Add focused changed-path test wrapper

docs/Architecture/Testing Policy.md

@@ -13,6 +13,21 @@ This repository tests its configuration at defined seams. The tests run with `ba
 | Script syntax | `tests/scripts_syntax.bats` | `bash -n` clean, executable bits, shellcheck when available |
 | Deployment flow | `tests/deployment_flow.bats` | deploy.sh exists, targets known, SSH reachable (skips offline) |
 
+## Focused pre-commit testing
+
+For normal commits, use the focused wrapper:
+
+```bash
+./scripts/test-changed.sh
+```
+
+It reads staged paths with `git diff --cached` and runs only the mapped Bats
+files. Use `--list` to inspect the selection without running tests, or
+`--paths FILE ...` to preview a mapping. Shared test infrastructure and
+unmapped paths fail closed rather than silently skipping coverage. Run the
+full suite with `./tests/run.sh` when changing shared test helpers, the test
+runner, or when focused coverage is not sufficient.
+
 ## Red-Green
 
 Tests are written first. A failing test means the seam is not satisfied; the config change that makes it pass is the only acceptable fix. No `--no-verify`, no deleting tests without approval.