diff --git a/packages/app/src/context/global-sync/event-reducer.test.ts b/packages/app/src/context/global-sync/event-reducer.test.ts
index b53fb691b3c..06d536618e0 100644
--- a/packages/app/src/context/global-sync/event-reducer.test.ts
+++ b/packages/app/src/context/global-sync/event-reducer.test.ts
@@ -15,12 +15,12 @@ const rootSession = (input: { id: string; parentID?: string; archived?: number }
     },
   }) as Session
 
-const userMessage = (id: string, sessionID: string) =>
+const userMessage = (id: string, sessionID: string, created = 1) =>
   ({
     id,
     sessionID,
     role: "user",
-    time: { created: 1 },
+    time: { created },
     agent: "assistant",
     model: { providerID: "openai", modelID: "gpt" },
   }) as Message
@@ -370,13 +370,13 @@ describe("applyDirectoryEvent", () => {
     const sessionID = "ses_1"
     const [store, setStore] = createStore(
       baseState({
-        message: { [sessionID]: [userMessage("msg_1", sessionID), userMessage("msg_3", sessionID)] },
-        part: { msg_2: [textPart("prt_1", sessionID, "msg_2")] },
+        message: { [sessionID]: [userMessage("msg_z", sessionID, 1), userMessage("msg_b", sessionID, 3)] },
+        part: { msg_a: [textPart("prt_1", sessionID, "msg_a")] },
       }),
     )
 
     applyDirectoryEvent({
-      event: { type: "message.updated", properties: { info: userMessage("msg_2", sessionID) } },
+      event: { type: "message.updated", properties: { info: userMessage("msg_a", sessionID, 2) } },
       store,
       setStore,
       push() {},
@@ -384,14 +384,14 @@ describe("applyDirectoryEvent", () => {
       loadLsp() {},
     })
 
-    expect(store.message[sessionID]?.map((x) => x.id)).toEqual(["msg_1", "msg_2", "msg_3"])
+    expect(store.message[sessionID]?.map((x) => x.id)).toEqual(["msg_z", "msg_a", "msg_b"])
 
     applyDirectoryEvent({
       event: {
         type: "message.updated",
         properties: {
           info: {
-            ...userMessage("msg_2", sessionID),
+            ...userMessage("msg_a", sessionID, 2),
             role: "assistant",
           } as Message,
         },
@@ -403,10 +403,10 @@ describe("applyDirectoryEvent", () => {
       loadLsp() {},
     })
 
-    expect(store.message[sessionID]?.find((x) => x.id === "msg_2")?.role).toBe("assistant")
+    expect(store.message[sessionID]?.find((x) => x.id === "msg_a")?.role).toBe("assistant")
 
     applyDirectoryEvent({
-      event: { type: "message.removed", properties: { sessionID, messageID: "msg_2" } },
+      event: { type: "message.removed", properties: { sessionID, messageID: "msg_a" } },
       store,
       setStore,
       push() {},
@@ -414,8 +414,8 @@ describe("applyDirectoryEvent", () => {
       loadLsp() {},
     })
 
-    expect(store.message[sessionID]?.map((x) => x.id)).toEqual(["msg_1", "msg_3"])
-    expect(store.part.msg_2).toBeUndefined()
+    expect(store.message[sessionID]?.map((x) => x.id)).toEqual(["msg_z", "msg_b"])
+    expect(store.part.msg_a).toBeUndefined()
   })
 
   test("upserts and prunes message parts", () => {
diff --git a/packages/app/src/context/global-sync/event-reducer.ts b/packages/app/src/context/global-sync/event-reducer.ts
index 8f203715a6d..b84d5201cf5 100644
--- a/packages/app/src/context/global-sync/event-reducer.ts
+++ b/packages/app/src/context/global-sync/event-reducer.ts
@@ -15,6 +15,7 @@ import type { State, VcsCache } from "./types"
 import { trimSessions } from "./session-trim"
 import { dropSessionCaches } from "./session-cache"
 import { diffs as list, message as clean } from "@/utils/diffs"
+import { messageKey } from "@/utils/session-message"
 
