重构会话管理功能，由后端 opencode 发放 sessionId，后端做 scope

.opencode/tools/fetch_result_ref.ts

@@ -1,7 +1,10 @@
 import { tool } from "@opencode-ai/plugin";
+import { ToolSessionContextStore } from "../../src/session/toolContextStore.js";
 
 const internalBaseUrl = process.env.TJWATER_AGENT_INTERNAL_BASE_URL ?? "http://127.0.0.1:8787";
 const internalToken = process.env.TJWATER_AGENT_INTERNAL_TOKEN ?? "";
+const toolContextStore = new ToolSessionContextStore();
+const initializePromise = toolContextStore.initialize();
 
 export default tool({
   description:
@@ -19,6 +22,11 @@ export default tool({
       .describe("Optional maximum number of top-level items or fields to return."),
   },
   async execute(args, context) {
+    await initializePromise;
+    const sessionContext = await toolContextStore.read(context.sessionID);
+    if (!sessionContext) {
+      throw new Error(`session context not found for ${context.sessionID}`);
+    }
     const response = await fetch(`${internalBaseUrl}/internal/tools/fetch-result-ref`, {
       method: "POST",
       headers: {
@@ -26,7 +34,7 @@ export default tool({
         "x-agent-internal-token": internalToken,
       },
       body: JSON.stringify({
-        sessionId: context.sessionID,
+        sessionScopeKey: sessionContext.sessionScopeKey,
         result_ref: args.result_ref,
         max_items: args.max_items,
       }),