fix(agent-tracing): populate thread_id from session_id in ClaudeAgentTracer

Claude SDK runs are manually constructed and don't have LangChain's
automatic metadata.thread_id. Use session_id as thread_id in
run.extra.metadata so getLogInfoPrefix can extract it consistently
across both LangGraph and Claude tracers.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jerryliang64

tegg/core/agent-tracing/src/ClaudeAgentTracer.ts

@@ -341,6 +341,9 @@ export class ClaudeAgentTracer {
       parent_run_id: undefined,
       tags: [],
       extra: {
+        metadata: {
+          thread_id: initMsg.session_id,
+        },
         apiKeySource: initMsg.apiKeySource,
         claude_code_version: initMsg.claude_code_version,
         output_style: initMsg.output_style,

tegg/core/agent-tracing/test/ClaudeAgentTracer.test.ts

@@ -218,6 +218,10 @@ describe('test/ClaudeAgentTracer.test.ts', () => {
       assert.strictEqual(traceIds.size, 1, `All runs should share one trace_id, got ${traceIds.size}`);
       assert.strictEqual([...traceIds][0], 'test-session-001', 'trace_id should match session_id');
 
+      // Root run should carry session_id as thread_id in extra.metadata
+      const rootExtra = rootStart.run.extra as Record<string, any>;
+      assert.strictEqual(rootExtra?.metadata?.thread_id, 'test-session-001', 'thread_id should match session_id');
+
       // Child runs reference root run as parent
       const childEntries = capturedRuns.filter((e) => !!e.run.parent_run_id);
       for (const child of childEntries) {