fredsystems

Use ONLY when working in the fred/nixos flake repository (the NixOS configuration at ~/GitHub/nixos with hosts/linux/, modules/, profiles/, features/, home-profiles/, flake.nix, flake.lock) and a change has been made that needs verification before push. This NixOS repo has no `cargo test` equivalent -- verification is `nix eval` on the impacted hosts' system.build.toplevel.drvPath. This skill computes which hosts are impacted from the git diff (mirroring the CI's path-based filter and flake.lock input-aware parser) and runs the evals locally so push-time CI failures are caught beforehand.

Use ONLY in the fred/nixos flake repo when adding, reverting, or reasoning about a TEMPORARY workaround that exists solely because of an unfixed upstream bug -- a package overlay (`overrideAttrs`, `doCheck = false`, `postPatch`, CFLAGS pins), a `permittedInsecurePackages` entry, a polkit/module workaround, a disabled feature (`*.enable = false`), or a gh-dash/app keybind hack. Covers the `.github/tracked-upstream-fixes.json` manifest, the `check-upstream-fixes.sh` checker, the `track-upstream-fixes.yaml` workflow, choosing the right check type (issue-closed vs release-contains-commit vs pkgs-min-version vs nixpkgs-pin-contains-commit), and the FIXME-comment convention that ties code to a manifest entry.

Use when editing `.rs` files or `Cargo.toml`, adding/updating a cargo dependency, running `cargo`, `cargo add`, `cargo clippy`, `cargo test`, `cargo xtask`, or before declaring any Rust change complete. Codifies the "lints maxed, no bypasses, no panics in production" Rust policy plus the dependency-hygiene rules (alphabetical sort, full semver pinning) that apply across every Rust crate in fred's repos.

Use when a git commit is rejected by pre-commit hooks, when the user mentions "pre-commit", "lint failed", "hook failed", or before running `git commit` in any of fred's repos that share the fredsystems/precommit-base ruleset (nixos, freminal, docker-acarshub, and downstream projects). Covers diagnosing which hook fired, fixing the underlying issue (never the symptom), and the strict no-bypass policy.

Use when editing `.nix` files in any of fred's flake-managed repos (nixos, freminal, docker-acarshub, and downstream). Codifies the active, strict Nix lint stack — `nixfmt` (auto-format), `statix check` (anti-patterns), `deadnix --fail` (unused bindings) — that runs on every `.nix` commit via the `fredsystems/precommit-base` pre-commit ruleset. Lists the common rejections (empty `{ ... }:` patterns, unused `let` / function args, `with` abuse, anti-patterns flagged by statix) and how to write Nix that passes on the first commit. No bypasses, no per-file disables without a real reason.

Use whenever writing or editing any `.md` / `.mdx` / `.markdown` file (AGENTS.md, agents.md, README.md, agent-docs/*.md, SKILL.md frontmatter bodies, RFCs, design docs, anything). Codifies the markdownlint rules that bite fred's repos most often (MD031, MD040, MD024, MD058, MD012, MD041), the table-column-width rule, the no-emoji-in-tables rule, and the pre-commit fix loop. Prevents the common "pre-commit rejected your commit because of trailing whitespace / missing language tag / unbalanced table" round trip.

Use when editing `.ts` or `.tsx` files, when running `tsc`, `biome`, `eslint`, `vitest`, `playwright`, or `npm`/`pnpm`/`yarn` test/lint commands in any of fred's TypeScript projects. Codifies the strict-mode, no-`any`, no-`@ts-ignore`, explicit-return-types, structured-logger policy.

Use ONLY when working in the fred/nixos flake repository AND the task is to add (or remove) a flake input in flake.nix. Walks the four-location sync requirement, the `# CI:` comment convention, and the post-add verification that confirms CI will rebuild the right host set when the new input changes.

