feat(scripts): common.sh helpers (log_*, require_cmd, make_backup_dir)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scripts/lib/common.sh

@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+# Shared helpers for brain scripts
+# Source guard
+[ -n "${__BRAIN_COMMON_LOADED:-}" ] && return 0
+__BRAIN_COMMON_LOADED=1
+
+log_info()  { printf "[INFO]  %s\n" "$*" >&2; }
+log_warn()  { printf "[WARN]  %s\n" "$*" >&2; }
+log_error() { printf "[ERROR] %s\n" "$*" >&2; }
+
+require_cmd() {
+    local cmd="$1"
+    if ! command -v "$cmd" >/dev/null 2>&1; then
+        log_error "Required command not found: $cmd"
+        return 1
+    fi
+    return 0
+}
+
+make_backup_dir() {
+    local target="$1"
+    local ts
+    ts=$(date +%Y%m%d-%H%M%S)
+    local backup="${target%/}/.brain-backup-${ts}"
+    mkdir -p "$backup"
+    printf "%s" "$backup"
+}

scripts/tests/common-test.sh

@@ -0,0 +1,42 @@
+#!/usr/bin/env bash
+# Tests for scripts/lib/common.sh
+set -u
+SCRIPT_DIR="$(cd "$(dirname "$0")/.." && pwd)"
+source "$SCRIPT_DIR/lib/common.sh"
+
+FAILURES=0
+assert_eq() {
+    local expected="$1" actual="$2" name="$3"
+    if [ "$expected" = "$actual" ]; then
+        echo "PASS: $name"
+    else
+        echo "FAIL: $name (expected '$expected', got '$actual')"
+        FAILURES=$((FAILURES + 1))
+    fi
+}
+
+# Test 1: log_info writes to stderr
+output=$(log_info "test message" 2>&1 1>/dev/null)
+case "$output" in
+    *"test message"*) assert_eq "ok" "ok" "log_info goes to stderr" ;;
+    *) assert_eq "ok" "fail" "log_info goes to stderr" ;;
+esac
+
+# Test 2: require_cmd succeeds for existing command
+require_cmd ls >/dev/null 2>&1
+assert_eq "0" "$?" "require_cmd ls returns 0"
+
+# Test 3: require_cmd fails for missing command
+require_cmd this_command_definitely_does_not_exist_12345 >/dev/null 2>&1
+result=$?
+[ "$result" -ne 0 ] && assert_eq "0" "0" "require_cmd missing returns non-zero" || assert_eq "0" "1" "require_cmd missing returns non-zero"
+
+# Test 4: make_backup_dir creates dir
+tmpdir=$(mktemp -d)
+backup=$(make_backup_dir "$tmpdir")
+[ -d "$backup" ] && assert_eq "yes" "yes" "make_backup_dir creates directory" || assert_eq "yes" "no" "make_backup_dir creates directory"
+rm -rf "$tmpdir"
+
+echo "---"
+echo "Failures: $FAILURES"
+exit $FAILURES