feat: add ClassifiedAd domain entity

.agent/current-plan.md

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+# Plan: ClassifiedAd Domain Entity
+
+## Status: COMPLETED
+
+## Objective
+Create the first Domain Entity representing a ClassifiedAd with the specified attributes.
+
+## Decisions Made
+- **Location**: `domain/marketplace/classified_ad.py`
+- **Class style**: `@dataclass(frozen=True)` for immutability
+- **Validation**: No validation, just hold data
+- **Tests**: Yes, create unit tests
+
+## Entity Structure
+```python
+@dataclass(frozen=True)
+class ClassifiedAd:
+    id: UUID
+    _ownerId: UUID
+    title: str
+    text: str
+    _price: Decimal
+```
+
+## Files Created
+- `domain/__init__.py`
+- `domain/marketplace/__init__.py`
+- `domain/marketplace/classified_ad.py`
+- `tests/test_classified_ad.py`
+- `pyproject.toml`
+
+## Test Results
+- `test_classified_ad_creation` - PASSED
+- `test_classified_ad_is_immutable` - PASSED
+- `test_classified_ad_equality` - PASSED

.gitignore

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+env/
+__pycache__/
+*.pyc
+.pytest_cache/
+*.egg-info/

AGENTS.md

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+# AGENTS.md
+
+## Project Context
+
+This is a training project to learn functional programming in Python. Both Python and functional programming are relatively new. The learning approach uses an example project based on "Hands-on Domain Driven Design with .NET Core".
+
+## Collaboration Principles
+
+### Communication Style
+- Be honest and objective. Evaluate all suggestions, ideas, and feedback on their technical merits.
+- Do not be overly complementary or sycophantic.
+- If something does not align with best practices or could be improved, say so directly and constructively.
+- Technical accuracy and project quality take precedence over being agreeable.
+
+### Command and Code Style
+- Prefer simple commands over complex ones.
+- Default to simple, single-purpose commands.
+- Avoid one-liners that sacrifice clarity for brevity.
+
+### Workflow
+- We build production code together.
+- User handles implementation details; AI guides architecture and catches complexity early.
+- Challenge assumptions and ideas when it's useful. Be critical, not agreeable.
+
+## Core Workflow: Research → Plan → Implement → Validate
+Start every feature with: "Let me research the codebase and create a plan before implementing."
+
+Research - Understand existing patterns and architecture
+Plan - Propose approach and verify with you
+Implement - Build with tests and error handling
+Validate - ALWAYS run formatters, linters, and tests after implementation
+Whenever working on a feature or issue, let's always come up with a plan first, then save it to a file called /.agent/current-plan.md, before getting started with code changes. Update this file as the work progresses.
+Let's use pure functions where possible to improve readability and testing.

domain/__init__.py

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+from .marketplace import classified_ad

domain/marketplace/__init__.py

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+from .classified_ad import ClassifiedAd

domain/marketplace/classified_ad.py

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+from dataclasses import dataclass
+from decimal import Decimal
+from uuid import UUID
+
+
+@dataclass(frozen=True)
+class ClassifiedAd:
+    id: UUID
+    _ownerId: UUID
+    title: str
+    text: str
+    _price: Decimal

pyproject.toml

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+[build-system]
+requires = ["setuptools"]
+build-backend = "setuptools.backends._legacy:_Backend"
+
+[project]
+name = "python-fun"
+version = "0.1.0"
+requires-python = ">=3.12"
+
+[tool.pytest.ini_options]
+pythonpath = ["."]

tests/test_classified_ad.py

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+from decimal import Decimal
+from uuid import UUID, uuid4
+
+from domain.marketplace.classified_ad import ClassifiedAd
+
+
+def test_classified_ad_creation():
+    ad_id = uuid4()
+    owner_id = uuid4()
+
+    ad = ClassifiedAd(
+        id=ad_id,
+        _ownerId=owner_id,
+        title="Test Title",
+        text="Test text content",
+        _price=Decimal("99.99"),
+    )
+
+    assert ad.id == ad_id
+    assert ad._ownerId == owner_id
+    assert ad.title == "Test Title"
+    assert ad.text == "Test text content"
+    assert ad._price == Decimal("99.99")
+
+
+def test_classified_ad_is_immutable():
+    ad = ClassifiedAd(
+        id=uuid4(),
+        _ownerId=uuid4(),
+        title="Title",
+        text="Text",
+        _price=Decimal("10.00"),
+    )
+
+    try:
+        ad.title = "New Title"  # type: ignore
+        assert False, "Should have raised FrozenInstanceError"
+    except AttributeError:
+        pass
+
+
+def test_classified_ad_equality():
+    ad_id = uuid4()
+    owner_id = uuid4()
+
+    ad1 = ClassifiedAd(
+        id=ad_id,
+        _ownerId=owner_id,
+        title="Title",
+        text="Text",
+        _price=Decimal("10.00"),
+    )
+    ad2 = ClassifiedAd(
+        id=ad_id,
+        _ownerId=owner_id,
+        title="Title",
+        text="Text",
+        _price=Decimal("10.00"),
+    )
+
+    assert ad1 == ad2