FN-7875: split archived pre-0.50 release notes out of root CHANGELOG.md

Adds a deterministic changelog-archive split so scripts/release.mjs stops regenerating one ever-growing root CHANGELOG.md and instead keeps only current release notes at the root while durably archiving pre-0.50.0 history.

- Add scripts/lib/changelog-archive.mjs with partitionVersionsByCutoff (splits a version-ordered list at the 0.50.0 cutoff, preserving order and treating non-parseable keys as archived) and archivePointerLine (renders the "older releases" pointer appended to the current changelog).
- Rework scripts/release.mjs's syncRootChangelog to build CHANGELOG.md (current versions + archive pointer) and a new CHANGELOG-archive.md (versions before 0.50.0) via a shared buildRootChangelogLines/normalizeChangelogLines helper instead of one monolithic file.
- Add scripts/__tests__/changelog-archive.test.mjs covering cutoff partitioning, boundary/patch handling, non-parseable keys, custom cutoffs, and the archive pointer text.
- Regenerate CHANGELOG.md (now only 0.50.0+) and add CHANGELOG-archive.md containing the pre-0.50.0 history moved out of the root file.

Files changed:
 CHANGELOG-archive.md                         | 10882 +++++++++++++++++++++++
 CHANGELOG.md                                 | 11717 ++-----------------------
 scripts/__tests__/changelog-archive.test.mjs |    58 +
 scripts/lib/changelog-archive.mjs            |    56 +
 scripts/release.mjs                          |    49 +-
 5 files changed, 11710 insertions(+), 11052 deletions(-)

Fusion-Task-Id: FN-7875
Fusion-Task-Lineage: 220e6aa1-54fb-4800-a86e-6d8d21f6bf18
Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai>

scripts/__tests__/changelog-archive.test.mjs

@@ -0,0 +1,58 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+
+import {
+  archivePointerLine,
+  CHANGELOG_ARCHIVE_CUTOFF,
+  CHANGELOG_ARCHIVE_FILE,
+  partitionVersionsByCutoff,
+} from "../lib/changelog-archive.mjs";
+
+test("partitions versions at the pre-0.50 archive cutoff", () => {
+  assert.deepEqual(
+    partitionVersionsByCutoff(["0.58.0", "0.50.0", "0.49.0", "0.11.1"]),
+    {
+      current: ["0.58.0", "0.50.0"],
+      archived: ["0.49.0", "0.11.1"],
+    },
+  );
+});
+
+test("keeps the 0.50.0 boundary and newer patch versions current", () => {
+  const partitioned = partitionVersionsByCutoff(["0.53.1", "0.50.0", "0.49.0"]);
+
+  assert.deepEqual(partitioned.current, ["0.53.1", "0.50.0"]);
+  assert.deepEqual(partitioned.archived, ["0.49.0"]);
+});
+
+test("preserves input order and archives non-parseable version keys", () => {
+  const partitioned = partitionVersionsByCutoff([
+    "0.51.0",
+    "legacy notes",
+    "0.50.0 (pre-release, unpublished)",
+    "0.49.9",
+    "0.53.0",
+  ]);
+
+  assert.deepEqual(partitioned.current, [
+    "0.51.0",
+    "0.50.0 (pre-release, unpublished)",
+    "0.53.0",
+  ]);
+  assert.deepEqual(partitioned.archived, ["legacy notes", "0.49.9"]);
+});
+
+test("supports a custom cutoff with release.mjs semver-ish parsing", () => {
+  assert.deepEqual(partitionVersionsByCutoff(["1.2.0", "1.1.9", "not semver"], "1.2.0"), {
+    current: ["1.2.0"],
+    archived: ["1.1.9", "not semver"],
+  });
+});
+
+test("archive pointer references the archive file and cutoff", () => {
+  const pointer = archivePointerLine();
+
+  assert.ok(pointer.includes(CHANGELOG_ARCHIVE_FILE));
+  assert.ok(pointer.includes(CHANGELOG_ARCHIVE_CUTOFF));
+  assert.match(pointer, /\.\/CHANGELOG-archive\.md/);
+});

