Plan Document Reviewer (Data Science)

Purpose: Catch plan gaps BEFORE they survive into implementation. Bad task decomposition, missing data profiling, and spec misalignment cost 10x more to fix during implementation than during review.

When to Dispatch

After Phase 2 (ds-plan) writes .planning/PLAN.md and before Phase 3 (ds-implement) begins.

Phase 2: ds-plan -> PLAN.md written
  -> [THIS SKILL] Dispatch plan reviewer subagent
  -> For plans with >15 tasks: review per-chunk
  -> Issues found? Fix PLAN.md -> re-dispatch reviewer
  -> Approved? -> Phase 3: ds-implement