Add contract/test example to test plan template

.ai/templates/test-plan.md

@@ -26,6 +26,27 @@
 - [ ] Failure modes are covered.
 - [ ] Postconditions are observable.
 
+## Example
+
+Feature: Export a territory
+
+Contract under test:
+
+- Preconditions: The territory exists and the user is authorized.
+- Inputs: Territory ID.
+- Outputs: A downloadable ZIP file.
+- Postconditions: The ZIP contains the generated XLSX and PDFs.
+- Invariants: The exported files are named consistently.
+- Failure modes: Missing territory, file write failure, or export timeout.
+- Side effects: Temporary export files may be created and cleaned up after download.
+
+Test focus:
+
+- Verify the export is rejected when the territory is missing.
+- Verify the ZIP contains both the spreadsheet and the PDFs.
+- Verify failed file writes are reported as errors.
+- Verify cleanup happens after download.
+
 ---
 
 ## Self-Evolution Protocol