move top-level modules into a real package

plans/09-domain-specific-cli-exceptions.md

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+# 9. Use Domain-Specific Exceptions Instead of Chroma Exceptions in CLI Mapping
+
+## Summary
+
+Hide Chroma-specific exceptions behind application-level exceptions so the CLI does not depend on Chroma's exception model.
+
+## Implementation Steps
+
+- Define app-level exceptions such as `CollectionNotFoundError`, `CollectionAlreadyExistsError`, and `StorageOperationError`.
+- Convert Chroma exceptions inside the repository layer.
+- Update CLI command error mappings to handle app-level exceptions only.
+- Preserve existing user-facing messages for missing and duplicate collections.
+- Avoid importing `chromadb.errors` in CLI modules after the repository layer owns that boundary.
+
+## Public Interface Changes
+
+- CLI behavior and messages should remain the same.
+- Internal error contracts change from Chroma exceptions to app-level exceptions.
+
+## Test Plan
+
+- Unit test repository exception translation.
+- Unit test CLI mappings for app-level exceptions.
+- Smoke test missing collection, duplicate collection, and successful operations.
+
+## Assumptions
+
+- Chroma remains the only storage backend for now.
+- The exception layer is still useful because it prevents storage details from leaking upward.