Phase 17: Antigravity plugin bundle skeleton

[ProfRandom92]

Phase 17 implements the Antigravity Plugin Bundle Skeleton under the Git Safety Gate governance rules.

Scope:

• ctxt antigravity command skeleton
• Antigravity plugin templates
• skills/hooks/MCP/permissions/subagents/rules template surfaces
• Phase 17 documentation and report
• no live hooks
• no global install
• no MCP server implementation
• subagents advisory only
• no LLM judge
• no production/enterprise/compliance/certification claims
• no cryptographic-proof claims

[gemini-code-assist]

Code Review

This pull request implements the skeleton for the Antigravity plugin bundle (Phase 17), introducing the ctxt antigravity command with subcommands for exporting, validating skills, auditing hooks, and packaging plugins. It also adds local templates, documentation, and smoke tests for these features. The review feedback suggests using path.is_dir() instead of path.exists() to more robustly verify the local skills directory, and corrects a minor grammatical error in AGENTS.md.

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[gemini-code-assist]

Using path.is_dir() is more robust than path.exists() here because it ensures that the path is actually a directory before proceeding with the validation message, preventing false positives if a file with the same name exists.

Suggested change

	if path.exists() {
	if path.is_dir() {

[gemini-code-assist]

The verb should be plural ('require') to agree with the plural subject 'Network socket connections'.

Suggested change

	9. **Network Sandbox**: Network socket connections are denied by default and requires explicit phase permission.
	9. **Network Sandbox**: Network socket connections are denied by default and require explicit phase permission.