Update system prompt construction

Author: Nifury

packages/opencode/src/session/llm.ts

@@ -103,11 +103,11 @@ export namespace LLM {
     system.push(
       [
         // use agent prompt otherwise provider prompt
-        ...(input.agent.prompt ? [input.agent.prompt] : SystemPrompt.provider(input.model)),
+        ...(input.agent.prompt ? [input.agent.prompt] : (input.user.system ? [input.user.system] : SystemPrompt.provider(input.model))),
         // any custom prompt passed into this call
         ...input.system,
         // any custom prompt from last user message
-        ...(input.user.system ? [input.user.system] : []),
+        ...((input.agent.prompt && input.user.system) ? [input.user.system] : []),
       ]
         .filter((x) => x)
         .join("\n"),
@@ -131,10 +131,10 @@ export namespace LLM {
     const base = input.small
       ? ProviderTransform.smallOptions(input.model)
       : ProviderTransform.options({
-          model: input.model,
-          sessionID: input.sessionID,
-          providerOptions: provider.options,
-        })
+        model: input.model,
+        sessionID: input.sessionID,
+        providerOptions: provider.options,
+      })
     const options: Record<string, any> = pipe(
       base,
       mergeDeep(input.model.options),