Add an everyday check command and contributor test map

scripts/check.sh

@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+repository_dir=$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")/.." && pwd)
+cd "$repository_dir"
+
+# Use the installed toolchain unless the caller explicitly selects another.
+# Toolchains and dependencies must already be available locally.
+export GOTOOLCHAIN=${GOTOOLCHAIN:-local}
+export GOPROXY=off
+go version
+
+go_files=()
+while IFS= read -r -d '' go_file; do
+  if [[ -f "$go_file" ]]; then
+    go_files+=("$go_file")
+  fi
+done < <(git ls-files --cached --others --exclude-standard -z -- '*.go')
+if ((${#go_files[@]})); then
+  unformatted=$(gofmt -l -- "${go_files[@]}")
+  if [[ -n "$unformatted" ]]; then
+    printf 'gofmt required for:\n%s\n' "$unformatted" >&2
+    exit 1
+  fi
+fi
+
+git diff --check HEAD --
+while IFS= read -r -d '' candidate_file; do
+  # --no-index returns 1 for differing content even when whitespace is clean;
+  # whitespace errors return 2. Preserve other failures as well.
+  git diff --no-index --check -- /dev/null "$candidate_file" || {
+    check_status=$?
+    if ((check_status != 1)); then
+      exit "$check_status"
+    fi
+  }
+done < <(git ls-files --others --exclude-standard -z)
+
+go test ./...
+go vet ./...
+go build ./...