@@ -32,6 +32,23 @@ import { ALL_CONVERSIONS } from './registry.js';
  *     version from the census's last release up to the label — it landed either
  *     before the bump or after it, and only the new tarball can say which.
  *     Refreshing the census after the publish closes the tolerance again.
+ *
+ * The label is read on its RELEASE TRIPLE. Changesets pre mode writes a
+ * prerelease label (`18.0.0-next.0`) into this package on the Version Packages
+ * PR, and onto `main` once that lands, so every comparison against the label
+ * uses `x.y.z` with the prerelease suffix dropped: `18.0.0-next.N` reads as
+ * `18.0.0`. That is the reading the artifact door gives the runtime label (it
+ * compares `x.y.z` triples and tolerates a suffix), and on a stable label it is
+ * the label itself, so no assertion changes meaning there. Under a prerelease
+ * label the census never records that label's tarball (it holds stable
+ * releases only), so the release-pending tolerance above stays open, spanning
+ * `[last censused release, release triple]`, until the stable release is
+ * published and censused, when the PUBLISHED rule re-judges every stamp. Which
+ * stamp a retirement landing under a prerelease label should carry is the
+ * artifact door's window question, and this file follows that rule rather
+ * than settling it. Only the label gets this reading: a census version and a
+ * `retiredAfter` stamp stay stable `x.y.z`, and a label that is neither
+ * `x.y.z` nor `x.y.z-PRERELEASE` still throws.
  */
 
 type Triple = [number, number, number];
@@ -69,6 +86,22 @@ function cmp(a: string, b: string): number {
   return 0;
 }
 
+/**
+ * The release triple of a package label: `x.y.z` as is, `x.y.z-PRERELEASE`
+ * with the suffix dropped (`18.0.0-next.0` reads as `18.0.0`). Anything else
+ * throws. See the file docblock for why the label alone is read this way.
+ */
+function releaseTriple(label: string): string {
+  const m = /^(\d+\.\d+\.\d+)(?:-[0-9A-Za-z-]+(?:\.[0-9A-Za-z-]+)*)?$/.exec(label);
+  if (!m) throw new Error(`not an x.y.z or x.y.z-prerelease package label: '${label}'`);
+  return m[1]!;
+}
+
+/** The label as every comparison below reads it. */
+const RELEASE = releaseTriple(LABEL);
+/** The label as a failure message names it. */
+const LABEL_SHOWN = LABEL === RELEASE ? `'${LABEL}'` : `'${LABEL}' (release triple '${RELEASE}')`;
+
 const LAST_CENSUSED = CENSUS.releases.at(-1)!.version;
 
 /**
@@ -91,7 +124,7 @@ describe('retiredAfter census — every retired entry stamped from the published
     for (let i = 1; i < versions.length; i++) {
       expect(cmp(versions[i - 1]!, versions[i]!), `${versions[i - 1]} < ${versions[i]}`).toBe(-1);
     }
-    expect(cmp(LAST_CENSUSED, LABEL), `census (${LAST_CENSUSED}) is ahead of the label (${LABEL})`).toBeLessThanOrEqual(0);
+    expect(cmp(LAST_CENSUSED, RELEASE), `census (${LAST_CENSUSED}) is ahead of the label ${LABEL_SHOWN}`).toBeLessThanOrEqual(0);
     for (const r of CENSUS.releases) {
       expect(r.integrity).toMatch(/^sha512-/);
       expect([...r.retired].sort()).toEqual(r.retired);
@@ -102,7 +135,7 @@ describe('retiredAfter census — every retired entry stamped from the published
     expect(RETIRED.length).toBeGreaterThan(0);
     for (const c of RETIRED) {
       expect(c.retiredAfter, c.id).toMatch(/^\d+\.\d+\.\d+$/);
-      expect(cmp(c.retiredAfter!, LABEL), `${c.id}: retiredAfter ${c.retiredAfter} > label ${LABEL}`).toBeLessThanOrEqual(0);
+      expect(cmp(c.retiredAfter!, RELEASE), `${c.id}: retiredAfter ${c.retiredAfter} > label ${LABEL_SHOWN}`).toBeLessThanOrEqual(0);
     }
   });
 
@@ -126,17 +159,44 @@ describe('retiredAfter census — every retired entry stamped from the published
   });
 
   it('every UNPUBLISHED entry carries the package label (the release-pending range while the census trails it)', () => {
-    const pending = cmp(LABEL, LAST_CENSUSED) > 0;
+    const pending = cmp(RELEASE, LAST_CENSUSED) > 0;
     const wrong: string[] = [];
     for (const c of RETIRED) {
       if (publishedRetiredAfter(c.id) !== null) continue;
       const v = c.retiredAfter!;
-      if (!pending && v !== LABEL) {
-        wrong.push(`${c.id}: retiredAfter '${v}', but no published tarball retires it, so it takes the label '${LABEL}'`);
-      } else if (pending && (cmp(v, LAST_CENSUSED) < 0 || cmp(v, LABEL) > 0)) {
-        wrong.push(`${c.id}: retiredAfter '${v}' is outside [${LAST_CENSUSED}, ${LABEL}] — refresh the census (${REGEN})`);
+      if (!pending && v !== RELEASE) {
+        wrong.push(`${c.id}: retiredAfter '${v}', but no published tarball retires it, so it takes the label ${LABEL_SHOWN}`);
+      } else if (pending && (cmp(v, LAST_CENSUSED) < 0 || cmp(v, RELEASE) > 0)) {
+        wrong.push(`${c.id}: retiredAfter '${v}' is outside [${LAST_CENSUSED}, ${RELEASE}] — refresh the census (${REGEN})`);
       }
     }
     expect(wrong).toEqual([]);
   });
 });
+
+describe('the package label is read on its release triple', () => {
+  it('a stable label is its own release triple', () => {
+    expect(releaseTriple('17.7.0')).toBe('17.7.0');
+    expect(releaseTriple('18.0.0')).toBe('18.0.0');
+  });
+
+  it('a prerelease label reads as its release triple', () => {
+    expect(releaseTriple('18.0.0-next.0')).toBe('18.0.0');
+    expect(releaseTriple('18.0.0-next.12')).toBe('18.0.0');
+    expect(releaseTriple('18.1.0-rc.1')).toBe('18.1.0');
+    // ...and so compares at, never above, the release it precedes.
+    expect(cmp('17.7.0', releaseTriple('18.0.0-next.0'))).toBe(-1);
+    expect(cmp('18.0.0', releaseTriple('18.0.0-next.0'))).toBe(0);
+  });
+
+  it('a malformed label still throws, naming the label', () => {
+    for (const bad of ['', 'next', '18', '18.0', 'v18.0.0', '18.0.0-', '18.0.0-next..0', '18.0.0.0', ' 18.0.0']) {
+      expect(() => releaseTriple(bad), JSON.stringify(bad)).toThrow(`'${bad}'`);
+    }
+  });
+
+  it('the release-triple reading is the label\'s alone: a census version or a stamp stays stable x.y.z', () => {
+    expect(() => triple('18.0.0-next.0')).toThrow(`'18.0.0-next.0'`);
+    expect(() => cmp('18.0.0-next.0', '17.7.0')).toThrow(`'18.0.0-next.0'`);
+  });
+});