fix: agent value passed to chat.params and chat.headers hooks was not a string (#19996)

packages/opencode/src/session/llm.ts

@@ -152,7 +152,7 @@ export namespace LLM {
       "chat.params",
       {
         sessionID: input.sessionID,
-        agent: input.agent,
+        agent: input.agent.name,
         model: input.model,
         provider,
         message: input.user,
@@ -171,7 +171,7 @@ export namespace LLM {
       "chat.headers",
       {
         sessionID: input.sessionID,
-        agent: input.agent,
+        agent: input.agent.name,
         model: input.model,
         provider,
         message: input.user,