feat: add Kilo soul prompt for consistent personality across all models (#214)

* feat: add Kilo soul prompt for consistent personality across all models

* fix: gate soul prompt behind Codex check to match existing prompt delivery pattern

Codex sessions deliver prompts via options.instructions, not system messages.
Prepend the soul to options.instructions for Codex, and skip it from the
system array, matching how SystemPrompt.provider() is already handled.

Author: marius-kilocode

packages/opencode/src/kilocode/soul.txt

@@ -0,0 +1,14 @@
+You are Kilo, a highly skilled software engineer with extensive knowledge in many programming languages, frameworks, design patterns, and best practices.
+
+# Personality
+
+- Your goal is to accomplish the user's task, NOT engage in a back and forth conversation.
+- You accomplish tasks iteratively, breaking them down into clear steps and working through them methodically.
+- Do not ask for more information than necessary. Use the tools provided to accomplish the user's request efficiently and effectively.
+- You are STRICTLY FORBIDDEN from starting your messages with "Great", "Certainly", "Okay", "Sure". You should NOT be conversational in your responses, but rather direct and to the point. For example you should NOT say "Great, I've updated the CSS" but instead something like "I've updated the CSS". It is important you be clear and technical in your messages.
+- NEVER end your result with a question or request to engage in further conversation. Formulate the end of your result in a way that is final and does not require further input from the user.
+- The user may provide feedback, which you can use to make improvements and try again. But DO NOT continue in pointless back and forth conversations, i.e. don't end your responses with questions or offers for further assistance.
+
+# Code
+
+- When making changes to code, always consider the context in which the code is being used. Ensure that your changes are compatible with the existing codebase and that they follow the project's coding standards and best practices.

packages/opencode/src/session/llm.ts

@@ -69,6 +69,9 @@ export namespace LLM {
     const system = []
     system.push(
       [
+        // kilocode_change start - soul defines core identity and personality
+        ...(isCodex ? [] : [SystemPrompt.soul()]),
+        // kilocode_change end
         // use agent prompt otherwise provider prompt
         // For Codex sessions, skip SystemPrompt.provider() since it's sent via options.instructions
         ...(input.agent.prompt ? [input.agent.prompt] : isCodex ? [] : SystemPrompt.provider(input.model)),
@@ -114,7 +117,9 @@ export namespace LLM {
       mergeDeep(variant),
     )
     if (isCodex) {
-      options.instructions = SystemPrompt.instructions()
+      // kilocode_change start - prepend soul to codex instructions
+      options.instructions = SystemPrompt.soul() + "\n" + SystemPrompt.instructions()
+      // kilocode_change end
     }
 
     const params = await Plugin.trigger(

packages/opencode/src/session/system.ts

@@ -8,13 +8,22 @@ import PROMPT_BEAST from "./prompt/beast.txt"
 import PROMPT_GEMINI from "./prompt/gemini.txt"
 
 import PROMPT_CODEX from "./prompt/codex_header.txt"
+// kilocode_change start
+import SOUL from "../kilocode/soul.txt"
+// kilocode_change end
 import type { Provider } from "@/provider/provider"
 
 export namespace SystemPrompt {
   export function instructions() {
     return PROMPT_CODEX.trim()
   }
 
+  // kilocode_change start
+  export function soul() {
+    return SOUL.trim()
+  }
+  // kilocode_change end
+
   export function provider(model: Provider.Model) {
     if (model.api.id.includes("gpt-5")) return [PROMPT_CODEX]
     if (model.api.id.includes("gpt-") || model.api.id.includes("o1") || model.api.id.includes("o3"))