 const SKIP_PARTS = new Set(["patch", "step-start", "step-finish"])
 const SESSION_CONTENT_EVENTS = new Set([
@@ -275,7 +276,7 @@ export function applyDirectoryEvent(input: {
         input.setStore("message", info.sessionID, [info])
         break
       }
-      const result = Binary.search(messages, info.id, (m) => m.id)
+      const result = Binary.search(messages, messageKey(info), messageKey)
       if (result.found) {
         input.setStore("message", info.sessionID, result.index, reconcile(info))
         break
@@ -295,8 +296,8 @@ export function applyDirectoryEvent(input: {
         produce((draft) => {
           const messages = draft.message[props.sessionID]
           if (messages) {
-            const result = Binary.search(messages, props.messageID, (m) => m.id)
-            if (result.found) messages.splice(result.index, 1)
+            const index = messages.findIndex((message) => message.id === props.messageID)
+            if (index >= 0) messages.splice(index, 1)
           }
           const parts = draft.part[props.messageID]
           if (parts) {
@@ -322,7 +323,7 @@ export function applyDirectoryEvent(input: {
         input.setStore("part", part.messageID, [part])
         break
       }
-      const result = Binary.search(parts, part.id, (p) => p.id)
+      const result = Binary.search(parts, part.id, (item) => item.id)
       if (result.found) {
         input.setStore("part", part.messageID, result.index, reconcile(part))
         break
@@ -345,13 +346,13 @@ export function applyDirectoryEvent(input: {
       )
       const parts = input.store.part[props.messageID]
       if (!parts) break
-      const result = Binary.search(parts, props.partID, (p) => p.id)
+      const result = Binary.search(parts, props.partID, (part) => part.id)
       if (result.found) {
         input.setStore(
           produce((draft) => {
             const list = draft.part[props.messageID]
             if (!list) return
-            const next = Binary.search(list, props.partID, (p) => p.id)
+            const next = Binary.search(list, props.partID, (part) => part.id)
             if (!next.found) return
             list.splice(next.index, 1)
             if (list.length === 0) delete draft.part[props.messageID]
@@ -364,7 +365,7 @@ export function applyDirectoryEvent(input: {
       const props = event.properties as { messageID: string; partID: string; field: string; delta: string }
       const parts = input.store.part[props.messageID]
       if (!parts) break
-      const result = Binary.search(parts, props.partID, (p) => p.id)
+      const result = Binary.search(parts, props.partID, (part) => part.id)
       if (!result.found) break
       const field = props.field as keyof (typeof parts)[number]
       const current = parts[result.index]?.[field]
diff --git a/packages/app/src/context/server-session.test.ts b/packages/app/src/context/server-session.test.ts
index e9595e13760..2ebf5f88ef0 100644
--- a/packages/app/src/context/server-session.test.ts
+++ b/packages/app/src/context/server-session.test.ts
@@ -264,6 +264,7 @@ describe("server session", () => {
 
     expect(requests).toEqual([{ sessionID: "root", limit: 20, order: "desc" }])
     expect(store.data.session_message.root.map((message) => message.id)).toEqual([user.id, assistant.id])
+    expect(store.data.message.root.map((message) => message.id)).toEqual([user.id, assistant.id])
   })
 
   test("extends a current page to include the user for split assistant turns", async () => {
@@ -1497,7 +1498,7 @@ describe("server session", () => {
 
     await store.sync("child", { force: true })
 
-    expect(store.data.message.child).toEqual([boundary, older])
+    expect(store.data.message.child).toEqual([older, boundary])
   })
 
   test("preserves a part update for a message being loaded from history", async () => {
diff --git a/packages/app/src/context/server-session.ts b/packages/app/src/context/server-session.ts
index 69bec61ba2f..c5d98682f03 100644
--- a/packages/app/src/context/server-session.ts
+++ b/packages/app/src/context/server-session.ts
@@ -18,7 +18,7 @@ import { message as cleanMessage } from "@/utils/diffs"
 import { sessionNotFoundError } from "@/utils/server-errors"
 import { rootSession } from "@/utils/session-route"
 import { normalizeSessionInfo } from "@/utils/session"
-import { normalizeSessionMessages } from "@/utils/session-message"
+import { compareMessages, messageKey, normalizeSessionMessages } from "@/utils/session-message"
 import { dropSessionCaches, pickSessionCacheEvictions, SESSION_CACHE_LIMIT } from "./global-sync/session-cache"
 import { createV2SessionReducer, type V2SessionReduction } from "./server-session-v2-reducer"
 import type { ServerApi } from "@/utils/server"
@@ -26,7 +26,6 @@ import type { ServerApi } from "@/utils/server"
 type MessageApi = ServerApi["message"]
 
