Initial project outline

- package.json (ESM, bin entry)
- bin/delta-backup.js — entrypoint
- lib/args.js — CLI arg parsing via Node parseArgs
- lib/config.js — config file merging + required path guards
- lib/spawn.js — safe process spawning (no shell strings)
- lib/state.js — sequence number + phase state management
- lib/backends/zstd.js — zstd delta backend
- lib/backends/index.js — backend registry
- lib/commands/run.js — full run skeleton (phases 1-3 wired, 4-6 stubbed)
- lib/commands/status.js — status command

lib/args.js

@@ -0,0 +1,53 @@
+/**
+ * CLI argument parsing — no external deps, uses Node's parseArgs.
+ */
+import { parseArgs as nodeParseArgs } from 'util';
+
+const HELP = `
+Usage: delta-backup [options] <command>
+
+Commands:
+  run       Full backup run (clear PEND, rsync, delta, commit, promote)
+  status    Show current state
+
+Options:
+  --source <path>      SOURCE directory (required)
+  --prev <path>        PREV directory (required)
+  --pend <path>        PEND directory (required)
+  --deltas <path>      DELTAS directory (required)
+  --backend <name>     Delta backend: zstd (default), xdelta3
+  --config <file>      Load options from JSON config file (flags override)
+  --dry-run            Print what would happen, execute nothing
+  --help               Show this help
+`.trim();
+
+export function parseArgs(argv) {
+  const { values, positionals } = nodeParseArgs({
+    args: argv,
+    options: {
+      source:    { type: 'string' },
+      prev:      { type: 'string' },
+      pend:      { type: 'string' },
+      deltas:    { type: 'string' },
+      backend:   { type: 'string' },
+      config:    { type: 'string' },
+      'dry-run': { type: 'boolean', default: false },
+      help:      { type: 'boolean', default: false },
+    },
+    allowPositionals: true,
+  });
+
+  if (values.help) {
+    console.log(HELP);
+    process.exit(0);
+  }
+
+  const command = positionals[0];
+  if (!command) {
+    console.error('Error: command required (run, status)\n');
+    console.error(HELP);
+    process.exit(1);
+  }
+
+  return { ...values, command, dryRun: values['dry-run'] };
+}