fix: repair pgvector migration to actually convert embedding column from text to vector(1536)

The original migration used a fragile add-copy-drop-rename pattern with
_jsonb casts that silently failed, leaving the embedding column as text.
Replace with a direct ALTER COLUMN TYPE ... USING embedding::vector(1536)
that is fully idempotent and handles all partial states from previous
failed attempts.

memento-note/prisma/migrations/20260512120000_pgvector_and_fts_search/migration.sql

@@ -1,48 +1,43 @@
 -- Phase 1: Enable pgvector extension
 CREATE EXTENSION IF NOT EXISTS vector;
 
--- Phase 2: Convert embedding column from text/JSON to vector(1536) if needed
+-- Phase 2: Convert embedding column from text to vector(1536)
+-- Idempotent: detects current column type and only converts when needed.
+-- Handles all partial states from previous failed migration attempts:
+--   A) embedding is text → direct ALTER COLUMN TYPE conversion
+--   B) embedding already vector → skip
+--   C) embedding missing, _vec_tmp exists → rename
 DO $$
 DECLARE
-    _udt text;
-    _vec_tmp_exists boolean;
+    _emb_type text;
+    _tmp_type text;
 BEGIN
-    SELECT udt_name INTO _udt
+    SELECT udt_name INTO _emb_type
     FROM information_schema.columns
     WHERE table_schema = 'public'
       AND table_name = 'NoteEmbedding'
       AND column_name = 'embedding';
 
-    IF _udt IS NOT NULL AND _udt != 'vector' THEN
-        SELECT EXISTS (
-            SELECT 1 FROM information_schema.columns
-            WHERE table_schema = 'public'
-              AND table_name = 'NoteEmbedding'
-              AND column_name = '_vec_tmp'
-        ) INTO _vec_tmp_exists;
+    IF _emb_type = 'vector' THEN
+        RETURN;
+    END IF;
 
-        IF NOT _vec_tmp_exists THEN
-            ALTER TABLE "NoteEmbedding" ADD COLUMN "_vec_tmp" vector(1536);
-        END IF;
+    IF _emb_type IS NOT NULL THEN
+        ALTER TABLE "NoteEmbedding" DROP COLUMN IF EXISTS "_vec_tmp";
+        ALTER TABLE "NoteEmbedding"
+            ALTER COLUMN "embedding" TYPE vector(1536)
+            USING "embedding"::vector(1536);
+        RETURN;
+    END IF;
 
-        UPDATE "NoteEmbedding"
-        SET "_vec_tmp" = ("embedding"::jsonb)::text::vector(1536)
-        WHERE "embedding" IS NOT NULL
-          AND "_vec_tmp" IS NULL;
+    SELECT udt_name INTO _tmp_type
+    FROM information_schema.columns
+    WHERE table_schema = 'public'
+      AND table_name = 'NoteEmbedding'
+      AND column_name = '_vec_tmp';
 
-        ALTER TABLE "NoteEmbedding" DROP COLUMN "embedding";
+    IF _tmp_type IS NOT NULL THEN
         ALTER TABLE "NoteEmbedding" RENAME COLUMN "_vec_tmp" TO "embedding";
-    ELSIF _udt IS NULL THEN
-        SELECT EXISTS (
-            SELECT 1 FROM information_schema.columns
-            WHERE table_schema = 'public'
-              AND table_name = 'NoteEmbedding'
-              AND column_name = '_vec_tmp'
-        ) INTO _vec_tmp_exists;
-
-        IF _vec_tmp_exists THEN
-            ALTER TABLE "NoteEmbedding" RENAME COLUMN "_vec_tmp" TO "embedding";
-        END IF;
     END IF;
 END $$;