Add rsync exit code awareness + plan operation abstraction

- spawn.js: rsync() wrapper handles exit codes 0/24 as OK, 23 as fatal
- spawn.js: capture() accepts allowedExitCodes option
- run.js: all rsync calls go through rsync() wrapper
- PLAN.md: document planned operation abstraction refactor

lib/commands/run.js

@@ -3,7 +3,7 @@
  */
 import { mkdir, writeFile } from 'fs/promises';
 import { join } from 'path';
-import { run as spawn, capture } from '../spawn.js';
+import { run as spawn, rsync } from '../spawn.js';
 import { parseItemize } from '../itemize.js';
 import { getBackend } from '../backends/index.js';
 import { readState, writeState, PHASES } from '../state.js';
@@ -33,28 +33,22 @@ export async function runCommand(config) {
   // ── Phase 2: rsync PREV → PEND (local seed, with delete) ────
   await setPhase(deltas, state, PHASES.RSYNC_LOCAL, dry);
   console.log('\n── rsync PREV → PEND (local seed) ──');
-  await spawn('rsync', ['-aP', '--delete', trailingSlash(prev), trailingSlash(pend)], { dryRun: dry });
+  await rsync(['-aP', '--delete', trailingSlash(prev), trailingSlash(pend)], { dryRun: dry });
 
   // ── Phase 3: rsync SOURCE → PEND, capture change list ───────
   await setPhase(deltas, state, PHASES.RSYNC_REMOTE, dry);
   console.log('\n── rsync SOURCE → PEND ──');
 
-  let changes = [];
+  const output = await rsync(
+    ['-aP', '--itemize-changes', '--delete', trailingSlash(source), trailingSlash(pend)],
+    { dryRun: dry, capture: true },
+  );
+  const changes = dry ? [] : parseItemize(output);
   if (!dry) {
-    const rsyncArgs = [
-      '-aP',
-      '--itemize-changes',
-      '--delete',
-      trailingSlash(source),
-      trailingSlash(pend),
-    ];
-    const output = await capture('rsync', rsyncArgs);
-    changes = parseItemize(output);
     console.log(`  ${changes.length} file(s) changed`);
     for (const c of changes) console.log(`  [${c.status}] ${c.path}`);
   } else {
-    console.log(`$ rsync -aP --itemize-changes --delete ${trailingSlash(source)} ${trailingSlash(pend)}`);
-    console.log('[dry-run] (change list will be determined at runtime)');
+    console.log('  [dry-run] change list determined at runtime');
   }
 
   // ── Phase 4: Generate per-file deltas into DELTAS/tmp/N/ ────
@@ -132,7 +126,7 @@ export async function runCommand(config) {
   // ── Phase 6: Promote PEND → PREV ────────────────────────────
   await setPhase(deltas, state, PHASES.PROMOTING, dry);
   console.log('\n── Promote PEND → PREV ──');
-  await spawn('rsync', ['-aP', '--delete', trailingSlash(pend), trailingSlash(prev)], { dryRun: dry });
+  await rsync(['-aP', '--delete', trailingSlash(pend), trailingSlash(prev)], { dryRun: dry });
 
   // ── Done ─────────────────────────────────────────────────────
   state.last_complete = seq;