fix(codebase_search): disable vector retriever to prevent hang

The vector retriever in sift hangs indefinitely during embedding model
inference, causing all codebase_search calls to timeout. Apply the same
fix as sift_search: restrict retrievers to bm25+phrase and disable ML
reranking.

- buildCodebaseSearchArgs: add --retrievers bm25,phrase --reranking none
- Update tool description from (BM25 + Vector) to (BM25 + phrase)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/resources/extensions/sf/subagent/index.js

@@ -161,7 +161,22 @@ function isCodebaseSearchError(details) {
  * Consumer: `codebase_search.execute`.
  */
 function buildCodebaseSearchArgs(strategy, query, scope) {
-	return ["search", "--strategy", strategy, "--agent", query, scope];
+	// Restrict retrievers to bm25+phrase and disable ML reranking to avoid
+	// the vector retriever hang where embedding model inference stalls forever
+	// (#vector-hang-fix). This gives fast lexical results without the broken
+	// semantic path.
+	return [
+		"search",
+		"--strategy",
+		strategy,
+		"--retrievers",
+		"bm25,phrase",
+		"--reranking",
+		"none",
+		"--agent",
+		query,
+		scope,
+	];
 }
 function formatUsageStats(usage, model) {
 	const parts = [];
@@ -2502,7 +2517,7 @@ export default function (pi) {
 		name: "codebase_search",
 		label: "Code Search",
 		description: [
-			"Perform Sift-backed hybrid (BM25 + Vector) retrieval over a scoped codebase path.",
+			"Perform Sift-backed hybrid (BM25 + phrase) retrieval over a scoped codebase path.",
 			" Use this for conceptual, behavioral, or cross-cutting questions only after choosing a narrow scope",
 			" (e.g. 'how is X handled?', 'where is the logic for Y?', 'find examples of Z').",
 			" If Sift status is degraded or the scope is broad, prefer grep/find/ls and retry with a narrower scope.",