Merge pull request #249 from Opencode-DCP/fix/skip-subagent-system-prompt-injection

fix: skip system prompt injection for subagent sessions

Author: Tarquinen

index.ts

@@ -1,10 +1,9 @@
 import type { Plugin } from "@opencode-ai/plugin"
 import { getConfig } from "./lib/config"
 import { Logger } from "./lib/logger"
-import { loadPrompt } from "./lib/prompts"
 import { createSessionState } from "./lib/state"
 import { createDiscardTool, createExtractTool } from "./lib/strategies"
-import { createChatMessageTransformHandler } from "./lib/hooks"
+import { createChatMessageTransformHandler, createSystemPromptHandler } from "./lib/hooks"
 
 const plugin: Plugin = (async (ctx) => {
     const config = getConfig(ctx)
@@ -13,11 +12,6 @@ const plugin: Plugin = (async (ctx) => {
         return {}
     }
 
-    // Suppress AI SDK warnings
-    if (typeof globalThis !== "undefined") {
-        ;(globalThis as any).AI_SDK_LOG_WARNINGS = false
-    }
-
     const logger = new Logger(config.debug)
     const state = createSessionState()
 
@@ -26,38 +20,8 @@ const plugin: Plugin = (async (ctx) => {
     })
 
     return {
-        "experimental.chat.system.transform": async (
-            _input: unknown,
-            output: { system: string[] },
-        ) => {
-            const systemText = output.system.join("\n")
-            const internalAgentSignatures = [
-                "You are a title generator",
-                "You are a helpful AI assistant tasked with summarizing conversations",
-                "Summarize what was done in this conversation",
-            ]
-            if (internalAgentSignatures.some((sig) => systemText.includes(sig))) {
-                logger.info("Skipping DCP system prompt injection for internal agent")
-                return
-            }
+        "experimental.chat.system.transform": createSystemPromptHandler(state, logger, config),
 
-            const discardEnabled = config.tools.discard.enabled
-            const extractEnabled = config.tools.extract.enabled
-
-            let promptName: string
-            if (discardEnabled && extractEnabled) {
-                promptName = "user/system/system-prompt-both"
-            } else if (discardEnabled) {
-                promptName = "user/system/system-prompt-discard"
-            } else if (extractEnabled) {
-                promptName = "user/system/system-prompt-extract"
-            } else {
-                return
-            }
-
-            const syntheticPrompt = loadPrompt(promptName)
-            output.system.push(syntheticPrompt)
-        },
         "experimental.chat.messages.transform": createChatMessageTransformHandler(
             ctx.client,
             state,

lib/hooks.ts

@@ -5,6 +5,48 @@ import { syncToolCache } from "./state/tool-cache"
 import { deduplicate, supersedeWrites, purgeErrors } from "./strategies"
 import { prune, insertPruneToolContext } from "./messages"
 import { checkSession } from "./state"
+import { loadPrompt } from "./prompts"
+
+const INTERNAL_AGENT_SIGNATURES = [
+    "You are a title generator",
+    "You are a helpful AI assistant tasked with summarizing conversations",
+    "Summarize what was done in this conversation",
+]
+
+export function createSystemPromptHandler(
+    state: SessionState,
+    logger: Logger,
+    config: PluginConfig,
+) {
+    return async (_input: unknown, output: { system: string[] }) => {
+        if (state.isSubAgent) {
+            return
+        }
+
+        const systemText = output.system.join("\n")
+        if (INTERNAL_AGENT_SIGNATURES.some((sig) => systemText.includes(sig))) {
+            logger.info("Skipping DCP system prompt injection for internal agent")
+            return
+        }
+
+        const discardEnabled = config.tools.discard.enabled
+        const extractEnabled = config.tools.extract.enabled
+
+        let promptName: string
+        if (discardEnabled && extractEnabled) {
+            promptName = "user/system/system-prompt-both"
+        } else if (discardEnabled) {
+            promptName = "user/system/system-prompt-discard"
+        } else if (extractEnabled) {
+            promptName = "user/system/system-prompt-extract"
+        } else {
+            return
+        }
+
+        const syntheticPrompt = loadPrompt(promptName)
+        output.system.push(syntheticPrompt)
+    }
+}
 
 export function createChatMessageTransformHandler(
     client: any,