artgraph-plan-coverage

## Purpose Runs `artgraph plan-coverage` to detect **implicit impacts**: REQs that the files (or `path:symbol` pairs) listed in `tasks.md` will touch via the artgraph graph, but which are never mentioned in `tasks.md` / `plan.md` / `spec.md`. These are the "I forgot existing requirement X also lives in this file" misses that `artgraph impact` (forward) and `artgraph check` (drift vs lock) cannot catch on their own. Complementary to `artgraph-impact`: that Skill answers "what does this edit touch?" — this Skill answers "of the things this plan touches, what did the human forget to write down?". ## Steps ### 1. Prerequisite check See [install-check](../_shared/install-check.md) for the standard pre-flight check. If artgraph is not installed, stop and invoke the `artgraph-setup` Skill instead. > `<PM-exec>` is the project's package runner: `npx` (npm), `pnpm exec`, `bunx`, or `deno run -A npm:artgraph/cli`. Substitute the one detected by `_shared/package-manager.md` (or written in `.artgraph.json#packageManager`). **Symbol-level entries** (`Files: src/auth.ts:validateToken`, or class-method grain `Files: src/auth.ts:Sample.methodA`) require `.artgraph.json` to be set to `"mode": "symbol"` and the graph re-scanned. See [Skills Guide — file vs symbol mode](../../../docs/skills-guide.md#file-mode-vs-symbol-mode) for trade-offs. ### 2. Pick a mode and run | Mode | Trigger | Command | | --- | --- | --- | | (a) Auto-detect spec | Spec Kit project (`SPECIFY_FEATURE_DIRECTORY` ...