feat(prompts): implement Phase 6 - Incremental Execution (FR-7, FR-8)

Add change detection, structural diff-based impact analysis,
configurable-depth incremental recomputation with circular suppression,
and impact debt tracking.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/unit/prompts/test_change_detector.py

@@ -0,0 +1,166 @@
+"""
+Unit tests for ChangeDetector.
+
+Tests change detection, recording, change types, and no-change cases.
+"""
+
+import pytest
+import tempfile
+from pathlib import Path
+
+from markitect.prompts.models import Artifact, ArtifactType, calculate_content_digest
+from markitect.prompts.incremental.detector import ChangeDetector
+from markitect.prompts.incremental.models import ChangeType
+
+
+@pytest.fixture
+def temp_db():
+    """Create temporary database for testing."""
+    with tempfile.NamedTemporaryFile(suffix=".db", delete=False) as f:
+        db_path = f.name
+    yield db_path
+    Path(db_path).unlink(missing_ok=True)
+
+
+@pytest.fixture
+def detector(temp_db):
+    """Create ChangeDetector instance."""
+    return ChangeDetector(temp_db)
+
+
+def _make_artifact(content="original content"):
+    """Helper to create an in-memory artifact."""
+    return Artifact.create(
+        space_id="space-1",
+        name="test-artifact",
+        content=content,
+        artifact_type=ArtifactType.CONTENT,
+    )
+
+
+class TestDetectChange:
+    """Tests for detecting content changes."""
+
+    def test_detect_modification(self, detector):
+        """Test detecting a content modification."""
+        artifact = _make_artifact("original content")
+        change = detector.detect_change(artifact, "modified content")
+
+        assert change is not None
+        assert change.artifact_id == artifact.id
+        assert change.old_digest == artifact.content_digest
+        assert change.new_digest == calculate_content_digest("modified content")
+        assert change.change_type == ChangeType.MODIFIED
+
+    def test_no_change_returns_none(self, detector):
+        """Test that identical content returns None."""
+        artifact = _make_artifact("same content")
+        change = detector.detect_change(artifact, "same content")
+
+        assert change is None
+
+    def test_detect_whitespace_change(self, detector):
+        """Test detecting whitespace-only changes."""
+        artifact = _make_artifact("content")
+        change = detector.detect_change(artifact, "content ")
+
+        assert change is not None
+        assert change.change_type == ChangeType.MODIFIED
+
+    def test_detect_empty_to_content(self, detector):
+        """Test detecting change from empty to content."""
+        artifact = _make_artifact("")
+        change = detector.detect_change(artifact, "new content")
+
+        assert change is not None
+        assert change.change_type == ChangeType.MODIFIED
+
+
+class TestDetectCreation:
+    """Tests for recording artifact creation."""
+
+    def test_detect_creation(self, detector):
+        """Test creation change record."""
+        change = detector.detect_creation("artifact-123", "new content")
+
+        assert change.artifact_id == "artifact-123"
+        assert change.old_digest is None
+        assert change.new_digest == calculate_content_digest("new content")
+        assert change.change_type == ChangeType.CREATED
+
+    def test_creation_has_unique_id(self, detector):
+        """Test that each creation gets a unique ID."""
+        change1 = detector.detect_creation("art-1", "content")
+        change2 = detector.detect_creation("art-2", "content")
+
+        assert change1.id != change2.id
+
+
+class TestDetectDeletion:
+    """Tests for recording artifact deletion."""
+
+    def test_detect_deletion(self, detector):
+        """Test deletion change record."""
+        artifact = _make_artifact("content to delete")
+        change = detector.detect_deletion(artifact)
+
+        assert change.artifact_id == artifact.id
+        assert change.old_digest == artifact.content_digest
+        assert change.change_type == ChangeType.DELETED
+
+
+class TestRecordChange:
+    """Tests for persisting change records."""
+
+    def test_record_and_retrieve(self, detector):
+        """Test recording a change and retrieving it."""
+        artifact = _make_artifact("original")
+        change = detector.detect_change(artifact, "modified")
+        assert change is not None
+
+        detector.record_change(change)
+        changes = detector.get_changes_for_artifact(artifact.id)
+
+        assert len(changes) == 1
+        assert changes[0].id == change.id
+        assert changes[0].artifact_id == artifact.id
+        assert changes[0].change_type == ChangeType.MODIFIED
+
+    def test_record_multiple_changes(self, detector):
+        """Test recording multiple changes for same artifact."""
+        artifact = _make_artifact("v1")
+
+        change1 = detector.detect_change(artifact, "v2")
+        detector.record_change(change1)
+
+        # Simulate artifact update
+        artifact.update_content("v2")
+        change2 = detector.detect_change(artifact, "v3")
+        detector.record_change(change2)
+
+        changes = detector.get_changes_for_artifact(artifact.id)
+        assert len(changes) == 2
+
+    def test_get_changes_by_type(self, detector):
+        """Test filtering changes by type."""
+        # Record a creation
+        creation = detector.detect_creation("art-new", "content")
+        detector.record_change(creation)
+
+        # Record a modification
+        artifact = _make_artifact("old")
+        modification = detector.detect_change(artifact, "new")
+        detector.record_change(modification)
+
+        created_changes = detector.get_changes_by_type(ChangeType.CREATED)
+        assert len(created_changes) == 1
+        assert created_changes[0].change_type == ChangeType.CREATED
+
+        modified_changes = detector.get_changes_by_type(ChangeType.MODIFIED)
+        assert len(modified_changes) == 1
+        assert modified_changes[0].change_type == ChangeType.MODIFIED
+
+    def test_no_changes_returns_empty(self, detector):
+        """Test querying changes for artifact with none recorded."""
+        changes = detector.get_changes_for_artifact("nonexistent")
+        assert changes == []