#733 fix(skills): install all default sandbox skills (build-os ref + resilient install)

Part of recoupable/chat#1833 (prerequisite item). Base: main.

Problem

Task sandboxes shipped with only 2 of 6 default skills. Two bugs:

1. DEFAULT_GLOBAL_SKILL_REFS listed recoup-platform-build-workspace (renamed to recoup-platform-build-os) → npx skills add 404s.
2. installGlobalSkills threw on the first failure, so that bad ref aborted the loop and every skill after it (all three recoup-roster-*) never installed.

Verified on the Apache→OneRPM run (chat#1833): loading recoup-roster-list-artists returned "Skill not found. Available: recoup-platform-api-access, recoup-platform-email-helper."

Fix

• defaultGlobalSkillRefs.ts: recoup-platform-build-workspace → recoup-platform-build-os.
• installGlobalSkills.ts: best-effort per skill — console.error + continue instead of throw, so one bad ref can't block the rest.

Tests (TDD)

• New RED→GREEN test: installGlobalSkills continues past a failed skill, still attempts the rest, logs the failure, never throws.
• Full lib/skills suite green (49), tsc + eslint clean.

🤖 Generated with Claude Code

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Summary by cubic

Ensure all default sandbox skills install by fixing a renamed ref and making installs resilient. One bad ref no longer blocks the rest.

• Bug Fixes
  • Updated DEFAULT_GLOBAL_SKILL_REFS: recoup-platform-build-workspace → recoup-platform-build-os to stop npx skills add 404s.
  • Made installGlobalSkills best-effort: never throws; logs and continues so later skills (e.g., recoup-roster-*) still install.

Summary by CodeRabbit

• New Features

  • Updated the default platform setup to include the OS build skill instead of the workspace build skill.

• Bug Fixes

  • Skill installation now continues even if one item fails, allowing the rest of the setup to complete.
  • Failed installs are now reported in the console for easier troubleshooting.