goalforge-brieflisted

# goalforge-brief Author a single, immutable brief for one complexity-gated task so a cheaper executor tier can implement it without re-deriving the surrounding context. ## Visibility PRIVATE child of the `goalforge` package. Discovery is one level deep, so this nested SKILL is never a user-invocable front door. Its **only** call site is `goalforge-execute`'s pre-dispatch flow (wp-06/task-04), which invokes it once per gated task at the `pending → briefed` transition. ## Complexity gate (trigger condition) Author a brief **only** when the task's frontmatter field `complexity ∈ {medium, high}`. The gate reads the `complexity:` field directly from the target `task-NN.md` frontmatter — it does **NOT** call `goalforge-wp-complexity.sh` (that script computes a WP-level signal; this gate is a per-task read). - `complexity: low` → **skip** briefing entirely; the executor dispatches the task directly with no brief artifact. - `complexity: medium | high` → author exactly one `brief-<task-slug>.md` sibling (full task filename minus `.md` — `brief-task-NN-<slug>.md`, the name `execute/brief-staleness.sh` resolves; a bare `brief-task-NN.md` is invisible to it). Author once. A brief is **immutable** after authoring; re-authoring a task that already has a sibling `brief-<task-slug>.md` is a no-op (staleness handling is the executor's re-validation step, wp-06/task-04 — it records a re-brief request to the task checkpoint block, it never mutates the brief in place). ## Dispa