Add E2E tests, fix bugs

Made-with: Cursor

_docs/02_document/modules/credentials.md

@@ -0,0 +1,55 @@
+# Module: credentials
+
+## Purpose
+
+Simple data holder for user authentication credentials (email + password).
+
+## Public Interface
+
+### Classes
+
+#### `Credentials` (cdef class)
+
+| Attribute | Type | Visibility |
+|-----------|------|------------|
+| email     | str  | public     |
+| password  | str  | public     |
+
+| Method         | Signature                                    | Description                        |
+|----------------|----------------------------------------------|------------------------------------|
+| `__init__`     | `(self, str email, str password)`            | Constructor                        |
+| `__str__`      | `(self) -> str`                              | Returns `"email: password"` format |
+
+## Internal Logic
+
+No logic — pure data class.
+
+## Dependencies
+
+- **Internal**: none (leaf module)
+- **External**: none
+
+## Consumers
+
+- `security` — `get_api_encryption_key` takes `Credentials` as parameter
+- `api_client` — holds a `Credentials` instance, uses `.email` and `.password` for login and key derivation
+
+## Data Models
+
+The `Credentials` class itself is the data model.
+
+## Configuration
+
+None.
+
+## External Integrations
+
+None.
+
+## Security
+
+Stores plaintext password in memory. No encryption at rest.
+
+## Tests
+
+No tests found.