scripts/lib/changelog-archive.mjs

@@ -0,0 +1,56 @@
+/**
+ * FNXC:ReleaseChangelog 2026-07-12-00:00:
+ * The root CHANGELOG.md is regenerated by scripts/release.mjs on every release, so pruning old release notes by hand would be reverted.
+ * Keep the 0.50.0 cutoff in generator-owned pure logic so current release notes stay in CHANGELOG.md and older notes are durably split into CHANGELOG-archive.md.
+ */
+export const CHANGELOG_ARCHIVE_CUTOFF = "0.50.0";
+export const CHANGELOG_ARCHIVE_FILE = "CHANGELOG-archive.md";
+
+/**
+ * Partition version keys while preserving the source changelog order inside each bucket.
+ * Versions greater than or equal to the cutoff remain in the current changelog; versions below it, including non-parseable keys treated as 0.0.0, move to the archive.
+ *
+ * @param {string[]} versionOrder
+ * @param {string} cutoff
+ * @returns {{ current: string[], archived: string[] }}
+ */
+export function partitionVersionsByCutoff(versionOrder, cutoff = CHANGELOG_ARCHIVE_CUTOFF) {
+  const current = [];
+  const archived = [];
+
+  for (const version of versionOrder) {
+    if (compareSemver(version, cutoff) >= 0) {
+      current.push(version);
+    } else {
+      archived.push(version);
+    }
+  }
+
+  return { current, archived };
+}
+
+/**
+ * Return the stable archive pointer appended to the current root changelog.
+ *
+ * @param {string} archiveFile
+ * @returns {string}
+ */
+export function archivePointerLine(archiveFile = CHANGELOG_ARCHIVE_FILE) {
+  return `> Older releases (before ${CHANGELOG_ARCHIVE_CUTOFF}) are archived in [\`${archiveFile}\`](./${archiveFile}).`;
+}
+
+/** Compare two semver-ish version strings ("0.2.5", "0.4.0 (pre-release)"). */
+function compareSemver(a, b) {
+  const pa = parseVersionKey(a);
+  const pb = parseVersionKey(b);
+  for (let i = 0; i < 3; i++) {
+    if (pa[i] !== pb[i]) return pa[i] - pb[i];
+  }
+  return 0;
+}
+
+function parseVersionKey(key) {
+  const m = key.match(/^(\d+)\.(\d+)\.(\d+)/);
+  if (!m) return [0, 0, 0];
+  return [Number(m[1]), Number(m[2]), Number(m[3])];
+}

scripts/release.mjs

@@ -37,6 +37,12 @@ import { extractVersionNotes, replaceVersionSection } from "./lib/extract-versio
 import { parseChangesetFile } from "./lib/changeset-schema.mjs";
 import { distillDeterministic } from "./lib/distill-release-notes.mjs";
 import { shouldPromptForVersion } from "./lib/release-prompt-gate.mjs";
+import {
+  archivePointerLine,
+  CHANGELOG_ARCHIVE_CUTOFF,
+  CHANGELOG_ARCHIVE_FILE,
+  partitionVersionsByCutoff,
+} from "./lib/changelog-archive.mjs";
 
 const args = new Set(process.argv.slice(2));
 /*
@@ -68,7 +74,7 @@ function run(cmd, { capture = false, allowFail = false, cwd } = {}) {
 }
 
 /**
- * Rewrite the repo-root CHANGELOG.md by aggregating every
+ * Rewrite the repo-root changelogs by aggregating every
  * `packages/*\/CHANGELOG.md` into a single per-version view.
  *
  * For each version that appears in any package, we emit a top-level
@@ -80,6 +86,10 @@ function run(cmd, { capture = false, allowFail = false, cwd } = {}) {
  * release (the one whose top version is highest by semver). Any extra
  * versions found only in other packages are appended in semver-descending
  * order at the end.
+ *
+ * FNXC:ReleaseChangelog 2026-07-12-00:00:
+ * The root CHANGELOG.md is regenerated during every release, so the pre-0.50 prune must happen in this generator instead of as a manual docs edit.
+ * Keep versions greater than or equal to the 0.50.0 cutoff in CHANGELOG.md, and write older versions to CHANGELOG-archive.md so the split survives the next release sync.
  */
 function syncRootChangelog() {
   const pkgsDir = "packages";
@@ -113,12 +123,31 @@ function syncRootChangelog() {
     }
   }
 
-  const lines = [
-    "# Fusion changelog",
-    "",
-    "User-facing release notes aggregated across all packages. This file is auto-synced from each `packages/*/CHANGELOG.md` by `scripts/release.mjs` — do not edit by hand.",
-    "",
-  ];
+  const { current, archived } = partitionVersionsByCutoff(versionOrder);
+  const currentLines = buildRootChangelogLines({
+    title: "# Fusion changelog",
+    banner: "User-facing release notes aggregated across all packages. This file is auto-synced from each `packages/*/CHANGELOG.md` by `scripts/release.mjs` — do not edit by hand.",
+    parsed,
+    versionOrder: current,
+  });
+
+  if (archived.length > 0) {
+    currentLines.push(archivePointerLine(), "");
+  }
+
+  const archiveLines = buildRootChangelogLines({
+    title: "# Fusion changelog archive",
+    banner: `Archived release notes before ${CHANGELOG_ARCHIVE_CUTOFF}. This file is auto-synced from each \`packages/*/CHANGELOG.md\` by \`scripts/release.mjs\` — do not edit by hand.`,
+    parsed,
+    versionOrder: archived,
+  });
+
+  writeFileSync("CHANGELOG.md", normalizeChangelogLines(currentLines));
+  writeFileSync(CHANGELOG_ARCHIVE_FILE, normalizeChangelogLines(archiveLines));
+}
+
+function buildRootChangelogLines({ title, banner, parsed, versionOrder }) {
+  const lines = [title, "", banner, ""];
 
   for (const version of versionOrder) {
     lines.push(`## ${version}`, "");
@@ -136,7 +165,11 @@ function syncRootChangelog() {
     }
   }
 
-  writeFileSync("CHANGELOG.md", lines.join("\n").replace(/\n{3,}/g, "\n\n"));
+  return lines;
+}
+
+function normalizeChangelogLines(lines) {
+  return lines.join("\n").replace(/\n{3,}/g, "\n\n");
 }
 
 /**