Make /instructions opt-out persistent (per-repo), instead of resetting every session

[DmitriyShepelev]

Describe the feature or problem you'd like to solve

Copilot CLI already lets me disable instructions files for a session via /instructions. The problem is it's not persistent — the moment I start a new session in the same repo, all the auto-discovered instructions files (AGENTS.md, nested AGENTS.md, .github/copilot-instructions.md, parent-directory AGENTS.md, etc.) are loaded again, and I have to re-run /instructions to turn them off every single time.

For repos where I always want certain instructions files disabled, repeating this every session is tedious and easy to forget. I want my /instructions opt-out choices to be remembered per-repository so they persist across sessions.

Proposed solution

Persist the /instructions disable state on a per-repository basis so it's automatically reapplied on every new session in that repo.

Possible approaches:

• A "remember this" / "always" option in the /instructions UI that writes the choice to user-level config (e.g. ~/.copilot/config) keyed by repo path/remote.
• A persistent flag, e.g. /instructions disable AGENTS.md --persist, or a config command like copilot config set instructions.disabled "AGENTS.md" --repo ..
• On session start, automatically apply the saved per-repo disable list and show which files were loaded vs. skipped.
• Ability to clear/re-enable later (e.g. /instructions reset or removing the config entry).

Benefits to Copilot CLI and its users:

• Removes repetitive manual opt-out every session.
• Stable, predictable context per repo → better responses and fewer wasted tokens.
• Works in shared repos where I can't delete instructions files I didn't author.

Example prompts or workflows

1. In /instructions, toggle off AGENTS.md and choose "remember for this repo" → next session it's already disabled, no action needed.
2. copilot config set instructions.disabled "AGENTS.md" --repo . → Permanently disables that file for the current repo across all future sessions.
3. copilot config set instructions.enabled false --repo ./vendored-project → Persistently disables ALL auto-discovered instructions files for that repo.
4. Start a session in a repo with saved opt-outs → banner shows "Skipped (persisted): AGENTS.md, src/AGENTS.md".
5. /instructions reset → clears the persisted opt-out and resumes loading instructions normally.

Additional context

• Current behavior: /instructions works, but only for the active session — the opt-out is forgotten on the next run, so I re-disable the same files every time.
• Instructions are auto-discovered from the repo AND ancestor directories, so even a parent-folder AGENTS.md (e.g. in a OneDrive/home directory above the repo) gets loaded — making a persistent per-repo opt-out especially useful.
• Preference: scope the persistence per-repository (keyed by repo path or git remote), with an option for global defaults.
• Nice-to-have: a command to list discovered instructions files and their persisted enabled/disabled state.