docs: record disk cleanup findings

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

@@ -174,6 +174,10 @@ Machine-specific heavy hitters seen in practice:
   - Validated cleanup pattern: stop `gitea-runner-nix.service`, remove cache/work directories under `/var/lib/private/gitea-runner` (`.cache`, `.gradle`, `action-cache-dir`, `workspace`, stale nested `gitea-runner`, and nested `nix/.cache`/`nix/.local`), recreate `action-cache-dir`, `workspace`, and `.cache` owned by `gitea-runner:gitea-runner`, then restart the service.
   - Preserve registration/config-like files such as `/var/lib/private/gitea-runner/nix/.runner`, `/var/lib/private/gitea-runner/nix/.labels`, `/var/lib/private/gitea-runner/.docker/config.json`, and SSH/Kube material.
 - `~/Projects/*/target` directories can dominate home usage. Recent example candidates included stale `target/` directories under `scrobble-scrubber`, `http-client-vcr`, `http-client`, `subtr-actor`, `http-types`, `subtr-actor-py`, `sdk`, and `async-h1`.
+- 2026-05-26 cleanup: deleting explicit Cargo-backed targets under `~/Projects/{keepbook,subtr-actor,rlru,rocket-sense,boxcars,rumno}` plus stale `subtr-actor/.worktrees/*/target` reclaimed about 65G by helper sizing and moved `/` from 100% used to 89% used. A final all-depth scan left no `~/Projects` Rust `target/` directories over 500M.
+- 2026-05-26 cleanup: when `cargo test` is actively running in `~/Projects/subtr-actor`, leave `subtr-actor/target` alone and delete only inactive Cargo-backed targets. Deleting `keepbook`, `rlru`, `rocket-sense`, `rumno`, and stale `subtr-actor/.worktrees/*/target` reclaimed about 24.5G by helper sizing.
+- 2026-05-26 cleanup: `~/Projects/nixpkgs/.worktrees/*/result` symlinks pinned several GiB of Nix closures, and clean registered nixpkgs worktrees were about 460M each. Removing stale `result` symlinks, running GC, and removing clean worktrees while preserving dirty ones moved `/` from 100% used to about 90% used.
+- 2026-05-27 cleanup: under `~/Projects`, `hypr-workspace-history/target` can be a Rust-style build cache even though the guarded helper rejects it because no `Cargo.toml` is present; inspect and remove that explicit cache manually if present. Preserve `~/Projects/Hyprland/src/layout/target`, which is source code, not a build artifact.
 
 ## Step 5: `/nix/store` Deep Dive
 
@@ -209,6 +213,7 @@ Common retention pattern on this machine:
 - `find_store_path_gc_roots` is especially useful for proving GHC retention: many large `ghc-9.10.3-with-packages` paths are unique per project, while the base `ghc-9.10.3` and docs paths are shared.
 - NixOS system generations and a repo-root `nixos/result` symlink can pin multiple Android Studio and Android SDK versions. Check `/nix/var/nix/profiles/system-*-link`, `/run/current-system`, `/run/booted-system`, and `~/dotfiles/nixos/result` before assuming Android paths are pinned by project shells.
 - `~/Projects/railbird-mobile/.direnv/flake-profile-*` can pin large Android SDK system images. Removing stale direnv profiles there is a more targeted first step than deleting Android store paths directly.
+- 2026-05-27 Railbird GHC audit: the Railbird backend flake did not explicitly reference Haskell, but its dev shell had derivation-time GHC edges through `inputs.secrets.devShells.${system}.default -> agenix -> shellcheck -> ShellCheck -> ghc` and through `shell-packages.nix`'s `rdma-core -> pandoc-cli -> ghc`. Railbird Mobile had similar non-app-code GHC edges through `inputs.secrets`/`agenix` and `nixGLIntel -> shellcheck`. The `railbird/gql` and `railbird-mobile/src/gql` shells did not show GHC edges in their derivation graphs, only Rust/Cargo build tooling from packages such as `just`.
 - For a repeatable `/nix/store` `ncdu` snapshot without driving the TUI, export and inspect it:
 
 ```bash