From baa6c758f54d9f653e791ef222fa2272a8683b4e Mon Sep 17 00:00:00 2001
From: Research Assistant <research@example.com>
Date: Mon, 18 May 2026 22:18:23 +0800
Subject: [PATCH] fix(vector): get_collection no longer silently deletes
 collection on error; memory builder skips full rebuild when index hash
 matches

---
 paperforge/embedding/_chroma.py | 15 ++++-----------
 paperforge/memory/builder.py    | 21 +++++++++++++++++++--
 2 files changed, 23 insertions(+), 13 deletions(-)

diff --git a/paperforge/embedding/_chroma.py b/paperforge/embedding/_chroma.py
index ccf68832..3cdec382 100644
--- a/paperforge/embedding/_chroma.py
+++ b/paperforge/embedding/_chroma.py
@@ -22,17 +22,10 @@ def get_collection(vault: Path):
     db_path = get_vector_db_path(vault)
     db_path.mkdir(parents=True, exist_ok=True)
     client = chroma.PersistentClient(path=str(db_path))
-    try:
-        return client.get_or_create_collection(
-            name="paperforge_fulltext",
-            metadata={"hnsw:space": "cosine"},
-        )
-    except Exception:
-        client.delete_collection("paperforge_fulltext")
-        return client.create_collection(
-            name="paperforge_fulltext",
-            metadata={"hnsw:space": "cosine"},
-        )
+    return client.get_or_create_collection(
+        name="paperforge_fulltext",
+        metadata={"hnsw:space": "cosine"},
+    )
 
 
 def delete_paper_vectors(vault: Path, zotero_key: str) -> int:
diff --git a/paperforge/memory/builder.py b/paperforge/memory/builder.py
index d97580df..3367964e 100644
--- a/paperforge/memory/builder.py
+++ b/paperforge/memory/builder.py
@@ -129,7 +129,7 @@ def _import_correction_log(conn, vault: Path) -> int:
 
 def build_from_index(vault: Path) -> dict:
     """Read formal-library.json and build/rebuild paperforge.db.
-    
+
     Returns a dict with counts for reporting.
     """
     envelope = read_index(vault)
@@ -137,7 +137,6 @@ def build_from_index(vault: Path) -> dict:
         raise FileNotFoundError(
             "Canonical index not found. Run paperforge sync --rebuild-index."
         )
-    # Legacy format: bare list of entries (pre-envelope)
     if isinstance(envelope, list):
         items = envelope
         generated_at = ""
@@ -147,6 +146,24 @@ def build_from_index(vault: Path) -> dict:
     canonical_hash = compute_hash(items) if isinstance(items, list) and items and isinstance(items[0], dict) else ""
 
     db_path = get_memory_db_path(vault)
+    # fast-path: if index hash matches, nothing changed
+    if canonical_hash and db_path.exists():
+        try:
+            conn = get_connection(db_path, read_only=False)
+            cached = conn.execute("SELECT value FROM meta WHERE key='canonical_index_hash'").fetchone()
+            stored_version = get_schema_version(conn)
+            if cached and cached[0] == canonical_hash and stored_version == CURRENT_SCHEMA_VERSION:
+                papers_count = conn.execute("SELECT COUNT(*) FROM papers").fetchone()[0]
+                conn.close()
+                return {
+                    "papers_indexed": papers_count,
+                    "db_path": str(db_path),
+                    "hash_match": True,
+                }
+            conn.close()
+        except Exception:
+            pass
+
     conn = get_connection(db_path, read_only=False)
     try:
         stored_version = get_schema_version(conn)