feat: add persistent vector build state helpers

paperforge/memory/vector_db.py

@@ -282,6 +282,58 @@ def retrieve_chunks(vault: Path, query: str, limit: int = 5, expand: bool = True
     return chunks
 
 
+# ── Persistent build state ─────────────────────────────────────────────────
+
+
+def get_vector_build_state_path(vault: Path) -> Path:
+    """Return path to vector-build-state.json."""
+    from paperforge.config import paperforge_paths
+    paths = paperforge_paths(vault)
+    index_dir = (paths.get("memory_db", paths.get("index", vault / "System" / "PaperForge"))).parent
+    return index_dir / "vector-build-state.json"
+
+
+def read_vector_build_state(vault: Path) -> dict:
+    """Read persisted build state. Returns default idle state if file missing."""
+    path = get_vector_build_state_path(vault)
+    if not path.exists():
+        return {
+            "status": "idle",
+            "current": 0,
+            "total": 0,
+            "paper_id": "",
+            "last_update": "",
+            "started_at": "",
+            "finished_at": "",
+            "resume_supported": True,
+            "mode": "local",
+            "model": "BAAI/bge-small-en-v1.5",
+            "message": "",
+            "pid": 0,
+        }
+    try:
+        return json.loads(path.read_text(encoding="utf-8"))
+    except Exception:
+        return {"status": "idle", "current": 0, "total": 0, "paper_id": ""}
+
+
+def write_vector_build_state(vault: Path, state: dict) -> None:
+    """Persist build state to disk atomically."""
+    path = get_vector_build_state_path(vault)
+    path.parent.mkdir(parents=True, exist_ok=True)
+    tmp = path.with_suffix(".tmp")
+    tmp.write_text(json.dumps(state, ensure_ascii=False, indent=2), encoding="utf-8")
+    tmp.replace(path)
+
+
+def mark_vector_build_state(vault: Path, **fields) -> dict:
+    """Update specific fields in the build state file. Returns updated state."""
+    state = read_vector_build_state(vault)
+    state.update(fields)
+    write_vector_build_state(vault, state)
+    return state
+
+
 def get_embed_status(vault: Path) -> dict:
     """Get vector DB status."""
     db_path = get_vector_db_path(vault)

tests/unit/memory/test_vector_db.py

@@ -0,0 +1,41 @@
+from __future__ import annotations
+
+from paperforge.memory.vector_db import (
+    get_vector_build_state_path,
+    read_vector_build_state,
+    write_vector_build_state,
+    mark_vector_build_state,
+)
+
+
+def test_vector_build_state_defaults_when_missing(tmp_path):
+    vault = tmp_path / "vault"
+    vault.mkdir()
+    state = read_vector_build_state(vault)
+    assert state["status"] == "idle"
+    assert state["current"] == 0
+
+
+def test_vector_build_state_roundtrip(tmp_path):
+    vault = tmp_path / "vault"
+    vault.mkdir()
+    original = {
+        "status": "running", "current": 5, "total": 20,
+        "paper_id": "ABC12345", "last_update": "now",
+        "started_at": "", "finished_at": "",
+        "resume_supported": True, "mode": "local",
+        "model": "bge-small", "message": "", "pid": 0,
+    }
+    write_vector_build_state(vault, original)
+    loaded = read_vector_build_state(vault)
+    assert loaded == original
+
+
+def test_mark_vector_build_state_updates_field(tmp_path):
+    vault = tmp_path / "vault"
+    vault.mkdir()
+    write_vector_build_state(vault, {"status": "idle", "current": 0, "total": 0})
+    mark_vector_build_state(vault, current=10, paper_id="XYZ")
+    state = read_vector_build_state(vault)
+    assert state["current"] == 10
+    assert state["paper_id"] == "XYZ"