Add disk space cleanup skill

dotfiles/agents/skills/disk-space-cleanup/SKILL.md

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+---
+name: disk-space-cleanup
+description: Investigate and safely reclaim disk space on this machine, especially on NixOS systems with heavy Nix, Rust/Haskell, Docker, and Podman usage. Use when disk is low, builds fail with no-space errors, /nix/store appears unexpectedly large, or the user asks for easy cleanup wins without deleting important data.
+---
+
+# Disk Space Cleanup
+
+Reclaim disk space with a safety-first workflow: investigate first, run obvious low-risk cleanup wins, then do targeted analysis for larger opportunities.
+
+## Execution Default
+
+- Start with non-destructive investigation and quick sizing.
+- Prioritize easy wins first (`nix-collect-garbage`, container prune, Cargo artifacts).
+- Propose destructive actions with expected impact before running them.
+- Run destructive actions only after confirmation, unless the user explicitly requests immediate execution of obvious wins.
+- Capture new reusable findings by updating this skill before finishing.
+
+## Workflow
+
+1. Establish current pressure and biggest filesystems
+2. Run easy cleanup wins
+3. Sweep Rust build artifacts in common project roots
+4. Investigate remaining heavy directories with `ncdu`/`du`
+5. Investigate `/nix/store` roots when large toolchains still persist
+6. Summarize reclaimed space and next candidate actions
+7. Record new machine-specific ignore paths or cleanup patterns in this skill
+
+## Step 1: Baseline
+
+Run a quick baseline before deleting anything:
+
+```bash
+df -h /
+df -h /home
+df -h /nix
+```
+
+Optionally add a quick home-level size snapshot:
+
+```bash
+du -xh --max-depth=1 "$HOME" 2>/dev/null | sort -h
+```
+
+## Step 2: Easy Wins
+
+Use these first when the user wants fast, low-effort reclaiming:
+
+```bash
+sudo -n nix-collect-garbage -d
+sudo -n docker system prune -a
+sudo -n podman system prune -a
+```
+
+Notes:
+- Add `--volumes` only when the user approves deleting unused volumes.
+- Re-check free space after each command to show impact.
+- Prefer `sudo -n` first so cleanup runs fail fast instead of hanging on password prompts.
+
+## Step 3: Rust Build Artifact Cleanup
+
+Target common roots first: `~/Projects` and `~/code`.
+
+Use `cargo-sweep` in dry-run mode before deleting:
+
+```bash
+nix run nixpkgs#cargo-sweep -- sweep -d -r -t 30 ~/Projects ~/code
+```
+
+Then perform deletion:
+
+```bash
+nix run nixpkgs#cargo-sweep -- sweep -r -t 30 ~/Projects ~/code
+```
+
+Alternative for toolchain churn cleanup:
+
+```bash
+nix run nixpkgs#cargo-sweep -- sweep -r -i ~/Projects ~/code
+```
+
+Recommended sequence:
+
+1. Run `-t 30` first for age-based stale builds.
+2. Run a dry-run with `-i` next.
+3. Apply `-i` when dry-run shows significant reclaimable space.
+
+## Step 4: Investigation with `ncdu` and `du`
+
+Avoid mounted or remote filesystems when profiling space. Load ignore patterns from `references/ignore-paths.md`.
+
+Use one-filesystem scans to avoid crossing mounts:
+
+```bash
+ncdu -x "$HOME"
+sudo ncdu -x /
+```
+
+When excluding known noisy mountpoints:
+
+```bash
+ncdu -x --exclude "$HOME/keybase" "$HOME"
+sudo ncdu -x --exclude /keybase --exclude /var/lib/railbird /
+```
+
+If `ncdu` is missing, use:
+
+```bash
+nix run nixpkgs#ncdu -- -x "$HOME"
+```
+
+## Step 5: `/nix/store` Deep Dive
+
+When `/nix/store` is still large after GC, inspect root causes instead of deleting random paths.
+
+Useful commands:
+
+```bash
+nix path-info -Sh /nix/store/* 2>/dev/null | sort -h | tail -n 50
+nix-store --gc --print-roots
+```
+
+Avoid `du -sh /nix/store` as a first diagnostic; it can be very slow on large stores.
+
+For repeated GHC/Rust toolchain copies:
+
+```bash
+nix path-info -Sh /nix/store/* 2>/dev/null | rg '(ghc|rustc|rust-std|cargo)'
+nix-store --gc --print-roots | rg '(ghc|rust)'
+```
+
+Resolve why a path is retained:
+
+```bash
+/home/imalison/dotfiles/dotfiles/lib/functions/find_store_path_gc_roots /nix/store/<store-path>
+nix why-depends <consumer-store-path> <dependency-store-path>
+```
+
+Common retention pattern on this machine:
+
+- Many `.direnv/flake-profile-*` symlinks under `~/Projects` and worktrees keep `nix-shell-env`/`ghc-shell-*` roots alive.
+- Quantify before acting:
+
+```bash
+find ~/Projects -type l -path '*/.direnv/flake-profile-*' | wc -l
+find ~/Projects -type d -name .direnv | wc -l
+```
+
+- If counts are high and the projects are inactive, propose targeted `.direnv` cleanup for user confirmation.
+
+## Safety Rules
+
+- Do not delete user files directly unless explicitly requested.
+- Prefer cleanup tools that understand ownership/metadata (`nix`, `docker`, `podman`, `cargo-sweep`) over `rm -rf`.
+- Present a concise “proposed actions” list before high-impact deletes.
+- If uncertain whether data is needed, stop at investigation and ask.
+
+## Learning Loop (Required)
+
+Treat this skill as a living playbook.
+
+After each disk cleanup task:
+
+1. Add newly discovered mountpoints or directories to ignore in `references/ignore-paths.md`.
+2. Add validated command patterns or caveats discovered during the run to this `SKILL.md`.
+3. Keep instructions practical and machine-specific; remove stale guidance.

dotfiles/agents/skills/disk-space-cleanup/agents/openai.yaml

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+interface:
+  display_name: "Disk Space Cleanup"
+  short_description: "Find safe disk-space wins on NixOS hosts"

dotfiles/agents/skills/disk-space-cleanup/references/ignore-paths.md

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+# Ignore Paths for Disk Investigation
+
+Use this file to track mountpoints or directories that should be excluded from `ncdu`/`du` scans because they are remote, special-purpose, or noisy.
+
+## Known Ignores
+
+- `$HOME/keybase`
+- `/keybase`
+- `/var/lib/railbird`
+- `/run/user/*/doc` (FUSE portal mount; machine-specific example observed: `/run/user/1004/doc`)
+
+## Discovery Commands
+
+List mounted filesystems and spot special mounts:
+
+```bash
+findmnt -rn -o TARGET,FSTYPE,SOURCE
+```
+
+Target likely remote/special mounts:
+
+```bash
+findmnt -rn -o TARGET,FSTYPE,SOURCE | rg '(keybase|fuse|rclone|s3|railbird)'
+```
+
+## Maintenance Rule
+
+When a disk cleanup run encounters a mount or path that should be ignored in future runs, add it here immediately with a short note.