 const cmp = (a: string, b: string) => (a < b ? -1 : a > b ? 1 : 0)
-const cmpMessage = (a: Message, b: Message) => a.time.created - b.time.created || cmp(a.id, b.id)
 const SKIP_PARTS = new Set(["patch", "step-start", "step-finish"])
 const initialMessagePageSize = 20
 const historyMessagePageSize = 200
@@ -64,7 +63,7 @@ type MessagePage = {
 function legacyMessageSource(items: { info: Message; parts: Part[] }[]): SessionMessageInfo[] {
   return items
     .slice()
-    .sort((a, b) => cmp(a.info.id, b.info.id))
+    .sort((a, b) => compareMessages(a.info, b.info))
     .map((item) => {
       if (item.info.role === "user") {
         return {
@@ -111,17 +110,16 @@ function mergeOptimisticPage(page: MessagePage, items: OptimisticItem[]) {
   const part = new Map(page.part.map((item) => [item.id, item.part]))
   const observed: { messageID: string; parts: Part[] }[] = []
   for (const item of items) {
-    const result = Binary.search(session, item.message.id, (message) => message.id)
-    if (!result.found) session.splice(result.index, 0, item.message)
+    const result = Binary.search(session, messageKey(item.message), messageKey)
+    const found = result.found
+    if (!found) session.splice(result.index, 0, item.message)
     const current = part.get(item.message.id)
-    const confirmed = result.found
-      ? item.parts.filter((part) => Binary.search(current ?? [], part.id, (value) => value.id).found)
-      : []
-    if (result.found) observed.push({ messageID: item.message.id, parts: confirmed })
+    const confirmed = found ? item.parts.filter((part) => current?.some((value) => value.id === part.id)) : []
+    if (found) observed.push({ messageID: item.message.id, parts: confirmed })
     part.set(
       item.message.id,
       merge(
-        result.found ? (current ?? []) : merge(item.confirmedParts ?? [], current ?? []),
+        found ? (current ?? []) : merge(item.confirmedParts ?? [], current ?? []),
         item.parts.filter((part) => !confirmed.includes(part)),
       ),
     )
@@ -158,6 +156,7 @@ function reconcileFetched<T extends { id: string }>(
     retained?: ReadonlySet<string>
     removed?: ReadonlySet<string>
     preserveUnfetched?: boolean | ((item: T) => boolean)
+    compare?: (a: T, b: T) => number
   } = {},
 ) {
   const result = new Map(fetched.map((item) => [item.id, item]))
@@ -180,7 +179,8 @@ function reconcileFetched<T extends { id: string }>(
     if (!item) result.delete(id)
   }
   for (const id of options.removed ?? emptyIDs) result.delete(id)
-  return [...result.values()].sort((a, b) => cmp(a.id, b.id))
+  const items = [...result.values()]
+  return options.compare ? items.sort(options.compare) : items
 }
 
