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

project_manager.py

@@ -121,14 +121,59 @@ def default_project(name: str = "unnamed") -> dict:
 
 # ── load / save ──────────────────────────────────────────────────────────────
 
+def get_history_path(project_path: str | Path) -> Path:
+    p = Path(project_path)
+    return p.parent / f"{p.stem}_history.toml"
+
+
 def load_project(path) -> dict:
     with open(path, "rb") as f:
-        return tomllib.load(f)
+        proj = tomllib.load(f)
+    
+    # Automatic Migration: move legacy 'discussion' to sibling file
+    hist_path = get_history_path(path)
+    if "discussion" in proj:
+        disc = proj.pop("discussion")
+        # Save to history file if it doesn't exist yet (or overwrite to migrate)
+        with open(hist_path, "wb") as f:
+            tomli_w.dump(disc, f)
+        # Save the stripped project file
+        save_project(proj, path)
+        # Restore for the returned dict so GUI works as before
+        proj["discussion"] = disc
+    else:
+        # Load from sibling if it exists
+        if hist_path.exists():
+            proj["discussion"] = load_history(path)
+    
+    return proj
 
 
-def save_project(proj: dict, path):
+def load_history(project_path: str | Path) -> dict:
+    hist_path = get_history_path(project_path)
+    if hist_path.exists():
+        with open(hist_path, "rb") as f:
+            return tomllib.load(f)
+    return {}
+
+
+def save_project(proj: dict, path, disc_data: dict | None = None):
+    # Ensure 'discussion' is NOT in the main project dict
+    if "discussion" in proj:
+        # If disc_data wasn't provided, use the one from proj
+        if disc_data is None:
+            disc_data = proj["discussion"]
+        # Remove it so it doesn't get saved to the main file
+        proj = dict(proj) # shallow copy to avoid mutating caller's dict
+        del proj["discussion"]
+
     with open(path, "wb") as f:
         tomli_w.dump(proj, f)
+        
+    if disc_data:
+        hist_path = get_history_path(path)
+        with open(hist_path, "wb") as f:
+            tomli_w.dump(disc_data, f)
 
 
 # ── migration helper ─────────────────────────────────────────────────────────