Replace absolute home directory prefix with ~ in skill <location> tags
injected into the system prompt. Models understand ~ expansion and the
read tool resolves it, so this is a safe, backward-compatible change.
Saves ~5-6 tokens per skill path. For a workspace with 90+ skills,
this reduces system prompt size by ~400-600 tokens.
Changes:
- Add compactSkillPaths() helper in workspace.ts
- Apply in buildWorkspaceSkillSnapshot and buildWorkspaceSkillsPrompt
- Add test for path compaction behavior
Before: /Users/alice/.bun/install/global/node_modules/openclaw/skills/github/SKILL.md
After: ~/.bun/install/global/node_modules/openclaw/skills/github/SKILL.md
