fix(release): let alpha tags publish from their exact changelog heading

Shipped alpha tags carry a dedicated ## X-alpha.N heading with no base
section (see v2026.6.20-alpha.1's tagged CHANGELOG.md); the renderer and
candidate provenance now prefer that dedicated heading for alpha and
correction tags while beta/stable remain pinned to the stable base
section per #103222.

scripts/release-candidate-checklist.mjs

@@ -8,7 +8,7 @@ import { fileURLToPath } from "node:url";
 import { stripLeadingPackageManagerSeparator } from "./lib/arg-utils.mjs";
 import { readBoundedResponseText } from "./lib/bounded-response.mjs";
 import {
-  correctionVersionForTag,
+  dedicatedSectionVersionForTag,
   extractChangelogReleaseSections,
   extractChangelogSection,
   formatShippedBaselineExclusions,
@@ -489,18 +489,19 @@ export function validateCandidateChangelogProvenance({
   isAncestor = gitIsAncestor,
   loadShippedBaseline = loadCandidateShippedBaseline,
 }) {
-  // Validate the same section the renderer publishes: correction tags may
-  // carry their own heading, and alpha tags may fall back to Unreleased.
+  // Validate the same section the renderer publishes: alpha and correction
+  // tags may carry their own heading, and alpha tags may fall back to
+  // Unreleased.
   let section;
   let sectionVersion = version;
   let usesAlphaUnreleasedFallback = false;
-  const correctionVersion = correctionVersionForTag(tag);
-  if (correctionVersion && correctionVersion !== version) {
+  const dedicatedVersion = dedicatedSectionVersionForTag(tag);
+  if (dedicatedVersion && dedicatedVersion !== version) {
     try {
-      section = extractChangelogSection(changelog, correctionVersion);
-      sectionVersion = correctionVersion;
+      section = extractChangelogSection(changelog, dedicatedVersion);
+      sectionVersion = dedicatedVersion;
     } catch {
-      // The correction has no dedicated section; validate the base section.
+      // No dedicated section; validate the base section.
     }
   }
   if (section === undefined) {

scripts/render-github-release-notes.mjs

@@ -230,24 +230,25 @@ function compactReleaseNotes(section, repository, tag) {
   ].join("\n");
 }
 
-export function correctionVersionForTag(tag) {
-  // Numeric-correction tags (vX-N) may carry their own changelog heading;
-  // alpha/beta prerelease tags never do.
+export function dedicatedSectionVersionForTag(tag) {
+  // Correction (vX-N) and alpha tags may carry their own exact changelog
+  // heading; beta and stable bodies must come from the stable base section.
   const taggedVersion = tag.replace(/^v/u, "");
-  const isCorrection =
-    /-[1-9][0-9]*$/u.test(taggedVersion) && !/-(?:alpha|beta)\.[1-9][0-9]*$/u.test(taggedVersion);
-  return isCorrection ? taggedVersion : undefined;
+  if (/-beta\.[1-9][0-9]*$/u.test(taggedVersion)) {
+    return undefined;
+  }
+  return /-(?:alpha\.)?[1-9][0-9]*$/u.test(taggedVersion) ? taggedVersion : undefined;
 }
 
 export function releaseNotesSectionForTag(changelog, version, tag) {
-  // Correction tags prefer their own exact heading when the changelog carries
-  // one; otherwise they fall back to the base version.
-  const correctionVersion = correctionVersionForTag(tag);
-  if (correctionVersion && correctionVersion !== version) {
+  // Alpha and correction tags prefer their own exact heading when the
+  // changelog carries one; otherwise they fall back to the base version.
+  const dedicatedVersion = dedicatedSectionVersionForTag(tag);
+  if (dedicatedVersion && dedicatedVersion !== version) {
     try {
-      return extractChangelogSection(changelog, correctionVersion);
+      return extractChangelogSection(changelog, dedicatedVersion);
     } catch {
-      // The correction has no dedicated section; use the base version below.
+      // No dedicated section; use the base version below.
     }
   }
   try {

test/scripts/render-github-release-notes.test.ts

@@ -239,6 +239,33 @@ describe("GitHub release-note rendering", () => {
     ).toThrow("cannot be compacted without a complete contribution record");
   });
 
+  it("prefers an alpha tag's exact changelog heading over the Unreleased fallback", () => {
+    // Shipped alpha tags carry their own heading with no base section,
+    // matching the tagged CHANGELOG.md shape of v2026.6.20-alpha.1.
+    const changelog = [
+      "# Changelog",
+      "",
+      "## 2026.7.1-alpha.2",
+      "",
+      "- Alpha-only fix.",
+      "",
+      "## 2026.6.11",
+      "",
+      "- Previous release.",
+      "",
+    ].join("\n");
+    const rendered = renderGithubReleaseNotes({
+      changelog,
+      version,
+      tag: "v2026.7.1-alpha.2",
+      repository,
+    });
+
+    expect(rendered.body).toContain("## 2026.7.1-alpha.2");
+    expect(rendered.body).toContain("Alpha-only fix.");
+    expect(rendered.body).not.toContain("Previous release.");
+  });
+
   it("permits the Unreleased fallback only for alpha tags", () => {
     const changelog = changelogFor("- **PR #123** fix: example.").replace(
       "## 2026.7.1",