M127 Bundle A1 — cost-hygiene explorer (PR #1568)

Two changes that reduce token + API spend without changing behavior. Drag the sliders to estimate cost savings against your typical CI volume and session count.

Your usage estimate

40
4
20
15

A7: CI fork-subagent — cached prefix sharing

$0
~60% reduction on agent-heavy CI runs
CC 2.1.121 fork-subagent in SDK/print mode

S5: slash-only — description tokens reclaimed

$0
~1KB description / session × N sessions
brainstorm + implement removed from auto-routing list

What this PR changes (5 files, +9 lines)

A7
Add CLAUDE_CODE_FORK_SUBAGENT: '1' to ultrareview review step env
.github/workflows/ultrareview.yml
+5
S5
Add disable-model-invocation: true to brainstorm frontmatter
src/skills/brainstorm/SKILL.md · plugins/ork/skills/brainstorm/SKILL.md
+2
S5
Add disable-model-invocation: true to implement frontmatter
src/skills/implement/SKILL.md · plugins/ork/skills/implement/SKILL.md
+2

Bundle A roadmap

✅ A1 — this PR (#1568) · A7 + S5 config changes
⬜ A2 — H6 ENABLE_PROMPT_CACHING_1H SessionStart hook (~130 LOC + test)
⬜ A3 — S1 description budget audit (15 skills > 250 chars)