 type ServerSessionOptions = { retry?: typeof retry; protocol?: Promise<"v1" | "v2"> }
@@ -413,8 +413,7 @@ export function createServerSession(
     if (!load) return
     // A part event keeps an existing parent when the fetched page omits it without overriding fetched metadata.
     const messages = data.message[sessionID]
-    if (messages && Binary.search(messages, messageID, (message) => message.id).found)
-      load.retainedMessages.add(messageID)
+    if (messages?.some((message) => message.id === messageID)) load.retainedMessages.add(messageID)
     const parts = load.touchedParts.get(messageID)
     if (parts) {
       parts.add(partID)
@@ -437,16 +436,14 @@ export function createServerSession(
       load.touchedParts.set(messageID, new Set(parts))
       load.carriedDeltaParts.set(messageID, new Set(parts))
       const messages = data.message[sessionID]
-      if (messages && Binary.search(messages, messageID, (message) => message.id).found)
-        load.retainedMessages.add(messageID)
+      if (messages?.some((message) => message.id === messageID)) load.retainedMessages.add(messageID)
     }
     for (const [messageID, parts] of load.removedParts) {
       const touched = load.touchedParts.get(messageID) ?? new Set<string>()
       parts.forEach((partID) => touched.add(partID))
       load.touchedParts.set(messageID, touched)
       const messages = data.message[sessionID]
-      if (messages && Binary.search(messages, messageID, (message) => message.id).found)
-        load.retainedMessages.add(messageID)
+      if (messages?.some((message) => message.id === messageID)) load.retainedMessages.add(messageID)
     }
     for (const [messageID, parts] of load.optimisticParts) {
       load.removedMessages.delete(messageID)
@@ -555,7 +552,7 @@ export function createServerSession(
       const source = pages.flatMap((page) => page.data).toReversed()
       const normalized = normalizeSessionMessages(sessionID, source)
       return {
-        session: normalized.messages.sort((a, b) => cmp(a.id, b.id)),
+        session: normalized.messages.sort(compareMessages),
         part: [...normalized.parts.entries()]
           .map(([id, part]) => ({ id, part: part.sort((a, b) => cmp(a.id, b.id)) }))
           .sort((a, b) => cmp(a.id, b.id)),
@@ -572,7 +569,7 @@ export function createServerSession(
     })
     const items = (response.data ?? []).filter((item) => !!item?.info?.id)
     return {
-      session: items.map((item) => cleanMessage(item.info)).sort((a, b) => cmp(a.id, b.id)),
+      session: items.map((item) => cleanMessage(item.info)).sort(compareMessages),
       part: items.map((item) => ({
         id: item.info.id,
         part: item.parts.filter((part) => !!part?.id).sort((a, b) => cmp(a.id, b.id)),
@@ -696,7 +693,7 @@ export function createServerSession(
             const normalized = normalizeSessionMessages(sessionID, source)
             return {
               ...page,
-              session: normalized.messages.sort((a, b) => cmp(a.id, b.id)),
+              session: normalized.messages.sort(compareMessages),
               part: [...normalized.parts.entries()]
                 .map(([id, part]) => ({ id, part: part.sort((a, b) => cmp(a.id, b.id)) }))
                 .sort((a, b) => cmp(a.id, b.id)),
@@ -713,6 +710,7 @@ export function createServerSession(
       retained: load?.retainedMessages,
       removed: load?.removedMessages,
       preserveUnfetched,
+      compare: compareMessages,
     })
     batch(() => {
       if (source) setData("session_message", sessionID, reconcile(source))
@@ -754,7 +752,7 @@ export function createServerSession(
     try {
       const page = await fetchMessages(sessionID, limit, before, () => resetMessageLoad(sessionID, load))
       const first = page.session.reduce<Message | undefined>(
-        (oldest, message) => (!oldest || cmpMessage(message, oldest) < 0 ? message : oldest),
+        (oldest, message) => (!oldest || compareMessages(message, oldest) < 0 ? message : oldest),
         undefined,
       )
       if (generations.get(sessionID) !== active) return
@@ -804,14 +802,15 @@ export function createServerSession(
               session: merge(
                 page.session,
                 parents.map((parent) => parent.message),
-              ),
+              ).sort(compareMessages),
               part: merge(
                 page.part,
                 parents.map((parent) => ({ id: parent.message.id, part: parent.parts })),
               ),
             }
       const preserveUnfetched =
-        mode === "prepend" || (!result.complete && (!first || ((message: Message) => cmpMessage(message, first) < 0)))
+        mode === "prepend" ||
+        (!result.complete && (!first || ((message: Message) => compareMessages(message, first) < 0)))
       applyMessagePage(
         sessionID,
         result,
@@ -928,7 +927,7 @@ export function createServerSession(
       .message({ sessionID, messageID })
       .then((message) => {
         const current = data.session_message[sessionID] ?? []
-        const messages = [...current.filter((item) => item.id !== message.id), message].sort((a, b) => cmp(a.id, b.id))
+        const messages = [...current.filter((item) => item.id !== message.id), message].sort(compareMessages)
         projectV2({ sessionID, messages, touched: [message.id] })
       })
       .catch(() => {})
@@ -1051,7 +1050,7 @@ export function createServerSession(
           setData("message", info.sessionID, [info])
           return
         }
-        const result = Binary.search(messages, info.id, (message) => message.id)
+        const result = Binary.search(messages, messageKey(info), messageKey)
         if (result.found) setData("message", info.sessionID, result.index, reconcile(info))
         if (!result.found)
           setData("message", info.sessionID, (value = []) => {
@@ -1084,8 +1083,8 @@ export function createServerSession(
           produce((draft) => {
             const messages = draft.message[props.sessionID]
             if (messages) {
-              const result = Binary.search(messages, props.messageID, (message) => message.id)
-              if (result.found) messages.splice(result.index, 1)
+              const index = messages.findIndex((message) => message.id === props.messageID)
+              if (index >= 0) messages.splice(index, 1)
             }
             deleteMessageParts(draft, props.messageID)
           }),
@@ -1097,7 +1096,7 @@ export function createServerSession(
         if (SKIP_PARTS.has(part.type)) return
         const messages = data.message[part.sessionID]
         const load = messageLoads.get(part.sessionID)
-        const missing = !messages || !Binary.search(messages, part.messageID, (message) => message.id).found
+        const missing = !messages?.some((message) => message.id === part.messageID)
         // Outside a page load, accepting a part without its ordered parent event would create an unbounded orphan.
         if (
           missing &&
@@ -1341,7 +1340,7 @@ export function createServerSession(
         if (items) items.set(input.message.id, { ...input, parts, confirmedParts: [] })
         if (!items)
           optimistic.set(input.sessionID, new Map([[input.message.id, { ...input, parts, confirmedParts: [] }]]))
-        setData("message", input.sessionID, (messages = []) => merge(messages, [input.message]))
+        setData("message", input.sessionID, (messages = []) => merge(messages, [input.message]).sort(compareMessages))
         setData(
           "part_text_accum_delta",
           produce((draft) => {
diff --git a/packages/app/src/context/sync-optimistic.test.ts b/packages/app/src/context/sync-optimistic.test.ts
index 94324f8a060..d7ac9fd9641 100644
--- a/packages/app/src/context/sync-optimistic.test.ts
+++ b/packages/app/src/context/sync-optimistic.test.ts
@@ -4,11 +4,11 @@ import { applyOptimisticAdd, applyOptimisticRemove, mergeOptimisticPage } from "
 
