Move git identity to an included ~/.gitconfig.local

~/.extra ran five `git config --global` writes on every shell startup, to
re-assert identity and signing after bootstrap.sh copies gitconfig over
~/.gitconfig. The dark-mode-notify agent fires on wake/unlock and runs
`pkill -usr1 zsh`, so every shell re-sources .zshrc — and therefore .extra —
simultaneously. `git config` locks with O_EXCL and has no retry or timeout for
config files, so the concurrent writes raced and printed:

    error: could not lock config file /Users/jonny/.gitconfig: File exists

Identity and signing now live in an untracked ~/.gitconfig.local, included
last from gitconfig so it wins over anything above. bootstrap.sh seeds it from
gitconfig.local.template only when absent, so re-runs never clobber the real
signing key. No git writes happen on shell startup at all now.

Verified: fully-resolved config is unchanged apart from the new include.path;
author and committer both resolve from config with no GIT_* env vars set;
existing commits still verify. 12 concurrent sources of .extra are silent,
where the old version produced 27 lock errors.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

bootstrap.sh

@@ -48,10 +48,19 @@ test -L $HOME/.config/nvim/lsp/phpactor.lua || ln -f -s $BASEDIR/neovim/lsp/phpa
 test -d $HOME/.claude || mkdir $HOME/.claude
 ln -f -s $BASEDIR/claude/statusline.isaacaudet.sh $HOME/.claude/statusline.sh
 
-# .gitconfig gets edited by .extra so we won't symlink it, but copy it
+# Copy rather than symlink, so an ad-hoc `git config --global` writes to $HOME
+# and not into the repo.
 echo "For compatibility we shall copy the global gitconfig"
 cp $BASEDIR/gitconfig $HOME/.gitconfig
 
+# Identity and signing live in ~/.gitconfig.local, which the above includes.
+# It is per-machine and untracked, so seed it from the template. Never
+# overwrite an existing one: it holds the real signing key.
+test -e $HOME/.gitconfig.local || {
+  echo "Seeding ~/.gitconfig.local from template — fill in your identity"
+  cp $BASEDIR/gitconfig.local.template $HOME/.gitconfig.local
+}
+
 # Copy the progs into the local bin dir
 rsync -av --chmod=+x $BASEDIR/bin/ $HOME/.local/bin/
 

gitconfig

@@ -87,3 +87,9 @@
     autoSquash = true
     autoStash = true
     updateRefs = true
+
+# Machine-local identity and signing config. Untracked, and included last so
+# it wins over anything above. Keeps `bootstrap.sh`'s copy of this file
+# non-destructive without needing to re-apply values on every shell startup.
+[include]
+    path = ~/.gitconfig.local

gitconfig.local.template

@@ -0,0 +1,23 @@
+# Machine-local git config, included from the end of ~/.gitconfig.
+#
+# This file is NOT tracked in the dotfiles repo — it is per-machine, and holds
+# the identity and signing key. bootstrap.sh copies this template into place
+# only if ~/.gitconfig.local does not already exist, so your real values are
+# never clobbered by a re-run.
+#
+# Uncomment and fill these in on a new machine. Do not skip this: git will not
+# refuse to commit. It auto-derives an identity from your username and hostname
+# (e.g. jonny@Jonnys-MacBook.local), prints a "configured automatically"
+# warning, exits 0, and does no signing at all.
+
+#[user]
+#    name = Your Name
+#    email = you@example.com
+#    signingkey = ssh-ed25519 AAAA...
+
+#[commit]
+#    gpgsign = true
+
+# Path to the signing program, if signing SSH-style via a password manager.
+#[gpg "ssh"]
+#    program = /Applications/1Password.app/Contents/MacOS/op-ssh-sign