refactor: narrow whatsapp chunking imports

src/plugin-sdk/reply-chunking.ts

@@ -1,4 +1,6 @@
 export {
+  chunkText,
+  chunkTextWithMode,
   chunkMarkdownTextWithMode,
   resolveChunkMode,
   resolveTextChunkLimit,

src/plugins/contracts/plugin-sdk-subpaths.test.ts

@@ -275,6 +275,8 @@ describe("plugin-sdk subpath exports", () => {
     ]) {
       expectSourceMentions(subpath, ["chunkTextForOutbound"]);
     }
+    expectSourceMentions("signal", ["chunkText"]);
+    expectSourceMentions("reply-chunking", ["chunkText", "chunkTextWithMode"]);
     expectSourceMentions("reply-history", [
       "buildPendingHistoryContextFromMap",
       "clearHistoryEntriesIfEnabled",