feat: add model self-identification to system prompt

Prepend assistant info line between header and agent prompt so models
know what they are and what version of OpenCode they're running in.

Format: "You are {name} ({provider}: {id}) running in OpenCode v{version},
the best coding agent on the planet."

Author: ferdinandyb

packages/opencode/src/session/llm.ts

@@ -47,8 +47,10 @@ export namespace LLM {
     const [language, cfg] = await Promise.all([Provider.getLanguage(input.model), Config.get()])
 
     const system = SystemPrompt.header(input.model.providerID)
+    const assistantInfo = await SystemPrompt.assistantInfo(input.model)
     system.push(
       [
+        assistantInfo,
         // use agent prompt otherwise provider prompt
         ...(input.agent.prompt ? [input.agent.prompt] : SystemPrompt.provider(input.model)),
         // any custom prompt passed into this call

packages/opencode/src/session/system.ts

@@ -2,6 +2,8 @@ import { Ripgrep } from "../file/ripgrep"
 import { Global } from "../global"
 import { Filesystem } from "../util/filesystem"
 import { Config } from "../config/config"
+import { Installation } from "../installation"
+import { Provider } from "../provider/provider"
 
 import { Instance } from "../project/instance"
 import path from "path"
@@ -14,14 +16,19 @@ import PROMPT_GEMINI from "./prompt/gemini.txt"
 import PROMPT_ANTHROPIC_SPOOF from "./prompt/anthropic_spoof.txt"
 
 import PROMPT_CODEX from "./prompt/codex.txt"
-import type { Provider } from "@/provider/provider"
 
 export namespace SystemPrompt {
   export function header(providerID: string) {
     if (providerID.includes("anthropic")) return [PROMPT_ANTHROPIC_SPOOF.trim()]
     return []
   }
 
+  export async function assistantInfo(model?: Provider.Model) {
+    if (!model) return `You are running in OpenCode v${Installation.VERSION}, the best coding agent on the planet.`
+    const provider = await Provider.getProvider(model.providerID)
+    return `You are ${model.name} (${provider.name}: ${model.id}) running in OpenCode v${Installation.VERSION}, the best coding agent on the planet.`
+  }
+
   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"))