fix(cache): add splitSystemPrompt provider option to opt out of system block split

Author: bhagirathsinh-vaghela

packages/opencode/src/session/llm.ts

@@ -70,12 +70,17 @@ export namespace LLM {
 
     const prompt = input.agent.prompt ? [input.agent.prompt] : isOpenaiOauth ? [] : SystemPrompt.provider(input.model)
     const split = input.systemSplit ?? input.system.length
-    const system = [
-      // block 1: provider/agent prompt + global instructions (stable across repos)
-      [...prompt, ...input.system.slice(0, split)].filter(Boolean).join("\n"),
-      // block 2: env + project instructions + any custom prompt from last user message (dynamic)
-      [...input.system.slice(split), ...(input.user.system ? [input.user.system] : [])].filter(Boolean).join("\n"),
-    ].filter(Boolean)
+    const shouldSplit = provider.options?.["splitSystemPrompt"] !== false
+    const system = shouldSplit
+      ? [
+          // block 1: provider/agent prompt + global instructions (stable across repos)
+          [...prompt, ...input.system.slice(0, split)].filter(Boolean).join("\n"),
+          // block 2: env + project instructions + any custom prompt from last user message (dynamic)
+          [...input.system.slice(split), ...(input.user.system ? [input.user.system] : [])].filter(Boolean).join("\n"),
+        ].filter(Boolean)
+      : [
+          [...prompt, ...input.system, ...(input.user.system ? [input.user.system] : [])].filter(Boolean).join("\n"),
+        ].filter(Boolean)
 
     const header = system[0]
     await Plugin.trigger(
@@ -84,7 +89,7 @@ export namespace LLM {
       { system },
     )
     // rejoin to maintain 2-part structure for caching if header unchanged
-    if (system.length > 2 && system[0] === header) {
+    if (shouldSplit && system.length > 2 && system[0] === header) {
       const rest = system.slice(1)
       system.length = 0
       system.push(header, rest.join("\n"))