story-kit: create 171_story_persist_test_results_to_story_files

.story_kit/work/1_upcoming/171_story_persist_test_results_to_story_files.md

@@ -14,6 +14,7 @@ As a project owner, I want test results written to the story markdown file when
 - [ ] Test results section shows test name, status (pass/fail), and details for each recorded test
 - [ ] Results persist across server restarts by being read back from the file on load
 - [ ] ensure_acceptance reads from the persisted file data, not just in-memory state
+- [ ] When a coder agent starts on a story, snapshot the current overall test coverage (from cargo llvm-cov) and write it as front matter (e.g. `coverage_baseline: 42.3%`) so coverage delta can be computed later
 
 ## Out of Scope