Refactor test cases for improved readability and consistency

- Updated test_dns.py to enhance mock function definitions and improve spacing for better readability.
- Modified test_filters.py to streamline assertions and ensure consistent formatting across test cases.
- Cleaned up test_import_export.py by organizing imports and ensuring consistent formatting in CSV and JSON tests.
- Improved test_main.py by refining mock setups and ensuring consistent error handling in assertions.

docs/agents/domain.md

@@ -0,0 +1,36 @@
+# Domain Docs
+
+How engineering skills should consume this repository's domain documentation
+when exploring the codebase.
+
+## Before exploring, read these
+
+- **`CONTEXT.md`** at the repository root.
+- **`docs/adr/`** — read ADRs that affect the area about to be changed.
+
+If either location does not exist, proceed silently. The `/domain-modeling`
+skill creates domain documentation when terminology or decisions are resolved.
+
+## File structure
+
+This repository uses a single-context layout:
+
+/
+├── CONTEXT.md
+├── docs/
+│   └── adr/
+└── src/
+
+## Use the glossary's vocabulary
+
+When output names a domain concept—for example in an issue title, refactor
+proposal, hypothesis, or test name—use the term defined in `CONTEXT.md`. Avoid
+synonyms that the glossary explicitly rejects.
+
+If a required concept is missing, reconsider whether the proposed language
+belongs to the project or note the gap for `/domain-modeling`.
+
+## Flag ADR conflicts
+
+Explicitly surface output that contradicts an existing ADR instead of silently
+overriding it.