diff --git a/packages/spec/scripts/dropped-refinements.test.ts b/packages/spec/scripts/dropped-refinements.test.ts
index 5dd5b6d8488..18c6a5c9a8d 100644
--- a/packages/spec/scripts/dropped-refinements.test.ts
+++ b/packages/spec/scripts/dropped-refinements.test.ts
@@ -32,6 +32,7 @@
  */
 import { describe, expect, it } from 'vitest';
 import fs from 'fs';
+import os from 'os';
 import path from 'path';
 import { z } from 'zod';
 import {
@@ -292,6 +293,60 @@ describe('the ratchet adjudicates against the ledger', () => {
   });
 });
 
+describe("the reader's refusal names the shape the reader ACCEPTS", () => {
+  // The trap (#18747): the shape diagnostic used to say the entries are
+  // `key -> { count, reason }` while the very next check in the same function
+  // requires `sites: string[]` and the shipped `DroppedRefinementsEntry` has no
+  // `count` and no `reason` at all. An author — or an AI — repairing a broken
+  // ledger by following that sentence writes a ledger the SAME function refuses
+  // again. So the pin is a closed loop, not a wording match: whatever the
+  // refusal names has to be what the reader then takes.
+  const withLedger = <T,>(json: string, fn: (pkgDir: string) => T): T => {
+    const dir = fs.mkdtempSync(path.join(os.tmpdir(), 'os-dropped-refinements-'));
+    try {
+      fs.writeFileSync(path.join(dir, DROPPED_REFINEMENTS_BASELINE_FILE), json, 'utf8');
+      return fn(dir);
+    } finally {
+      fs.rmSync(dir, { recursive: true, force: true });
+    }
+  };
+
+  const refusalFor = (json: string): string =>
+    withLedger(json, (dir) => {
+      try {
+        readDroppedRefinementsBaseline(dir);
+      } catch (error) {
+        return (error as Error).message;
+      }
+      throw new Error('the reader accepted a ledger it should have refused');
+    });
+
+  it('the shape diagnostic names `sites`', () => {
+    // `entries` as an array is the branch that prints the shape.
+    expect(refusalFor('{ "entries": [] }')).toContain('sites');
+  });
+
+  it('a ledger written to that shape is then ACCEPTED — the loop closes', () => {
+    const accepted = withLedger('{ "entries": { "a/One": { "sites": ["x"] } } }', (dir) =>
+      readDroppedRefinementsBaseline(dir),
+    );
+    expect(accepted?.entries['a/One'].sites).toEqual(['x']);
+  });
+
+  it('LIT CONTROL — the shape the OLD diagnostic named is refused, and the refusal still says `sites`', () => {
+    // Without this leg the two assertions above pass on a reader that accepts
+    // anything: this is the ledger an author following the old sentence wrote.
+    const message = refusalFor('{ "entries": { "a/One": { "count": 1, "reason": "zod drops custom checks" } } }');
+    expect(message).toContain('sites');
+  });
+
+  it('the shape diagnostic names no key the entry shape does not have', () => {
+    const message = refusalFor('{ "entries": [] }');
+    expect(message).not.toContain('count');
+    expect(message).not.toContain('reason');
+  });
+});
+
 describe('the committed ledger', () => {
   it('names at least one site per entry, and its header totals match its body', () => {
     const baseline = readDroppedRefinementsBaseline(PKG_DIR);
diff --git a/packages/spec/scripts/lib/dropped-refinements.ts b/packages/spec/scripts/lib/dropped-refinements.ts
index 84599123730..9615f4e0c02 100644
--- a/packages/spec/scripts/lib/dropped-refinements.ts
+++ b/packages/spec/scripts/lib/dropped-refinements.ts
@@ -56,18 +56,23 @@
  *
  *   - a published schema with dropped refinements that is NOT recorded fails
  *     the build — a new gap has to be a reviewed line in a diff;
- *   - a recorded `count` the build does not observe ALSO fails, in either
- *     direction. A ledger that keeps saying 3 while the tree grew to 4 has
- *     stopped describing the tree, and the 4th arrives inside a number nobody
- *     re-read.
+ *   - a recorded `sites` list the build does not observe ALSO fails, in either
+ *     direction and path by path. A ledger that keeps naming a site the tree no
+ *     longer has stopped describing the tree, and the next gap arrives inside a
+ *     list nobody re-read.
  *
  * ## Why the ledger is HAND-EDITED and has no `gen:` script
  *
  * Identical to `unemitted-schemas.baseline.json`: a generator would let a new
- * gap be admitted by running a command instead of by a decision. Every entry
- * carries a `reason` in prose and the gate requires it to be non-empty, because
- * a baseline that records only a COUNT lets the next gap slip in behind a
- * repaired one with nobody able to see which was replaced.
+ * gap be admitted by running a command instead of by a decision. Where THAT
+ * ledger requires a non-empty per-entry `reason`, this one requires a non-empty
+ * `sites` list and has no `reason` field at all — the reason is the same for
+ * every site here and is written once, above and in the ledger's own
+ * `description`, so a per-entry copy would be exactly the prose a required
+ * `reason` exists to prevent (`DroppedRefinementsEntry` below argues that in
+ * full). Both refuse the same thing: an entry recording only MEMBERSHIP, which
+ * lets the next gap slip in behind a repaired one with nobody able to see which
+ * was replaced.
  */
 import fs from 'fs';
 import path from 'path';
@@ -493,7 +498,7 @@ export function readDroppedRefinementsBaseline(pkgDir: string): DroppedRefinemen
   const parsed = JSON.parse(fs.readFileSync(file, 'utf8')) as { entries?: unknown };
   const entries = parsed.entries;
   if (typeof entries !== 'object' || entries === null || Array.isArray(entries)) {
-    throw new Error(`${DROPPED_REFINEMENTS_BASELINE_FILE}: "entries" must be an object of key -> { count, reason }`);
+    throw new Error(`${DROPPED_REFINEMENTS_BASELINE_FILE}: "entries" must be an object of key -> { sites: string[] }`);
   }
   for (const [key, value] of Object.entries(entries as Record<string, unknown>)) {
     const entry = value as Partial<DroppedRefinementsEntry>;