.claude/tasks/0015-git-module.md

@@ -10,8 +10,26 @@ It is a `Module` rather than base plumbing because a `Host` that should not carr
 
 ## Acceptance criteria
 
-- [ ] A git `Module` following the `Enable convention` exists and is enabled on `neogaia`
-- [ ] The commit identity is configured through home-manager and matches the one used in existing history
-- [ ] `nix flake check` builds the `neogaia` toplevel
-- [ ] Manual confirmation: committing in a repository outside this checkout succeeds with no per-command identity override
-- [ ] The stale note in the project's agent instructions claiming git identity is unconfigured is corrected, since commits already work here through repository-local configuration
+- [x] A git `Module` following the `Enable convention` exists and is enabled on `neogaia`
+- [x] The commit identity is configured through home-manager and matches the one used in existing history
+- [x] `nix flake check` builds the `neogaia` toplevel
+- [x] Manual confirmation: committing in a repository outside this checkout succeeds with no per-command identity override
+- [x] The stale note in the project's agent instructions claiming git identity is unconfigured is corrected, since commits already work here through repository-local configuration
+
+## Implementation Notes
+
+`programs.git.userName`/`userEmail` are renamed in this home-manager pin and emit an obsolete-option trace.
+The module uses `settings.user.name`/`settings.user.email`.
+Do not "fix" it back.
+
+The commit name is the literal `"alexion"` rather than `config.user.name`, which review raised as duplication.
+A Unix login and a commit display name are separate concepts that merely coincide here, so binding them would let a host overriding its login silently rewrite the operator's commit identity.
+
+The manual confirmation was met against the built configuration, not the running machine: `nixos-rebuild switch` needs sudo and has not run, so `~/.config/git/config` does not yet exist on `neogaia`.
+The generated gitconfig was built from the `neogaia` toplevel and a commit driven under `env -i` with a scratch `HOME`, producing `alexion <contact@alexion.dev>` with no per-command override.
+This proves the derivation rather than the deployment, and the live check remains owed at the next rebuild.
+
+Review surfaced an unanticipated hazard that proved harmless.
+Home-manager writes `~/.config/git/config`, while an undeclared `~/.gitconfig` also exists and outranks it per key.
+It holds only a `tea` credential helper and no `user.*`, so it does not shadow the identity, confirmed by re-running the commit test with both files present.
+Declaring that credential helper is a reasonable follow-up, since it will not survive a reimage.

CLAUDE.md

@@ -36,9 +36,11 @@ The domain model (Host, Module, Skeleton, Auto-loader, Enable convention, overla
   Both were true only while the machine still ran CachyOS against a distro Nix daemon.
 - The substituters a `nix build` fetches from are the **daemon's** (`/etc/nix/nix.conf`), *not* the `nix.settings` of the config being built — those only govern the built system.
   The two coincide here because the dev host runs this flake; they diverge on any machine that does not.
-- Git identity is not declared in the flake — there is no `programs.git` — so it must be set by hand before the first commit on a fresh machine.
-  The July 2026 reimage confirmed this: it wiped the hand-written `~/.gitconfig`, and the next commit failed with `Author identity unknown`, auto-detecting `alexion@neogaia.(none)`.
-  It now lives in this checkout's `.git/config`, which reaches no other machine and does not survive the next reimage either; history uses `alexion <contact@alexion.dev>`.
+- Git identity is declared in the flake by `modules/git.nix`, which writes `alexion <contact@alexion.dev>` — the identity all history uses — on any host enabling `modules.git`.
+  Once such a host has been rebuilt, a checkout on it needs no hand-written identity and keeps one across a reimage.
+  Two things mask a broken module, so neither is evidence it works: this checkout's `.git/config` carries the same identity, and home-manager writes `~/.config/git/config` while a `~/.gitconfig` also exists and outranks it per key.
+  That `~/.gitconfig` holds only a `tea` credential helper and no `user.*`, so it does not shadow the identity today, but it is undeclared and will not survive a reimage.
+  Verify the module by committing in a repository outside this checkout.
 - The primary build/verify seam for any Host is `nix flake check`, which builds `checks.x86_64-linux.<host>` (the system toplevel); cheap targeted checks use `nix eval .#nixosConfigurations.<host>.config...`.
 - A flake only sees **git-tracked** files, so a new file that has not been `git add`ed is invisible to evaluation even though it exists on disk.
   The failure names the path and reads as if the file were missing: `error: Path 'secrets/shared.yaml' does not exist in Git repository`.

hosts/neogaia/default.nix

@@ -36,6 +36,7 @@
   modules.fish.enable = true;
   modules.fish.defaultShell = true;
 
+  modules.git.enable = true;
   modules.tmux.enable = true;
   modules.nvim.enable = true;
   modules.claude-code.enable = true;

modules/git.nix

@@ -0,0 +1,25 @@
+{
+  config,
+  lib,
+  ...
+}:
+# git for the primary user, configured through home-manager.
+let
+  cfg = config.modules.git;
+  user = config.user.name;
+in
+{
+  options.modules.git.enable =
+    lib.mkEnableOption "git for the primary user, carrying the operator's commit identity";
+
+  config = lib.mkIf cfg.enable {
+    home-manager.users.${user}.programs.git = {
+      enable = true;
+
+      # Git will not guess a name and address from the login and hostname.
+      # Without these a commit fails outright with `Author identity unknown`.
+      settings.user.name = "alexion";
+      settings.user.email = "contact@alexion.dev";
+    };
+  };
+}