Replaces single-path cf-orch allocation with a three-tier strategy:
tier 1 task_allocate() (coordinator-driven), tier 2 direct CFOrchClient.allocate()
(TaskNotRegistered fallback), tier 3 local LLMRouter. Module-level imports for
CFOrchClient and LLMRouter make all three paths patchable in tests without
import caching issues.
- upsert_slot: raise 422 immediately if meal_type not in VALID_MEAL_TYPES
- update_prep_task: assert whitelist safety contract after dict comprehension
- CreatePlanRequest: week_start typed as date with must_be_monday validator; str() cast at call site
- PrepTask: frozen=True; build_prep_tasks rewired to use (priority, kwargs) tuples so frozen instances are built with correct sequence_order in one pass (no post-construction mutation)
- Move deferred import json to file-level in meal_plans.py
- Fix test dates: "2026-04-14" was a Tuesday; updated request bodies to "2026-04-13" (Monday)
