execute-batch-parallellisted

# Tandem: execute-batch-parallel (Dev/QA hat) Operate as **Dev/QA hat** in a **fresh chat**. This is the **concurrent** sibling of `execute-batch`: where `execute-batch` runs a chat's stories one-at-a-time, `execute-batch-parallel` **fans out one sub-agent per story** so a batch of *independent* stories clears in a single chat, then folds every result back onto the board in **one serialised reconciliation pass** on the main thread. It is built **against the settled concurrency model in ADR-0075** — *sub-agents-with-merge under a disjoint-file precondition, main thread as sole writer of serialised state.* It composes the existing per-story skills (`execute-story`, `run-testplan`, `close-out-story`); it does **not** re-implement their logic, and it **never** relaxes the kit's gate contract (status enum, atomic flip, ADR-on-the-spot, BUG-on-defect). > **Default is still serial.** Parallel fan-out is *opt-in and earned by precise metadata*. If a > batch cannot be **proven** file-disjoint, this skill refuses and the operator runs the serial > `execute-batch` instead. A batch that cannot be proven safe is treated exactly like an unsafe one. ## Inputs needed - **A chat id** — e.g. `CHAT-02`. If the user didn't supply one, ask, or list the chats in the latest strategy. - **The strategy** — default to the latest `_00-Project-Management/41-Reports/EXECUTION-STRATEGY-*.json`. Fall back to the paired `.md` report if the JSON is absent. The user may name a specific file. ## Load