Support Git repositories as Agent Plugin sources

[danielkov]

Summary

Kit Agent Plugins currently support path and checksum-pinned archive sources. Add a Git source so Kit can consume plugins distributed through Git repositories, including private or credentialed Git proxy endpoints.

Environment

• Kit: 0.1.119
• OS: macOS (Darwin, arm64)

Current limitation

A valid Agent Plugins repository exposed as a Git URL cannot be added directly to ~/.kit/config.toml. Users must separately download/extract an archive and configure it as a local path, or find a stable archive URL and checksum. Some plugin publishers intentionally expose a private backing repository through a credentialed Git proxy, so a forge archive URL is not available.

Expected behavior

Support a configuration along these lines:

[plugins.example]
source = "git"
url = "https://plugins.example.com/marketplace/<opaque-id>.git"
rev = "<commit-or-tag>"
subdir = "agent-plugins/example"

Suggested requirements:

• Support an immutable commit/tag pin for reproducible resolution.
• Support plugin packages at the repository root or a validated subdir.
• Cache by resolved revision and validate the package before activation.
• Use Git credential helpers or Kit's credential store for private sources; do not require inline URL credentials or print secrets in diagnostics.
• Define explicit refresh/update behavior for mutable refs.
• Retain the last valid checkout if a fetch or validation fails during a live reload.