Agent skill file path uses client OS path instead of remote host path over Remote SSH

[pdebruin]

Problem

When using Copilot Chat with agent skills over Remote SSH (Windows client -> Linux remote), the agent receives the skill file path resolved using the client OS convention (Windows path), not the remote host filesystem path. The file read fails silently, and the agent falls back to degraded behavior without the skill context.

Reproduction

1. Install a Copilot agent plugin that defines a skill (e.g., via external.json in an extension pack -- no OS-specific paths in the definition)
2. Connect to a Linux remote host via Remote SSH from a Windows client
3. The skill/plugin is installed on the remote at ~/.copilot/installed-plugins/_direct/<publisher>--<name>/skills/<skill-name>/SKILL.md
4. Invoke the skill in Copilot Chat

Expected

The agent receives the skill file path relative to the remote host filesystem, e.g.:

/home/<user>/.copilot/installed-plugins/_direct/microsoft--Build-CLI/skills/microsoft-build/SKILL.md

Actual

The agent receives a Windows client path:

c:/Users/<user>/.vscode/agent-plugins/github.com/microsoft/Build-CLI/skills/microsoft-build/SKILL.md

This path does not exist on the Linux remote. The file read fails. The agent does not recover (no fallback search for the file on disk), and proceeds without the skill context.

Impact

The skill loaded by name and appeared in the available skills list, but its instructions were never read. In this case it was a Build session catalog skill -- the agent fell back to docs-only search and missed the entire session catalog (the primary output of the skill). The same file was read successfully by Copilot CLI running directly on the same Linux host.

Environment

• VS Code with Remote SSH extension
• Client: Windows
• Remote: Linux
• Copilot Chat with agent mode
• Plugin defined via external.json (no OS-specific paths in the plugin definition)

[y2kbugger]

I have same symptom, opposite operating systems: linux local, windows remote.
This could just be a symptom of using remotes in general and not mismatch specific.
in-ability to find skill files when using "remote tunnel" feature.

/troubleshoot output

Bug Report: Agent-plugin skill path breaks in mixed local/remote setup

In a mixed setup where the client machine is Linux and the workspace/remote target is Windows, a skill provided by an agent plugin is referenced using a client-local Linux path, but skill discovery on the active session only searches the remote/workspace Windows skill folders.

Result: the skill is visible in prompt metadata, but it does not behave like a normally discovered skill in the active session.

Environment

• Client OS: Linux
• Remote/workspace OS: Windows
• Remote coding: VS Code connected to a remote Windows workspace
• Workspace path example:
  • C:\Users\fakeuser\dev\FakeProject
• Client-local plugin path example:
  • /home/fakeuser/.vscode/agent-plugins/github.com/fakevendor/sqlir/agent-plugin/skills/sqlir/SKILL.md

Problem

A plugin-provided skill was available enough to appear in prompt context, but it was not part of normal skill discovery for the session.

The active session searched these skill folders:

• /C:/Users/fakeuser/.agents/skills
• /C:/Users/fakeuser/.copilot/skills
• /C:/Users/fakeuser/.claude/skills
• /c:/Users/fakeuser/dev/FakeProject/.agents/skills
• /c:/Users/fakeuser/dev/FakeProject/.github/skills
• /c:/Users/fakeuser/dev/FakeProject/.claude/skills

The plugin skill path was instead referenced as:

• /home/fakeuser/.vscode/agent-plugins/github.com/fakevendor/sqlir/agent-plugin/skills/sqlir/SKILL.md

That Linux path is client-local and does not match the remote Windows environment where discovery is happening.

Why this looks wrong

The session clearly distinguishes between:

• normal skill discovery from Windows/remote paths
• plugin skill metadata that points at a Linux/client path

That mismatch strongly suggests agent-plugin skills are not being resolved consistently in remote sessions.

Expected

Plugin-provided skills should either:

1. be fully discoverable and usable in the active remote session, or
2. be excluded if their backing path is not valid in that session, or
3. be copied/resolved into a session-accessible location before being advertised to the model

Actual

The skill was advertised to the model, but normal discovery did not include the plugin location used by that skill.

This makes plugin skills unreliable in local/remote mixed-OS setups.

Impact

This is especially confusing because the skill can appear to exist, but still not behave like a normally loaded skill. In practice this makes debugging skill behavior difficult and can look like the model is ignoring the skill.

Suggested fix

Please make agent-plugin skill resolution session-aware:

• normalize plugin skill paths for remote sessions
• avoid surfacing plugin skills whose files are not accessible in the active environment
• or include agent-plugin locations in the same discovery pipeline used for normal skills

Minimal repro shape

1. Install a Copilot agent plugin that provides a skill on a Linux client
2. Open a remote Windows workspace in VS Code
3. Start a chat session
4. Observe:
   • standard skill discovery uses Windows/remote paths
   • plugin skill references a Linux/client path
   • plugin skill is not treated like a normally discovered skill