ui: Filesystem @mentions for Chat Form (#26715)

* base : @-mention picker foundation - glob search, picker nav, highlight

* feat : @-mention file/folder picker and mention badges in message bubbles

* fix: Imports

* feat : wire the @-mention picker into the chat form

* fix: Bound the glob-search result cache key and prune stale entries

tools/ui/src/lib/constants/working-directory.ts

@@ -38,3 +38,9 @@ export const PATH_NAV_MAX_DEPTH = 1;
 // Native folder-picker resolution searches a shallow, bounded window.
 export const NATIVE_MAX_DEPTH = 4;
 export const NATIVE_LIMIT = 20;
+
+/** Upper bound the mention search depth setting accepts. The server itself imposes no depth cap (0 = unlimited); this is a UI sanity bound. */
+export const FILE_GLOB_SEARCH_PICKERS_MAX_SEARCH_DEPTH = 32;
+
+/** Depth the pickers fall back to when the user setting is invalid. */
+export const FILE_GLOB_SEARCH_PICKERS_DEFAULT_SEARCH_DEPTH = 10;