nixos-input-category-sync

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name: nixos-input-category-sync description: Use ONLY when working in the fred/nixos flake repository AND editing flake.nix inputs, flake.lock entries, .github/workflows/ci-linux.yaml, or the nixos-eval-impacted-hosts skill's script. Codifies the four-place sync invariant: every flake input must be classified consistently in (1) the # CI: comment in flake.nix, (2) the input-to-category table in agents.md, (3) the input_category bash associative array in ci-linux.yaml, and (4) the INPUT_CATEGORY array in scripts/impacted-hosts.sh of the nixos-eval-impacted-hosts skill.

NixOS: keep flake-input CI category in sync across four locations

The CI in this repo decides which hosts to rebuild based on which flake input changed in flake.lock. That decision is driven by a hand-maintained input-to-category mapping that lives in four places. They must agree, or CI will either over-build (wasting machine time) or under-build (missing required rebuilds, which is worse).

The four sync points

#	Location	Form
1	flake.nix	# CI: <category> comment immediately above each input declaration
2	agents.md (this repo)	The "Input-to-category mapping" markdown table
3	.github/workflows/ci-linux.yaml	The input_category bash associative array in the Detect changed paths step
4	.opencode/skills/projects/nixos-eval-impacted-hosts/scripts/impacted-hosts.sh	The INPUT_CATEGORY bash associative array

Valid categories

Category	Meaning
global	All Linux hosts rebuild
desktop	Only desktop hosts rebuild
server	Only server hosts rebuild
desktop+fredhub	All desktops rebuild, plus fredhub (the one server that pulls a package from unstable)
skip	No Linux rebuild (e.g. macOS-only inputs, dev tooling)

Unknown / new inputs default to global in all four places. That is the safe fallback -- it may over-build but never under-builds.

When you must update all four

• Adding a new flake input (see also: nixos-add-flake-input skill).
• Removing a flake input.
• Recategorizing an existing input (e.g. a server suddenly starts pulling a package from a previously desktop-only input).
• Renaming an input.

Verification

1. After editing, the four locations must agree on every input. A one-shot check:

   # Inputs declared in flake.nix (root-level inputs only)
   grep -E '^\s+\w[\w-]*\.url' flake.nix | awk -F. '{print $1}' | tr -d ' '
   

   Cross-reference against the keys in the input_category arrays in the two scripts and the table in agents.md. A missing entry in any of those falls back to global -- usually safe, occasionally wasteful.

2. Run the impacted-hosts script against a synthetic flake.lock change for the new input to confirm the category is honored. The easiest way: bump the input via nix flake update <input>, commit, then run:

   ./.opencode/skills/projects/nixos-eval-impacted-hosts/scripts/impacted-hosts.sh HEAD~1
   

   The output should match the category you intended.

When to stop and ask

• The category is genuinely ambiguous (e.g. an input is used by both desktops and one server in a way that doesn't cleanly map). Default to global and surface the situation to the user; do not invent a new category without discussion.
• An input's classification needs to change because of an unrelated refactor (e.g. a server stops pulling unstable). That's a separate PR with its own justification, not a drive-by during another change.