diff --git a/test/catalog-budget.test.ts b/test/catalog-budget.test.ts
new file mode 100644
index 000000000..b2ad347b5
--- /dev/null
+++ b/test/catalog-budget.test.ts
@@ -0,0 +1,122 @@
+import { describe, expect, test } from 'bun:test';
+import { readFileSync } from 'node:fs';
+import { join } from 'node:path';
+import { skillCensus } from './helpers/skill-census';
+
+/**
+ * Aggregate discovery-surface budget: the sum of every skill's frontmatter
+ * `name` + `description` is what EVERY host loads at discovery, every session.
+ *
+ * This is the missing enforcement layer over the existing catalog-trim
+ * mechanism: `applyCatalogTrim` in scripts/gen-skill-docs.ts (~line 865)
+ * shapes each description, and the 160KB per-file warn (~line 1015) covers
+ * BODY size — neither caps the aggregate frontmatter the catalog is made of.
+ *
+ * Import-free by design: parses skills' SKILL.md frontmatter directly. Do not
+ * import gen-skill-docs internals here — this test must survive generator
+ * refactors.
+ *
+ * Budget derivation (re-derive it, do not trust the number):
+ *   ref     this commit
+ *   method  for each authored skill (test/helpers/skill-census.ts
+ *           authoredSkills — symlink-deduped, root router excluded) plus the
+ *           root router's `_gstack-command` alias frontmatter as one separate
+ *           line item, run parseFrontmatter() below and sum
+ *           Buffer.byteLength(name) + Buffer.byteLength(description);
+ *           token-equivalents = ceil(bytes / 4).
+ *   result  53 authored skills = 4,371 bytes (1,093 token-equivalents);
+ *           + root router alias 49 bytes = 4,420 bytes total
+ *           = 1,105 token-equivalents (measured 2026-08-12)
+ * Ceiling is 1,150 token-equivalents (4,600 bytes), so headroom is 180 bytes
+ * (~4%). Dominant skill: design-consultation at 229 bytes name+description.
+ */
+const CATALOG_BUDGET_TOKEN_EQUIVALENTS = 1_150;
+
+// Largest today: design-consultation at 229 bytes. A description that needs
+// more than 260 bytes is a body paragraph, not a catalog entry.
+const PER_SKILL_BYTE_CAP = 260;
+
+const RATCHET_PROTOCOL =
+  'Adding a skill? Re-measure with: bun test test/catalog-budget.test.ts ' +
+  '(the failure prints the new total). Update CATALOG_BUDGET_TOKEN_EQUIVALENTS ' +
+  'AND the derivation comment (ref/date/value/which skill moved it) in the ' +
+  'SAME commit. Growing an existing description? Trim it instead — the ' +
+  'catalog is what every host loads at discovery, every session.';
+
+const ROOT = join(import.meta.dir, '..');
+
+function parseFrontmatter(body: string): { name: string; description: string } {
+  const name = body.match(/^name:\s*(.+)$/m)?.[1]?.trim() ?? '';
+  // Folded block scalar (description: >-) with two-space-indented continuation
+  // lines, falling back to a single-line description.
+  const folded = body.match(/^description:\s*>-?\r?\n((?:  .*\r?\n)+)/m)?.[1];
+  const description = folded
+    ? folded.split(/\r?\n/).map((line) => line.trim()).filter(Boolean).join(' ')
+    : body.match(/^description:\s*(?!>-?\s*$)(.+)$/m)?.[1]?.trim() ?? '';
+  return { name, description };
+}
+
+interface CatalogEntry {
+  skill: string;
+  name: string;
+  description: string;
+  bytes: number;
+}
+
+function catalogEntries(): CatalogEntry[] {
+  const entries: CatalogEntry[] = [];
+  for (const skill of skillCensus(ROOT).authoredSkills) {
+    const body = readFileSync(join(ROOT, skill, 'SKILL.md'), 'utf8');
+    const { name, description } = parseFrontmatter(body);
+    entries.push({
+      skill,
+      name,
+      description,
+      bytes: Buffer.byteLength(name) + Buffer.byteLength(description),
+    });
+  }
+  // The root SKILL.md is a router, registered by setup as the
+  // `_gstack-command` alias — not an authored skill, but its frontmatter
+  // still ships in the catalog, so it counts as one line item.
+  const router = parseFrontmatter(readFileSync(join(ROOT, 'SKILL.md'), 'utf8'));
+  if (router.name && router.description) {
+    entries.push({
+      skill: '(root router)',
+      name: router.name,
+      description: router.description,
+      bytes: Buffer.byteLength(router.name) + Buffer.byteLength(router.description),
+    });
+  }
+  return entries;
+}
+
+describe('catalog discovery-surface budget', () => {
+  test(`aggregate frontmatter stays within ${CATALOG_BUDGET_TOKEN_EQUIVALENTS} token-equivalents`, () => {
+    const entries = catalogEntries();
+    const totalBytes = entries.reduce((sum, e) => sum + e.bytes, 0);
+    const estimatedTokens = Math.ceil(totalBytes / 4);
+    const delta = estimatedTokens - CATALOG_BUDGET_TOKEN_EQUIVALENTS;
+    expect(
+      estimatedTokens,
+      `Catalog is ${estimatedTokens} token-equivalents (${totalBytes} bytes), ` +
+        `${delta} over the ${CATALOG_BUDGET_TOKEN_EQUIVALENTS} budget. ${RATCHET_PROTOCOL}`
+    ).toBeLessThanOrEqual(CATALOG_BUDGET_TOKEN_EQUIVALENTS);
+  });
+
+  test(`every skill's name + description stays under ${PER_SKILL_BYTE_CAP} bytes`, () => {
+    for (const entry of catalogEntries()) {
+      expect(
+        entry.bytes,
+        `${entry.skill}: name + description is ${entry.bytes} bytes, ` +
+          `${entry.bytes - PER_SKILL_BYTE_CAP} over the ${PER_SKILL_BYTE_CAP}-byte ` +
+          `per-skill cap. ${RATCHET_PROTOCOL}`
+      ).toBeLessThanOrEqual(PER_SKILL_BYTE_CAP);
+    }
+  });
+
+  test('every skill has a non-empty description', () => {
+    for (const entry of catalogEntries()) {
+      expect(entry.description, `${entry.skill}: empty or missing frontmatter description`).not.toBe('');
+    }
+  });
+});