feat: add global agent install

[PatrickSys]

Summary

• Add an npx-first global install path for reusable Workspine skills and native agent surfaces across Claude Code, OpenCode, Codex CLI, and qualified GitHub Copilot CLI targets.
• Keep repo-local setup on npx -y gsdd-cli init; npx -y gsdd-cli install --global writes only selected user agent homes and never bootstraps .planning/ in the current repo.
• Align the global layout with current vendor discovery: Claude uses ~/.claude/skills; OpenCode, Codex CLI, and Copilot CLI share portable skills under ~/.agents/skills; native command/agent files stay in each vendor home.
• Keep the public surface simple: no public runtime-probe flags, no install-time model sessions, and no repo-local model override leakage into global user homes.
• Add safe migration cleanup for old Workspine-managed private skill copies under OpenCode/Copilot homes, pruning only unchanged manifest-tracked files and blocking on user-modified files.

Public Surface

• Global install: npx -y gsdd-cli install --global --tools claude,opencode,codex,copilot or interactive target selection in a TTY.
• Repo-local repair: npx -y gsdd-cli health then npx -y gsdd-cli update inside a .planning/ workspace.
• Global repair/refresh: rerun npx -y gsdd-cli install --global --tools <targets>.
• Runtime probes remain internal pressure-harness behavior, not user-facing install flags.

Verification

• rtk node tests/gsdd.global-install-pressure.test.cjs
• rtk node tests/gsdd.init.test.cjs
• rtk npm test
• rtk git diff --check
• Isolated live smoke with temp HOME/USERPROFILE/vendor homes: confirmed Claude skill, shared .agents skill, OpenCode command/agent, Codex agent, Copilot agent, and no OpenCode/Copilot private skill duplicates.

Runtime Notes

• OpenCode honors OPENCODE_CONFIG_DIR for commands and agents; skills stay in the shared agent-compatible root.
• Codex and Copilot live probes now pin HOME and USERPROFILE during internal checks so they validate the isolated install, not the real user home.
• The branch was checked against official/current vendor behavior and the skills installer model; install availability is not promoted to equal runtime parity for Copilot.

[gemini-code-assist]

Code Review

This pull request updates the documentation and test suites to emphasize that no global installation is required for Workspine, promoting the use of npx -y gsdd-cli for initialization, health checks, and updates. It introduces several new sections to the README.md detailing the product, quickstart steps, configuration, and troubleshooting, while updating the test suite to validate these documentation changes. Feedback on the pull request highlights a significant duplication introduced in README.md between the new 'Getting Started' section and the pre-existing 'Get started' section, suggesting they be consolidated to keep the documentation clean.

Important

The consumer version of Gemini Code Assist on GitHub is being sunset. Starting June 18, 2026, new organization installations will be blocked, and all code review activity will officially cease on July 17, 2026.
For more details on the timeline and next steps, please review the Help Documentation.

[PatrickSys]

@codex review

[chatgpt-codex-connector]

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