refactor(session): stop injecting provider-specific prompts into system message

Author: sdeonvacation

packages/opencode/src/session/llm.ts

@@ -160,8 +160,8 @@ export namespace LLM {
     const system: string[] = []
     system.push(
       [
-        // use agent prompt otherwise provider prompt
-        ...(input.agent.prompt ? [input.agent.prompt] : SystemPrompt.provider(model)),
+        // use agent prompt if set
+        ...(input.agent.prompt ? [input.agent.prompt] : []),
         // any custom prompt passed into this call
         ...input.system,
         // any custom prompt from last user message