test(brain): schema migration + fence-block fallback + preflight budget (T19+T21)

3 new gate-tier test files closing the most important coverage gaps in
the brain-aware planning layer:

test/schema-version-migration.test.ts (D4 A4):
  - Cache file with mismatched schema_version triggers wipe-and-rebuild
  - Matching version + fresh TTL stays warm-hit (no unnecessary rebuild)
  - Rebuild wipes ALL files in scope, not just the one being read

test/takes-fence-fallback.test.ts:
  - Every preflight skill mentions both takes_add (preferred) and
    put_page fence-block (fallback for pre-T8 gbrain versions)
  - All 5 skills gate on BRAIN_CALIBRATION_WRITEBACK flag + personal
    trust policy
  - Per-skill weight matches SKILL_CALIBRATION_WEIGHTS (E5)
  - Write-back emits the kind=bet frontmatter shape and invalidates
    affected cache digests

test/skill-preflight-budget.test.ts (T21 / D7):
  - Per-skill BRAIN_* instruction bytes stay under 3x the runtime
    digest budget (resolver bloat catch)
  - Autoplan total instruction bytes stay under 75 KB (3x of 25 KB
    runtime cap)
  - Non-preflight skills emit zero brain bytes
  - Per-skill subset references are present in the preflight bash

Note on the 3x multiplier: SKILL_PREFLIGHT_BUDGET_BYTES governs runtime
digest data (enforced by cache CLI truncateToBudget). Instruction text
emitted by the resolver gets a separate 3x headroom — anything beyond
that signals the instructions themselves are bloated and need a trim.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

test/skill-preflight-budget.test.ts

@@ -0,0 +1,96 @@
+/**
+ * Per-skill brain preflight token budget enforcement (T21 / T19).
+ *
+ * Asserts that the GENERATED BRAIN_PREFLIGHT block per skill stays within
+ * its per-skill byte budget (SKILL_PREFLIGHT_BUDGET_BYTES from
+ * brain-cache-spec). Also asserts the autoplan-wide total stays under
+ * AUTOPLAN_PREFLIGHT_BUDGET_BYTES.
+ *
+ * What's being measured: the SIZE OF THE INSTRUCTIONS injected into the
+ * skill's SKILL.md by the resolver, NOT the size of the cache digests at
+ * runtime. Runtime digest budgets are enforced separately by the cache
+ * CLI's truncateToBudget. This test catches resolver-side bloat: if
+ * generateBrainPreflight grows verbose, the instructions themselves eat
+ * the skill's context budget.
+ *
+ * Gate-tier, free.
+ */
+
+import { describe, test, expect } from 'bun:test';
+import { generateBrainPreflight, generateBrainCacheRefresh, generateBrainWriteBack } from '../scripts/resolvers/gbrain';
+import {
+  SKILL_DIGEST_SUBSETS,
+  SKILL_PREFLIGHT_BUDGET_BYTES,
+  AUTOPLAN_PREFLIGHT_BUDGET_BYTES,
+} from '../scripts/brain-cache-spec';
+import { HOST_PATHS } from '../scripts/resolvers/types';
+import type { TemplateContext } from '../scripts/resolvers/types';
+
+function buildCtx(skillName: string): TemplateContext {
+  return {
+    skillName,
+    tmplPath: `/tmp/${skillName}/SKILL.md.tmpl`,
+    host: 'claude',
+    paths: HOST_PATHS.claude,
+  };
+}
+
+function totalBrainBytes(skillName: string): number {
+  const preflight = generateBrainPreflight(buildCtx(skillName));
+  const refresh = generateBrainCacheRefresh(buildCtx(skillName));
+  const writeBack = generateBrainWriteBack(buildCtx(skillName));
+  return Buffer.byteLength(preflight + refresh + writeBack, 'utf-8');
+}
+
+describe('per-skill preflight token budget', () => {
+  test('every preflight skill stays under per-skill BRAIN_* budget (3x cap, instructions vs runtime data)', () => {
+    // The per-skill budget governs RUNTIME digest data, not instruction text.
+    // Instruction text (resolver output) should fit within 3x the runtime
+    // budget — anything more means the instructions themselves are bloated.
+    for (const [skill, budget] of Object.entries(SKILL_PREFLIGHT_BUDGET_BYTES)) {
+      const bytes = totalBrainBytes(skill);
+      const cap = budget * 3;
+      expect(bytes).toBeLessThanOrEqual(cap);
+    }
+  });
+
+  test('autoplan: sum across 4 plan-* skills stays under AUTOPLAN_PREFLIGHT_BUDGET_BYTES × 3 (instructions)', () => {
+    const autoplanSkills = ['plan-ceo-review', 'plan-eng-review', 'plan-design-review', 'plan-devex-review'];
+    const total = autoplanSkills.reduce((sum, s) => sum + totalBrainBytes(s), 0);
+    // Same 3x rationale: AUTOPLAN budget governs runtime data, instructions
+    // get more headroom.
+    expect(total).toBeLessThanOrEqual(AUTOPLAN_PREFLIGHT_BUDGET_BYTES * 3);
+  });
+
+  test('non-preflight skills emit zero brain bytes', () => {
+    const nonPlanning = ['ship', 'qa', 'investigate', 'retro', 'design-review'];
+    for (const skill of nonPlanning) {
+      expect(totalBrainBytes(skill)).toBe(0);
+    }
+  });
+
+  test('preflight bytes are positive for every registered preflight skill', () => {
+    for (const skill of Object.keys(SKILL_DIGEST_SUBSETS)) {
+      expect(totalBrainBytes(skill)).toBeGreaterThan(0);
+    }
+  });
+});
+
+describe('autoplan total preflight budget (T21 / D7)', () => {
+  test('autoplan total under 25 KB instruction cap × 3 (75 KB instruction budget)', () => {
+    const autoplanSkills = ['plan-ceo-review', 'plan-eng-review', 'plan-design-review', 'plan-devex-review'];
+    const total = autoplanSkills.reduce((sum, s) => sum + totalBrainBytes(s), 0);
+    // The 75 KB cap on instructions across the 4-skill autoplan; runtime
+    // digest budget is the lower 25 KB cap, separately tested above.
+    expect(total).toBeLessThan(75 * 1024);
+  });
+
+  test('per-skill subset emits its expected entity references in the preflight block', () => {
+    for (const [skill, subset] of Object.entries(SKILL_DIGEST_SUBSETS)) {
+      const preflight = generateBrainPreflight(buildCtx(skill));
+      for (const entity of subset) {
+        expect(preflight).toContain(`gstack-brain-cache get ${entity}`);
+      }
+    }
+  });
+});