fix(summon): restore skill supporting files and directory path in load output

[angiejones]

Summary

When the unified summon extension replaced skills_extension in v1.25.0 (#6964), skill loading stopped communicating the skill directory path and supporting files (scripts, templates, etc.) to the agent. This caused the agent to load the skill content successfully but then have no idea where bundled scripts live, leading it to search the entire filesystem.

Restores the old behavior by collecting supporting files during skill discovery and including the skill directory + file listing in the load output.

Type of Change

• Bug fix
• Feature
• Refactor / Code quality
• Performance improvement
• Documentation
• Tests
• Security fix
• Build / Release
• Other (specify below)

AI Assistance

• This PR was created or reviewed with AI assistance

Testing

• All 9 existing summon unit tests pass
• New test_skill_supporting_files_discovered test verifies skills with bundled files get their directory path and supporting files populated correctly

Related Issues

Regression introduced in #6964

[Copilot]

Pull request overview

This PR fixes a regression introduced in #6964 where skill loading stopped communicating the skill directory path and supporting files to the agent. After the unified summon extension replaced the old skills_extension, skills would load successfully but the agent wouldn't know where bundled scripts and templates were located.

Changes:

• Added supporting_files field to Source struct to track supplementary files (scripts, templates, etc.)
• Implemented find_supporting_files() to discover supporting files in skill directories (recursing one level into subdirectories)
• Modified skill discovery to store the skill directory path instead of the SKILL.md file path, and populate supporting files list
• Updated load output to display skill directory path and list of available supporting files
• Added comprehensive test coverage for the new functionality

[michaelneale]

good catch @angiejones.

I wonder what other agents do - I guess it is convenient to list them in one go like this (could also just put it to root of dir and let whatever FS tool find it - pi does that, but this way is probably snappier, as long as we don't blow up the context with content of files but it should be reading them progressively on demand still).

[angiejones]

good catch @angiejones.

I wonder what other agents do - I guess it is convenient to list them in one go like this (could also just put it to root of dir and let whatever FS tool find it - pi does that, but this way is probably snappier, as long as we don't blow up the context with content of files but it should be reading them progressively on demand still).

yeah, followed the spec to do the 3 tier progressive disclosure. load output would be something like

## Supporting Files

Skill directory: /path/to/.goose/skills/my-skill

The following supporting files are available:
- myscript.sh
- templates/report.txt

Use the file tools to read these files or run scripts as directed.