fix(changelog): preserved released sections during auto-fix

Restored the released coding-agent changelog sections that the previous pre-publish fix run flattened into Unreleased. The local checkout only had tags through v15.5.15, so fix-changelogs compared against an old tag and promoted entire newly-added release sections.

- Kept newly-added release-section hunks out of collectPromotableAddedItemLines so the fixer still promotes individual new items added under an existing released section, but does not rewrite whole release blocks.
- Added regression coverage for the release-section case.
- Restored the coding-agent changelog history and kept only the #2582 entry under Unreleased.

Fixes #2582

scripts/fix-changelogs.test.ts

@@ -23,6 +23,27 @@ describe("collectPromotableAddedItemLines", () => {
 
 		expect(lines.get("packages/example/CHANGELOG.md")).toEqual(new Set([12, 33]));
 	});
+
+	it("does not promote items from newly added release sections", () => {
+		const diff = [
+			"diff --git a/packages/example/CHANGELOG.md b/packages/example/CHANGELOG.md",
+			"--- a/packages/example/CHANGELOG.md",
+			"+++ b/packages/example/CHANGELOG.md",
+			"@@ -1,0 +1,8 @@",
+			"+# Changelog",
+			"+",
+			"+## [1.0.0] - 2026-01-01",
+			"+",
+			"+### Fixed",
+			"+",
+			"+- Released fix.",
+			"+- Another released fix.",
+		].join("\n");
+
+		const lines = collectPromotableAddedItemLines(diff);
+
+		expect(lines.get("packages/example/CHANGELOG.md")).toBeUndefined();
+	});
 });
 
 describe("fixChangelogContent", () => {

scripts/fix-changelogs.ts

@@ -425,6 +425,10 @@ export function fixChangelogContent(
 function hunkKey(hunk: HunkRef): string {
 	return `${hunk.path}\0${hunk.index}`;
 }
+function isAddedReleaseHeadingLine(line: string): boolean {
+	return line.startsWith("+## [");
+}
+
 
 function itemKey(pathName: string, text: string): string {
 	return `${pathName}\0${normalizeItemText(text)}`;
@@ -433,11 +437,11 @@ function itemKey(pathName: string, text: string): string {
 export function collectPromotableAddedItemLines(diffText: string): Map<string, Set<number>> {
 	const candidates: AddedItemCandidate[] = [];
 	const removals: RemovedItemOccurrence[] = [];
+	const addedReleaseHeadingHunks = new Set<string>();
 	let currentPath = "";
 	let oldLine = 0;
 	let newLine = 0;
 	let hunkIndex = -1;
-
 	for (const rawLine of diffText.replace(/\r\n/g, "\n").split("\n")) {
 		if (rawLine.startsWith("+++ b/")) {
 			currentPath = rawLine.slice("+++ b/".length);
@@ -464,6 +468,10 @@ export function collectPromotableAddedItemLines(diffText: string): Map<string, S
 		const text = rawLine.slice(1);
 		const hunk = { path: currentPath, index: hunkIndex };
 		if (marker === "+") {
+			const hunkKeyValue = hunkKey(hunk);
+			if (isAddedReleaseHeadingLine(rawLine)) {
+				addedReleaseHeadingHunks.add(hunkKeyValue);
+			}
 			if (isListItemLine(text)) {
 				candidates.push({
 					path: currentPath,
@@ -525,8 +533,8 @@ export function collectPromotableAddedItemLines(diffText: string): Map<string, S
 
 	const linesByPath = new Map<string, Set<number>>();
 	for (const candidate of candidates) {
-		if (candidate.pairedWithRemoval) continue;
 		const key = hunkKey(candidate.hunk);
+		if (candidate.pairedWithRemoval || addedReleaseHeadingHunks.has(key)) continue;
 		const unpairedRemovalCount = unpairedRemovalCountByHunk.get(key) ?? 0;
 		if (unpairedRemovalCount > 0) {
 			unpairedRemovalCountByHunk.set(key, unpairedRemovalCount - 1);