chore: add shared pre-commit gofmt hook

.githooks/pre-commit

@@ -0,0 +1,21 @@
+#!/bin/sh
+# Pre-commit hook: block the commit if any staged Go file is not gofmt-clean.
+#
+# Enable once per clone:
+#     git config core.hooksPath .githooks
+#
+# This mirrors the CI gofmt check so formatting failures surface locally
+# instead of after a push. It only inspects staged Go files, so it stays fast.
+
+# Added/Copied/Modified staged .go files (skip deletions).
+gofiles=$(git diff --cached --name-only --diff-filter=ACM -- '*.go')
+[ -z "$gofiles" ] && exit 0
+
+unformatted=$(gofmt -l $gofiles)
+if [ -n "$unformatted" ]; then
+	echo "gofmt: these staged files are not formatted:" >&2
+	echo "$unformatted" | sed 's/^/  /' >&2
+	echo "" >&2
+	echo "Fix with:  gofmt -w $unformatted" >&2
+	exit 1
+fi

README.md

@@ -54,6 +54,21 @@ Full instructions:
 | `internal/proc` | Cross-platform helper that hides child-process console windows on Windows |
 | `internal/version` | Version resolution from `-ldflags` override or embedded VCS info |
 | `skills/` | `/distill` and `/distill-apply` Claude Code skills |
+| `.githooks/` | Shared git hooks (pre-commit gofmt check) |
+
+## Development
+
+The repo ships a pre-commit hook that runs the same `gofmt` check as CI, so
+formatting problems surface locally instead of after a push. Enable it once per
+clone:
+
+```sh
+git config core.hooksPath .githooks
+```
+
+It only inspects staged `.go` files and blocks the commit if any are not
+gofmt-clean, printing the `gofmt -w …` command to fix them. (`go vet` and the
+test suite stay in CI, which runs them across Linux/macOS/Windows.)
 
 ## Releasing