 type Text = Extract<Part, { type: "text" }>
 
-const userMessage = (id: string, sessionID: string): Message => ({
+const userMessage = (id: string, sessionID: string, created = 1): Message => ({
   id,
   sessionID,
   role: "user",
-  time: { created: 1 },
+  time: { created },
   agent: "assistant",
   model: { providerID: "openai", modelID: "gpt" },
 })
@@ -22,21 +22,21 @@ const textPart = (id: string, sessionID: string, messageID: string): Text => ({
 })
 
 describe("sync optimistic reducers", () => {
-  test("applyOptimisticAdd inserts message in sorted order and stores parts", () => {
+  test("applyOptimisticAdd inserts by creation time", () => {
     const sessionID = "ses_1"
     const draft = {
-      message: { [sessionID]: [userMessage("msg_2", sessionID)] },
+      message: { [sessionID]: [userMessage("msg_z", sessionID, 1)] },
       part: {} as Record<string, Part[] | undefined>,
     }
 
     applyOptimisticAdd(draft, {
       sessionID,
-      message: userMessage("msg_1", sessionID),
-      parts: [textPart("prt_2", sessionID, "msg_1"), textPart("prt_1", sessionID, "msg_1")],
+      message: userMessage("msg_a", sessionID, 2),
+      parts: [textPart("prt_2", sessionID, "msg_a"), textPart("prt_1", sessionID, "msg_a")],
     })
 
-    expect(draft.message[sessionID]?.map((x) => x.id)).toEqual(["msg_1", "msg_2"])
-    expect(draft.part.msg_1?.map((x) => x.id)).toEqual(["prt_1", "prt_2"])
+    expect(draft.message[sessionID]?.map((x) => x.id)).toEqual(["msg_z", "msg_a"])
+    expect(draft.part.msg_a?.map((x) => x.id)).toEqual(["prt_1", "prt_2"])
   })
 
   test("applyOptimisticRemove removes message and part entries", () => {
@@ -60,19 +60,33 @@ describe("sync optimistic reducers", () => {
     const sessionID = "ses_1"
     const page = mergeOptimisticPage(
       {
-        session: [userMessage("msg_1", sessionID)],
-        part: [{ id: "msg_1", part: [textPart("prt_1", sessionID, "msg_1")] }],
+        session: [userMessage("msg_z", sessionID, 1)],
+        part: [{ id: "msg_z", part: [textPart("prt_1", sessionID, "msg_z")] }],
         complete: true,
       },
-      [{ message: userMessage("msg_2", sessionID), parts: [textPart("prt_2", sessionID, "msg_2")] }],
+      [{ message: userMessage("msg_a", sessionID, 2), parts: [textPart("prt_2", sessionID, "msg_a")] }],
     )
 
