refactor: make synthetic injection IDs deterministic

Author: Tarquinen

lib/messages/prune.ts

@@ -187,8 +187,14 @@ const filterCompressedRanges = (
             if (userMessage) {
                 const userInfo = userMessage.info as UserMessage
                 const summaryContent = summary.summary
+                const summarySeed = `${summary.blockId}:${summary.anchorMessageId}`
                 result.push(
-                    createSyntheticUserMessage(userMessage, summaryContent, userInfo.variant),
+                    createSyntheticUserMessage(
+                        userMessage,
+                        summaryContent,
+                        userInfo.variant,
+                        summarySeed,
+                    ),
                 )
 
                 logger.info("Injected compress summary", {

lib/messages/utils.ts

@@ -1,9 +1,14 @@
-import { ulid } from "ulid"
+import { createHash } from "node:crypto"
 import { isMessageCompacted } from "../shared-utils"
 import type { SessionState, WithParts } from "../state"
 import type { UserMessage } from "@opencode-ai/sdk/v2"
 
-const generateUniqueId = (prefix: string): string => `${prefix}_${ulid()}`
+const SUMMARY_ID_HASH_LENGTH = 16
+
+const generateStableId = (prefix: string, seed: string): string => {
+    const hash = createHash("sha256").update(seed).digest("hex").slice(0, SUMMARY_ID_HASH_LENGTH)
+    return `${prefix}_${hash}`
+}
 
 const isGeminiModel = (modelID: string): boolean => {
     const lowerModelID = modelID.toLowerCase()
@@ -14,11 +19,13 @@ export const createSyntheticUserMessage = (
     baseMessage: WithParts,
     content: string,
     variant?: string,
+    stableSeed?: string,
 ): WithParts => {
     const userInfo = baseMessage.info as UserMessage
     const now = Date.now()
-    const messageId = generateUniqueId("msg")
-    const partId = generateUniqueId("prt")
+    const deterministicSeed = stableSeed?.trim() || userInfo.id
+    const messageId = generateStableId("msg_dcp_summary", deterministicSeed)
+    const partId = generateStableId("prt_dcp_summary", deterministicSeed)
 
     return {
         info: {
@@ -42,9 +49,14 @@ export const createSyntheticUserMessage = (
     }
 }
 
-export const createSyntheticTextPart = (baseMessage: WithParts, content: string) => {
+export const createSyntheticTextPart = (
+    baseMessage: WithParts,
+    content: string,
+    stableSeed?: string,
+) => {
     const userInfo = baseMessage.info as UserMessage
-    const partId = generateUniqueId("prt")
+    const deterministicSeed = stableSeed?.trim() || userInfo.id
+    const partId = generateStableId("prt_dcp_text", deterministicSeed)
 
     return {
         id: partId,
@@ -59,12 +71,14 @@ export const createSyntheticToolPart = (
     baseMessage: WithParts,
     content: string,
     modelID: string,
+    stableSeed?: string,
 ) => {
     const userInfo = baseMessage.info as UserMessage
     const now = Date.now()
 
-    const partId = generateUniqueId("prt")
-    const callId = generateUniqueId("call")
+    const deterministicSeed = stableSeed?.trim() || userInfo.id
+    const partId = generateStableId("prt_dcp_tool", deterministicSeed)
+    const callId = generateStableId("call_dcp_tool", deterministicSeed)
 
     // Gemini requires thoughtSignature bypass to accept synthetic tool parts
     const toolPartMetadata = isGeminiModel(modelID)

package-lock.json

@@ -46,7 +46,6 @@
         "@opencode-ai/sdk": "^1.1.48",
         "fuzzball": "^2.2.3",
         "jsonc-parser": "^3.3.1",
-        "ulid": "^3.0.2",
         "zod": "^4.3.6"
     },
     "devDependencies": {