fix: store compress summary prefix at creation

Author: Tarquinen

lib/messages/prune.ts

@@ -2,7 +2,7 @@ import type { SessionState, WithParts } from "../state"
 import type { Logger } from "../logger"
 import type { PluginConfig } from "../config"
 import { isMessageCompacted, getLastUserMessage } from "../shared-utils"
-import { createSyntheticUserMessage, COMPRESS_SUMMARY_PREFIX } from "./utils"
+import { createSyntheticUserMessage } from "./utils"
 import type { UserMessage } from "@opencode-ai/sdk/v2"
 
 const PRUNED_TOOL_OUTPUT_REPLACEMENT =
@@ -186,7 +186,7 @@ const filterCompressedRanges = (
 
             if (userMessage) {
                 const userInfo = userMessage.info as UserMessage
-                const summaryContent = COMPRESS_SUMMARY_PREFIX + summary.summary
+                const summaryContent = summary.summary
                 result.push(
                     createSyntheticUserMessage(userMessage, summaryContent, userInfo.variant),
                 )

lib/tools/compress.ts

@@ -10,6 +10,7 @@ import { sendCompressNotification } from "../ui/notification"
 import { prune as applyPruneTransforms } from "../messages/prune"
 
 const COMPRESS_TOOL_DESCRIPTION = loadPrompt("compress-tool-spec")
+const COMPRESS_SUMMARY_PREFIX = "[Compressed conversation block]\n\n"
 
 export function createCompressTool(ctx: PruneToolContext): ReturnType<typeof tool> {
     return tool({
@@ -148,7 +149,7 @@ export function createCompressTool(ctx: PruneToolContext): ReturnType<typeof too
 
             const compressSummary: CompressSummary = {
                 anchorMessageId: startResult.messageId,
-                summary: summary,
+                summary: COMPRESS_SUMMARY_PREFIX + summary,
             }
             state.compressSummaries.push(compressSummary)