test: fix two parallelism-exposed flakes (probe re-run, live-tree census)

Both pass solo and on main but flaked under the parallel runner:

1. gstack-brain-context-load probed 'gbrain --version' PER QUERY with a
   500ms budget — a cold probe on a saturated box timed out (observed
   505ms), branding gbrain 'missing' for one query while siblings
   passed. The probe is now memoized (availability can't change
   mid-invocation) with a generous one-time 5s budget; query calls keep
   the tight timeout.

2. skill-size-budget's catalog estimate read the LIVE tree, so a
   concurrent worker's transient skill-shaped scratch dirs exactly
   doubled it (8356 vs 4177). The ratchet now counts git-TRACKED skills
   only — the catalog that ships, immune to sibling workers.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

bin/gstack-brain-context-load.ts

@@ -190,16 +190,26 @@ function resolveSkillFile(args: CliArgs): string | null {
 
 // ── Dispatchers ────────────────────────────────────────────────────────────
 
+// Memoized: availability can't change mid-invocation, and the per-query
+// re-probe was both wasteful (N probes per run) and load-flaky — a cold
+// `gbrain --version` on a saturated box can exceed the 500ms budget, branding
+// gbrain "missing" for one query while its siblings succeed (observed under
+// the parallel free-suite runner: SKIP at dur=505ms with two OKs after it).
+let _gbrainAvailable: boolean | null = null;
 function gbrainAvailable(): boolean {
+  if (_gbrainAvailable !== null) return _gbrainAvailable;
   try {
     execFileSync("gbrain", ["--version"], {
       stdio: "ignore",
-      timeout: MCP_TIMEOUT_MS,
+      // Generous first-probe budget: this runs ONCE, and a slow-to-start CLI
+      // is not a missing CLI. Query calls keep the tight MCP_TIMEOUT_MS.
+      timeout: 5_000,
     });
-    return true;
+    _gbrainAvailable = true;
   } catch {
-    return false;
+    _gbrainAvailable = false;
   }
+  return _gbrainAvailable;
 }
 
 function dispatchVector(q: GbrainManifestQuery, args: CliArgs): QueryResult {

test/skill-size-budget.test.ts

@@ -31,6 +31,7 @@
 import { describe, test, expect } from 'bun:test';
 import * as fs from 'fs';
 import * as path from 'path';
+import { execSync } from 'child_process';
 import { captureBaseline, type ParityBaseline } from './helpers/capture-parity-baseline';
 import { logBudgetOverride } from './helpers/budget-override';
 import { CARVED_SKILLS } from './helpers/carve-guards';
@@ -212,10 +213,27 @@ describe('SKILL.md size budget regression (gate, free)', () => {
 
   test('catalog token estimate stays compressed (v1.45 target ≤ 7000)', () => {
     const current = captureBaseline({ repoRoot: REPO_ROOT });
+    // Count only git-TRACKED skills. Under the parallel free-suite runner,
+    // concurrent test files can leave transient skill-shaped dirs in the live
+    // repo mid-run (observed: this estimate exactly DOUBLED, 8356 vs 4177,
+    // while a solo run passed). A repo-budget ratchet should measure the
+    // catalog that ships, not another worker's scratch state.
+    const tracked = new Set(
+      execSync('git ls-files -- "*/SKILL.md"', { cwd: REPO_ROOT, encoding: 'utf-8' })
+        .split('\n')
+        .filter(Boolean)
+        .filter((p) => p.split('/').length === 2)
+        .map((p) => p.split('/')[0]),
+    );
+    const catalogTokens = Math.round(
+      Object.values(current.skills)
+        .filter((s) => tracked.has(s.skill))
+        .reduce((sum, s) => sum + s.descriptionLen, 0) / 4,
+    );
     const v145Target = 7000;
-    if (current.estTotalCatalogTokens <= v145Target) {
+    if (catalogTokens <= v145Target) {
       // eslint-disable-next-line no-console
-      console.log(`[skill-size-budget] catalog OK: ~${current.estTotalCatalogTokens} tokens (target ≤${v145Target})`);
+      console.log(`[skill-size-budget] catalog OK: ~${catalogTokens} tokens (target ≤${v145Target}, ${tracked.size} tracked skills)`);
       return;
     }
     const overrideReason = process.env.GSTACK_SIZE_BUDGET_OVERRIDE_REASON?.trim();
@@ -223,12 +241,12 @@ describe('SKILL.md size budget regression (gate, free)', () => {
       logBudgetOverride({
         scope: 'skill-size-budget-catalog',
         reason: overrideReason,
-        details: { target: v145Target, observed: current.estTotalCatalogTokens },
+        details: { target: v145Target, observed: catalogTokens },
       });
       return;
     }
     throw new Error(
-      `Catalog token estimate regressed past v1.45 target: ${current.estTotalCatalogTokens} tokens > ${v145Target}. ` +
+      `Catalog token estimate regressed past v1.45 target: ${catalogTokens} tokens > ${v145Target}. ` +
       `T4 catalog trim should keep this under control. Override: set GSTACK_SIZE_BUDGET_OVERRIDE_REASON to allow.`,
     );
   });