The coach enforces a strict validation contract by requiring an exact substring membership check on every proposed edit, dropping any replacement whose target text cannot be found verbatim in the draft while attaching occurrence tracking to prevent corrupting multiple matching spans.

sequenceDiagram
    participant LLM as Coach Model
    participant Val as Validation Layer
    participant Draft as Original Draft
    LLM->>Val: Propose {original, replacement}
    Val->>Draft: Verify "original in text"
    alt String Found Exactly
        Draft-->>Val: Match count (occurrences)
        Val-->>Draft: Stage verbatim replacement
    else String Mismatch / Hallucination
        Val-->>Val: Drop proposed edit
    end