fix(sift): disable vector retriever + ML reranking to prevent hang

The sentence-transformers/all-MiniLM-L6-v2 embedding model inference hangs
indefinitely during sift search, causing:
- Warmup to never complete (TTL expired 62+ min ago)
- All page-index-hybrid searches to timeout
- The search cache to become stale

Fix: Restrict warmup and search to bm25+phrase retrievers with no ML
reranking. This gives fast lexical results while avoiding the hanging
embedding inference path.

Also expose --retrievers and --reranking params in sift_search tool so
callers can override per-query if needed.

Closes #vector-hang-fix

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

src/resources/extensions/sf/code-intelligence.js

@@ -554,6 +554,11 @@ export function ensureSiftIndexWarmup(projectRoot, prefs, options = {}) {
 		};
 	}
 	const scope = resolveSiftSearchScope(projectRoot, options.scope ?? ".");
+	// ── Vector retriever hang workaround ─────────────────────────────────────
+	// When the embedding model (sentence-transformers/all-MiniLM-L6-v2) hangs
+	// during inference, page-index-hybrid with vector retriever stalls forever.
+	// Restrict retrievers to bm25+phrase and disable ML reranking so warmup
+	// completes without the vector path (#vector-hang-fix).
 	const siftArgs = [
 		"search",
 		"--json",
@@ -565,6 +570,10 @@ export function ensureSiftIndexWarmup(projectRoot, prefs, options = {}) {
 		String(
 			options.retrieverTimeoutMs ?? DEFAULT_SIFT_WARMUP_RETRIEVER_TIMEOUT_MS,
 		),
+		"--retrievers",
+		"bm25,phrase",
+		"--reranking",
+		"none",
 		scope,
 		options.query ?? DEFAULT_SIFT_WARMUP_QUERY,
 	];

src/resources/extensions/sf/tools/sift-search-tool.js

@@ -54,6 +54,15 @@ function buildSiftArgs(params, projectRoot = process.cwd()) {
 		String(params.retrieverTimeoutMs ?? DEFAULT_RETRIEVER_TIMEOUT_MS),
 	];
 
+	// Allow callers to restrict retrievers (e.g. bm25,phrase) when the
+	// vector retriever or ML reranking is hanging (#vector-hang-fix).
+	if (params.retrievers) {
+		args.push("--retrievers", String(params.retrievers));
+	}
+	if (params.reranking) {
+		args.push("--reranking", String(params.reranking));
+	}
+
 	if (params.agent === true) {
 		args.push("--agent");
 		if (params.agentMode) {