[Router] Add bucket-aware policy domains and native cache indexing (#38108)

Signed-off-by: Vincent Gao <vincentbo@linux.alibaba.com>
Co-authored-by: inkcherry <mingzhi.liu@amd.com>
Co-authored-by: yangbodong22011 <13137470+yangbodong22011@users.noreply.github.com>

experimental/sgl-router/tests/component/policies/cache_prefix_provider.rs

@@ -0,0 +1,52 @@
+// SPDX-FileCopyrightText: Copyright (c) 2026 The SGLang Authors
+// SPDX-License-Identifier: Apache-2.0
+
+use std::collections::HashMap;
+use std::sync::Arc;
+
+use sgl_kv_indexer::PrefixOutcome;
+use sgl_router::policies::kv_events::{
+    compute_block_hashes, BlockSizeOracle, HashTree, KvWorkerId,
+};
+use sgl_router::policies::prefix_provider::RadixTreePrefixProvider;
+
+#[test]
+fn radix_tree_reports_contiguous_prefix_depth_per_worker() {
+    let tokens = [11_u32, 12, 13, 14];
+    let hashes = compute_block_hashes(&tokens, 1);
+    let tree = Arc::new(HashTree::new());
+    let oracle = BlockSizeOracle::new();
+    oracle.try_set(1).unwrap();
+
+    tree.insert(&KvWorkerId::new("http://deep".into(), 0), None, &hashes);
+    tree.insert(
+        &KvWorkerId::new("http://deep".into(), 1),
+        None,
+        &hashes[..3],
+    );
+    tree.insert(
+        &KvWorkerId::new("http://shallow".into(), 0),
+        None,
+        &hashes[..2],
+    );
+
+    let signal = RadixTreePrefixProvider::new(tree, oracle)
+        .match_request_tokens(&tokens)
+        .expect("established local tree must produce a prefix signal");
+    let PrefixOutcome::Matched {
+        matches,
+        best_prefix_blocks,
+    } = signal.outcome
+    else {
+        panic!("local radix-tree hit must be normalized as a match");
+    };
+    let depth_by_url: HashMap<_, _> = matches
+        .into_iter()
+        .map(|entry| (entry.address, entry.matched_prefix_blocks))
+        .collect();
+
+    assert_eq!(signal.query_blocks, 4);
+    assert_eq!(best_prefix_blocks, 4);
+    assert_eq!(depth_by_url.get("http://deep"), Some(&4));
+    assert_eq!(depth_by_url.get("http://shallow"), Some(&2));
+}