-circuit conditions
+		// (e.g. `freshState === "aborted" || signal?.aborted`), which previously
+		// aborted the CI coverage merge with "Invalid BRDA ... -3".
+		const merged = mergeLcov([
+			["core", report(new Set([1])).replace("BRDA:2,0,0,-", "BRDA:2,0,0,-3")],
+			["api", report(new Set([1, 2]))],
+		])
+
+		// The negative-delta branch merges to uncovered, and the positive
+		// duplicate from the other lane still wins the union.
+		expect(merged).toContain("BRDA:2,0,0,1")
+
+		const solo = mergeLcov([["core", report(new Set([1])).replace("BRDA:2,0,0,-", "BRDA:2,0,0,-3")]])
+		expect(solo).toContain("BRDA:2,0,0,-")
+		expect(solo).not.toContain("-3")
+	})
+
 	it("merges disjoint source records without changing their paths", () => {
 		const merged = mergeLcov([
 			["api", report(new Set([1])).replaceAll("src/example.ts", "src/api.ts")],
 
@@ -7,6 +7,16 @@ const parseCount = (value, description) => {
 	return count
 }
 
+// The v8 provider emits negative BRDA counts for short-circuit conditions, where
+// an uncovered inner branch range is subtracted from a covered outer one
+// (e.g. `a === X || b?.flag`). A negative delta means the branch was never taken
+// on its own, so clamp it to uncovered instead of failing the merge.
+const parseBranchCount = (value, description) => {
+	const count = Number(value)
+	if (!Number.isSafeInteger(count)) throw new Error(`Invalid ${description}: ${value}`)
+	return count > 0 ? count : 0
+}
+
 const mergeCount = (records, key, count) => records.set(key, Math.max(records.get(key) ?? 0, count))
 
 const parseLcov = (lcov, label) => {
@@ -48,7 +58,7 @@ const parseLcov = (lcov, label) => {
 		} else if (record && line.startsWith("BRDA:")) {
 			const [lineNumber, block, branch, taken] = line.slice(5).split(",")
 			const key = `${lineNumber},${block},${branch}`
-			const count = taken === "-" ? 0 : parseCount(taken, `BRDA for ${record.source}`)
+			const count = taken === "-" ? 0 : parseBranchCount(taken, `BRDA for ${record.source}`)
 			mergeCount(record.branches, key, count)
 		} else if (record && line.startsWith("DA:")) {
 			const [lineNumber, count, checksum] = line.slice(3).split(",")