feat(project): Segregate discussion history into sibling TOML file

tests/test_history_migration.py

@@ -0,0 +1,56 @@
+import pytest
+import tomli_w
+import tomllib
+from pathlib import Path
+from project_manager import load_project, save_project, default_project
+
+def test_migration_on_load(tmp_path):
+    # Setup legacy project file with discussion
+    proj_path = tmp_path / "manual_slop.toml"
+    hist_path = tmp_path / "manual_slop_history.toml"
+    
+    legacy_data = default_project("test-project")
+    legacy_data["discussion"]["discussions"]["main"]["history"] = ["Hello", "World"]
+    
+    with open(proj_path, "wb") as f:
+        tomli_w.dump(legacy_data, f)
+        
+    # Load project - should trigger migration
+    loaded_data = load_project(proj_path)
+    
+    # Assertions
+    assert "discussion" in loaded_data
+    assert loaded_data["discussion"]["discussions"]["main"]["history"] == ["Hello", "World"]
+    
+    # Check that it's NOT in the main file on disk anymore
+    with open(proj_path, "rb") as f:
+        on_disk = tomllib.load(f)
+    assert "discussion" not in on_disk
+    
+    # Check history file
+    assert hist_path.exists()
+    with open(hist_path, "rb") as f:
+        hist_data = tomllib.load(f)
+    assert hist_data["discussions"]["main"]["history"] == ["Hello", "World"]
+
+def test_save_separation(tmp_path):
+    # Setup fresh project data
+    proj_path = tmp_path / "manual_slop.toml"
+    hist_path = tmp_path / "manual_slop_history.toml"
+    
+    proj_data = default_project("test-project")
+    proj_data["discussion"]["discussions"]["main"]["history"] = ["Saved", "Separately"]
+    
+    # Save project - should save both files
+    save_project(proj_data, proj_path)
+    
+    assert proj_path.exists()
+    assert hist_path.exists()
+    
+    with open(proj_path, "rb") as f:
+        p = tomllib.load(f)
+    assert "discussion" not in p
+    
+    with open(hist_path, "rb") as f:
+        h = tomllib.load(f)
+    assert h["discussions"]["main"]["history"] == ["Saved", "Separately"]