feat(ms-ai-architect): C2.3 onboarding skriver scheduled_detection cadence+enabled via gated CLI (TDD) [skip-docs]

K5 oppfylt: onboarding skriver scheduled_detection-blokka (enabled +
os_scheduler_cadence) til bruker-eid config; parseScheduleConfig leser den
tilbake til samme verdier (round-trip bevist deterministisk).

- serializeScheduleConfig(config) i detection-schedule.mjs — invers av
  parseScheduleConfig, rett ved parseren (én formatsannhet).
- write-schedule-config.mjs (NY, gated CLI, Claude-fri): merger på eksisterende
  config (override kun de to onboarding-eide nøklene; interval_days/
  include_skill_lifecycle overlever). backupFile + atomicWriteSync — ingen rå
  fs-write.
- backupFile(filePath, backupRoot) i lib/backup.mjs — presis enkeltfil-backup.
- onboard.md (orkestrator): «Planlagt deteksjon»-seksjon + scheduler i --status.
  onboarding-agent.md: note om at scheduler er orkestratorens jobb (ingen Bash).
- Avvik fra plan-tekst (dokumentert): scheduler-spørsmål i orkestrator, ikke agent.

Verifisert: detection-schedule 33/33 (+10) · backup-restore 15/15 (+3) ·
kb-update 213 · kb-eval 100 · validate 239/0/0 · test-hooks 11/11 ·
kb-integrity 192/192 · discovery 13/13 · gitleaks 3 pre-eksisterende.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

scripts/kb-update/lib/detection-schedule.mjs

@@ -88,6 +88,41 @@ export function parseScheduleConfig(text) {
   return cfg;
 }
 
+/**
+ * Serialize a schedule config to a full config-file text: a `---`-fenced
+ * frontmatter with the `scheduled_detection:` block (all four known keys) plus a
+ * short human header. The inverse of parseScheduleConfig — C2.3's onboarding
+ * write-path uses THIS (no second format definition): values are normalized
+ * exactly as coerce() would read them, so
+ *   parseScheduleConfig(serializeScheduleConfig(c))
+ * yields a DEFAULT-merged, normalized c (round-trip, acceptance K5). Pure.
+ * @param {Partial<typeof DEFAULT_SCHEDULE_CONFIG>} [config]
+ * @returns {string}
+ */
+export function serializeScheduleConfig(config = {}) {
+  const c = { ...DEFAULT_SCHEDULE_CONFIG, ...config };
+  const interval =
+    Number.isInteger(c.interval_days) && c.interval_days > 0
+      ? c.interval_days
+      : DEFAULT_SCHEDULE_CONFIG.interval_days;
+  return [
+    '---',
+    'scheduled_detection:',
+    `  enabled: ${c.enabled === true}`,
+    `  interval_days: ${interval}`,
+    `  include_skill_lifecycle: ${c.include_skill_lifecycle !== false}`,
+    `  os_scheduler_cadence: ${c.os_scheduler_cadence === 'interval' ? 'interval' : 'daily'}`,
+    '---',
+    '',
+    '# ms-ai-architect — planlagt deteksjon',
+    '',
+    'Skrevet av `/architect:onboard`. Styrer den opt-in, Claude-frie deteksjonen',
+    '(poll → rapport → discovery → skill-livssyklus). Endre `scheduled_detection`-',
+    'blokka over, eller kjør `/architect:onboard` på nytt.',
+    '',
+  ].join('\n');
+}
+
 /**
  * Load the opt-in schedule config. C2.1: the user-owned path
  * (~/.claude/ms-ai-architect/ms-ai-architect.local.md) takes precedence so the