Add rule: all software repos must have tests

Require at least minimal tests (e.g. import/compile check) using the
platform-standard test framework. make test must never be a no-op.

prompts/REPO_POLICIES.md

@@ -62,6 +62,12 @@ style conventions are in separate documents:
   `make lint && make fmt-check`. The Makefile should provide a `make hooks`
   target to install the pre-commit hook.
 
+- All repos with software must have tests that run via the platform-standard
+  test framework (`go test`, `pytest`, `jest`/`vitest`, etc.). If no meaningful
+  tests exist yet, add the most minimal test possible — e.g. importing the
+  module under test to verify it compiles/parses. There is no excuse for
+  `make test` to be a no-op.
+
 - `make test` must complete in under 20 seconds. Add a 30-second timeout in the
   Makefile.