Use ONLY when working in the freminal repository AND touching the rendering pipeline, PTY I/O, buffer operations, ANSI parser, or `build_snapshot()`. Names exactly which benchmark file and benchmark IDs cover each performance-sensitive area of freminal. The generic before/after procedure, regression threshold, and recording format live in the shared `performance-benchmarks` skill — this skill is the freminal-specific catalog that skill points back to.

Use ONLY when working in the freminal repository AND about to open a pull request, finalize a change, or declare a task done — especially any change touching `#[cfg(windows)]` / `#[cfg(target_os = "windows")]` code, the vendored `portable-pty` crate, cross-platform path or filesystem logic, threads/closures/`Send` bounds, or anything else that compiles differently on Windows. Mandates running `cargo xtask check-windows` (clippy for the x86_64-pc-windows-gnu target) before the PR, so Windows-only compile errors and lints are caught locally instead of only on the `windows-latest` CI job. Also states what this gate does NOT catch (runtime failures) and where those are caught instead.

Use ONLY when working in the freminal repository AND changing task or version status in Documents/MASTER_PLAN.md — most importantly when a task's PR merges, when starting a task branch, or any time you edit MASTER_PLAN.md. Codifies the one-directional status lifecycle (Stub/Planned -> In progress -> Pending merge -> Complete), the mandatory merge-time transition that gets forgotten, the two-tables-must-agree invariant (Task Summary Status column vs. Completion Tracking dates), and the main-lag caveat for long-running integration branches like v0.11.0-kitty.

Use ONLY in the freminal repository when activating a version from MASTER_PLAN.md whose plan document is a stub (no per-subtask breakdown), or when fleshing out / decomposing any version's tasks into implementable subtasks. Codifies the just-in-time planning policy (don't decompose far-future versions; flesh a version out at activation against the real code), the Sonnet-sized subtask shape (scope, deliverable, verification, prohibitions, stop condition), and the Opus-orchestrates / Sonnet-implements / Opus-reviews division of labour. Pairs with freminal-orchestrator-protocol (planning-time companion to that execution-time skill).

Use ONLY when working in the freminal repository AND adding, editing, or debugging a GUI modal, dialog, overlay, popup, or any in-window widget that contains a focusable input (a TextEdit, search box, name field, filter box, etc.). Triggers on "my dialog doesn't accept typing", "focus bounces back to the terminal", "the modal renders but I can't type in it", "Escape/Enter does nothing in the dialog", or creating a new egui::Window/Area on the terminal surface. Codifies the ui_overlay_open registration + lock_focus(true) + per-frame request_focus pattern that every working modal uses, and that every new modal forgets.

Use ONLY when working in the freminal repository AND adding, renaming, or removing a configuration option (a field on `Config` or any of its section structs in `freminal-common/src/config.rs`, e.g. a new `[notifications]`/`[command_blocks]` key or a whole new section). Codifies the mandatory wiring checklist that prevents the "user sets it in config.toml but it silently does nothing" bug class — the `ConfigPartial` / `apply_partial` omission that dropped `[notifications] enabled = true` (fix 76.4a).

Use ONLY when working in the freminal repository (the Rust terminal emulator at ~/GitHub/freminal with crates freminal, freminal-terminal-emulator, freminal-buffer, freminal-common, freminal-windowing, xtask). Triggers on architecture-affecting changes: anything touching the GUI/PTY split, the ArcSwap snapshot transport, the channel-based input system, crate dependency boundaries, or `TerminalEmulator` / `TerminalSnapshot` / `ViewState`. Codifies the post-refactor lock-free architecture invariants.

Use ONLY when working in the freminal repository AND changing the ANSI parser, terminal handler, or renderer in a way that adds, removes, or alters support for an escape sequence (C0/C1, ESC, CSI, OSC, DCS, APC, DEC mode, standard mode, charset, or renderer-side consumption). Mandates the dual-document update: ESCAPE_SEQUENCE_COVERAGE.md (status table) and ESCAPE_SEQUENCE_GAPS.md (gap roadmap), with the "Last updated" header and Planned column maintenance.