Import josh-sync from subrepo/main

Sync-Origin: import/josh-sync/20260528-041502

lib/core.sh

@@ -0,0 +1,29 @@
+#!/usr/bin/env bash
+# lib/core.sh — Foundation: logging, exit codes, git environment isolation
+#
+# Source this first. All other modules depend on it.
+
+set -euo pipefail
+
+# ─── Exit Codes ─────────────────────────────────────────────────────
+
+readonly E_GENERAL=1
+
+# ─── Logging ────────────────────────────────────────────────────────
+# All log output goes to stderr. Sync functions use stdout for return values.
+
+log() {
+  local level="$1"; shift
+  echo "$(date -u +%H:%M:%S) [${level}] $*" >&2
+}
+
+die() { log "FATAL" "$@"; exit "$E_GENERAL"; }
+
+# ─── Git Environment Isolation ──────────────────────────────────────
+# Prevent user/system config from interfering with sync operations.
+# Safe because josh-sync always runs as a subprocess, never sourced into
+# an interactive shell.
+
+export GIT_CONFIG_GLOBAL=/dev/null
+export GIT_CONFIG_SYSTEM=/dev/null
+export GIT_TERMINAL_PROMPT=0