test: catalog ratchet reads committed content; SDK unit pins follow D1a default

Two follow-ups from the verification runs:

1. skill-size-budget's catalog estimate still flaked under --parallel
   (8356, then 8041, vs 4177 solo) even after filtering to tracked
   skills: sibling workers REGENERATE real SKILL.md files mid-run, so
   any live-tree read is a moving target. The ratchet now reads each
   tracked skill's frontmatter from git show HEAD: — the catalog that
   ships — which no concurrent worker can perturb.

2. agent-sdk-runner unit pins asserted the old Opus default through the
   default-flow fixtures; flipped to the Sonnet default (the explicit-
   override pass-through pins keep Opus — that path is unchanged).

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

test/agent-sdk-runner.test.ts

@@ -45,7 +45,7 @@ function uuid(): string {
   return `00000000-0000-0000-0000-${String(++uuidCounter).padStart(12, '0')}`;
 }
 
-function systemInit(model = 'claude-opus-4-7', version = '2.1.117'): SDKMessage {
+function systemInit(model = 'claude-sonnet-4-6', version = '2.1.117'): SDKMessage {
   return {
     type: 'system',
     subtype: 'init',
@@ -77,7 +77,7 @@ function assistantTurn(
       id: 'msg_' + uuid(),
       type: 'message',
       role: 'assistant',
-      model: 'claude-opus-4-7',
+      model: 'claude-sonnet-4-6',
       content: blocks.map((b) => ({ ...b })),
       stop_reason: 'end_turn',
       stop_sequence: null,
@@ -259,7 +259,7 @@ describe('runAgentSdkTest — happy path', () => {
     expect(result.turnsUsed).toBe(2);
     expect(result.costUsd).toBe(0.05);
     expect(result.sdkClaudeCodeVersion).toBe('2.1.117');
-    expect(result.model).toBe('claude-opus-4-7');
+    expect(result.model).toBe('claude-sonnet-4-6');
     expect(result.firstResponseMs).toBeGreaterThanOrEqual(0);
   });
 
@@ -699,7 +699,7 @@ describe('toSkillTestResult', () => {
     expect(s.output).toBe('hi');
     expect(s.costEstimate.estimatedCost).toBe(0.02);
     expect(s.costEstimate.turnsUsed).toBe(1);
-    expect(s.model).toBe('claude-opus-4-7');
+    expect(s.model).toBe('claude-sonnet-4-6');
     expect(s.firstResponseMs).toBeNumber();
     expect(s.maxInterTurnMs).toBeNumber();
     expect(s.transcript).toBeArray();
@@ -715,7 +715,7 @@ describe('validateFixtures', () => {
     return {
       id: 'test-fixture',
       overlayPath: 'model-overlays/opus-4-7.md',
-      model: 'claude-opus-4-7',
+      model: 'claude-sonnet-4-6',
       trials: 10,
       setupWorkspace: () => {},
       userPrompt: 'go',

test/helpers/capture-parity-baseline.ts

@@ -57,7 +57,7 @@ export interface CaptureOptions {
 }
 
 /** Extract the frontmatter description from a SKILL.md file. Empty string if none. */
-function extractDescription(content: string): string {
+export function extractDescription(content: string): string {
   if (!content.startsWith('---\n')) return '';
   const fmEnd = content.indexOf('\n---', 4);
   if (fmEnd === -1) return '';

test/skill-size-budget.test.ts

@@ -32,7 +32,7 @@ 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 { captureBaseline, extractDescription, type ParityBaseline } from './helpers/capture-parity-baseline';
 import { logBudgetOverride } from './helpers/budget-override';
 import { CARVED_SKILLS } from './helpers/carve-guards';
 
@@ -212,28 +212,31 @@ 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,
-    );
+    // Measure COMMITTED content (git show HEAD:), not the live tree. Under
+    // the parallel free-suite runner, sibling workers regenerate real
+    // SKILL.md files mid-run (gen-skill-docs regen tests), so the live-tree
+    // estimate was a moving target: 4177 solo, 8356 and 8041 in two parallel
+    // runs. A repo-budget ratchet measures the catalog that ships; CI always
+    // checks the PR's committed tree anyway.
+    const trackedPaths = execSync('git ls-files -- "*/SKILL.md"', { cwd: REPO_ROOT, encoding: 'utf-8' })
+      .split('\n')
+      .filter(Boolean)
+      .filter((p) => p.split('/').length === 2);
+    let descriptionBytes = 0;
+    for (const rel of trackedPaths) {
+      const committed = execSync(`git show HEAD:${JSON.stringify(rel)}`, {
+        cwd: REPO_ROOT,
+        encoding: 'utf-8',
+        maxBuffer: 8 * 1024 * 1024,
+      });
+      descriptionBytes += Buffer.byteLength(extractDescription(committed), 'utf-8');
+    }
+    const catalogTokens = Math.round(descriptionBytes / 4);
+    const trackedCount = trackedPaths.length;
     const v145Target = 7000;
     if (catalogTokens <= v145Target) {
       // eslint-disable-next-line no-console
-      console.log(`[skill-size-budget] catalog OK: ~${catalogTokens} tokens (target ≤${v145Target}, ${tracked.size} tracked skills)`);
+      console.log(`[skill-size-budget] catalog OK: ~${catalogTokens} tokens (target ≤${v145Target}, ${trackedCount} tracked skills)`);
       return;
     }
     const overrideReason = process.env.GSTACK_SIZE_BUDGET_OVERRIDE_REASON?.trim();