artgraph-impact

## Purpose Runs `artgraph impact` to compute **forward propagation from one or more source files or specific exported symbols**: which requirements, docs, and other files a proposed edit touches. The CLI accepts file paths and `path:symbol` pairs — REQ-IDs and `doc:` prefixes are rejected. Use the output to make an edit with explicit awareness of its affected scope and drift. For detecting the **inverse** — REQs that are implicitly affected by files listed in `tasks.md` but never mentioned in spec/plan/tasks — and for any tasks.md / plan.md driven analysis, use `artgraph-plan-coverage` instead. ## Input modes Pick one based on what the user supplied: | Mode | Trigger | Command | | --- | --- | --- | | (a) Diff | `git status` shows staged or unstaged changes | `<PM-exec> impact --diff --format json` | | (b) Explicit file or symbol source | User named file paths or `path:symbol` pairs | `<PM-exec> impact <file_or_symbol...>` | | (c) Ask | Neither — no diff, no file paths | Ask: "Which file(s) or `path:symbol` pair should I analyze?" then re-enter with mode (b) | Add `--tests` to mode (a) (`<PM-exec> impact --diff --tests --format json`, spec 020 FR-018) when the user wants to know **which tests to re-run** after the change, instead of just which REQs are touched — it lists the tagged tests of REQs that exclusively exercise a changed symbol (`testsToRun`), so you can run only those instead of the whole suite. It requires a trace: with zero trace shards it exits 1 with insta...