diff --git a/src/db/postgres/index.ts b/src/db/postgres/index.ts
index 5df699c..1b639f6 100644
--- a/src/db/postgres/index.ts
+++ b/src/db/postgres/index.ts
@@ -465,14 +465,30 @@ export class PostgresKnowledgeDB implements IKnowledgeStore {
 			this.pgvectorReady = false;
 			return;
 		}
+		// Check whether the HNSW index already exists. CREATE INDEX IF NOT EXISTS
+		// still requires table ownership, so it can fail with "must be owner of
+		// table" on managed Postgres where the schema was bootstrapped by a
+		// different role (e.g. Cloud SQL with a separate admin user). When the
+		// index is already there from a prior run, treat that as success and
+		// keep ANN enabled instead of degrading to Path B.
+		const hnswExists = await this.sql`
+			SELECT 1 FROM pg_class c
+			JOIN pg_namespace n ON n.oid = c.relnamespace
+			WHERE c.relkind = 'i'
+			  AND n.nspname = current_schema()
+			  AND c.relname = 'idx_entry_embedding_halfvec_hnsw'
+		`;
+
 		try {
 			await this.sql`DROP INDEX IF EXISTS idx_entry_embedding_vec_hnsw`;
-			await this.sql.unsafe(`
-				CREATE INDEX IF NOT EXISTS idx_entry_embedding_halfvec_hnsw
-				ON knowledge_entry
-				USING hnsw ((embedding_vec::halfvec(${dims})) halfvec_cosine_ops)
-				WITH (m = 16, ef_construction = 64)
-			`);
+			if (hnswExists.length === 0) {
+				await this.sql.unsafe(`
+					CREATE INDEX IF NOT EXISTS idx_entry_embedding_halfvec_hnsw
+					ON knowledge_entry
+					USING hnsw ((embedding_vec::halfvec(${dims})) halfvec_cosine_ops)
+					WITH (m = 16, ef_construction = 64)
+				`);
+			}
 		} catch (err) {
 			logger.warn(
 				`[pg-db] ANN index creation failed — ANN search disabled. Will retry on next startup. Error: ${err instanceof Error ? err.message : String(err)}`,
diff --git a/src/db/postgres/migrations.ts b/src/db/postgres/migrations.ts
index 7a834a9..696655b 100644
--- a/src/db/postgres/migrations.ts
+++ b/src/db/postgres/migrations.ts
@@ -514,17 +514,31 @@ export const PG_MIGRATIONS: Array<{
 			// Replace legacy vector HNSW index with halfvec ANN index when supported.
 			await sql`DROP INDEX IF EXISTS idx_entry_embedding_vec_hnsw`;
 			if (dims <= 4000) {
-				try {
-					await sql.unsafe(`
-						CREATE INDEX IF NOT EXISTS idx_entry_embedding_halfvec_hnsw
-						ON knowledge_entry
-						USING hnsw ((embedding_vec::halfvec(${dims})) halfvec_cosine_ops)
-						WITH (m = 16, ef_construction = 64)
-					`);
-				} catch (err) {
-					logger.warn(
-						`[pg-db] Migration v17: ANN index creation skipped. ANN search disabled for this store. Error: ${err instanceof Error ? err.message : String(err)}`,
-					);
+				// Skip CREATE INDEX if the halfvec HNSW index is already present.
+				// CREATE INDEX IF NOT EXISTS still requires table ownership and
+				// fails with "must be owner of table" on managed Postgres where
+				// the schema was bootstrapped by a separate admin user. When the
+				// index exists from a prior run, treat that as success.
+				const hnswExists = await sql`
+					SELECT 1 FROM pg_class c
+					JOIN pg_namespace n ON n.oid = c.relnamespace
+					WHERE c.relkind = 'i'
+					  AND n.nspname = current_schema()
+					  AND c.relname = 'idx_entry_embedding_halfvec_hnsw'
+				`;
+				if (hnswExists.length === 0) {
+					try {
+						await sql.unsafe(`
+							CREATE INDEX IF NOT EXISTS idx_entry_embedding_halfvec_hnsw
+							ON knowledge_entry
+							USING hnsw ((embedding_vec::halfvec(${dims})) halfvec_cosine_ops)
+							WITH (m = 16, ef_construction = 64)
+						`);
+					} catch (err) {
+						logger.warn(
+							`[pg-db] Migration v17: ANN index creation skipped. ANN search disabled for this store. Error: ${err instanceof Error ? err.message : String(err)}`,
+						);
+					}
 				}
 			} else {
 				logger.warn(