-    expect(page.session.map((x) => x.id)).toEqual(["msg_1", "msg_2"])
-    expect(page.part.find((x) => x.id === "msg_2")?.part.map((x) => x.id)).toEqual(["prt_2"])
+    expect(page.session.map((x) => x.id)).toEqual(["msg_z", "msg_a"])
+    expect(page.part.find((x) => x.id === "msg_a")?.part.map((x) => x.id)).toEqual(["prt_2"])
     expect(page.confirmed).toEqual([])
     expect(page.complete).toBe(true)
   })
 
+  test("mergeOptimisticPage uses IDs only to break equal-time ties", () => {
+    const sessionID = "ses_1"
+    const page = mergeOptimisticPage(
+      {
+        session: [userMessage("msg_z", sessionID, 1)],
+        part: [],
+        complete: true,
+      },
+      [{ message: userMessage("msg_a", sessionID, 1), parts: [] }],
+    )
+
+    expect(page.session.map((message) => message.id)).toEqual(["msg_a", "msg_z"])
+  })
+
   test("mergeOptimisticPage keeps missing optimistic parts until the server has them", () => {
     const sessionID = "ses_1"
     const page = mergeOptimisticPage(
diff --git a/packages/app/src/context/sync.tsx b/packages/app/src/context/sync.tsx
index b90f49ffd49..7dbf66eb736 100644
--- a/packages/app/src/context/sync.tsx
+++ b/packages/app/src/context/sync.tsx
@@ -3,6 +3,7 @@ import { createMemo } from "solid-js"
 import { useServerSync } from "./server-sync"
 import { useSDK } from "./sdk"
 import type { Message, Part } from "@opencode-ai/sdk/v2/client"
+import { messageKey } from "@/utils/session-message"
 
 const SKIP_PARTS = new Set(["patch", "step-start", "step-finish"])
 
@@ -67,7 +68,7 @@ export function mergeOptimisticPage(page: MessagePage, items: OptimisticItem[])
   const confirmed: string[] = []
 
   for (const item of items) {
-    const result = Binary.search(session, item.message.id, (message) => message.id)
+    const result = Binary.search(session, messageKey(item.message), messageKey)
     const found = result.found
     if (!found) session.splice(result.index, 0, item.message)
 
@@ -92,7 +93,7 @@ export function mergeOptimisticPage(page: MessagePage, items: OptimisticItem[])
 export function applyOptimisticAdd(draft: OptimisticStore, input: OptimisticAddInput) {
   const messages = draft.message[input.sessionID]
   if (messages) {
-    const result = Binary.search(messages, input.message.id, (m) => m.id)
+    const result = Binary.search(messages, messageKey(input.message), messageKey)
     messages.splice(result.index, 0, input.message)
   } else {
     draft.message[input.sessionID] = [input.message]
@@ -103,8 +104,8 @@ export function applyOptimisticAdd(draft: OptimisticStore, input: OptimisticAddI
 export function applyOptimisticRemove(draft: OptimisticStore, input: OptimisticRemoveInput) {
   const messages = draft.message[input.sessionID]
   if (messages) {
-    const result = Binary.search(messages, input.messageID, (m) => m.id)
-    if (result.found) messages.splice(result.index, 1)
+    const index = messages.findIndex((message) => message.id === input.messageID)
+    if (index >= 0) messages.splice(index, 1)
   }
   delete draft.part[input.messageID]
 }
diff --git a/packages/app/src/utils/session-message.ts b/packages/app/src/utils/session-message.ts
index 93d86a66bb2..eef9f4e6dfb 100644
--- a/packages/app/src/utils/session-message.ts
+++ b/packages/app/src/utils/session-message.ts
@@ -12,6 +12,14 @@ const emptyTokens = { input: 0, output: 0, reasoning: 0, cache: { read: 0, write
 const emptyModel: { id: string; providerID: string; variant?: string } = { id: "", providerID: "" }
 const decodeToolInput = Schema.decodeUnknownOption(Schema.UnknownFromJsonString)
 
+export function compareMessages(a: Pick<Message, "id" | "time">, b: Pick<Message, "id" | "time">) {
+  const left = messageKey(a)
+  const right = messageKey(b)
+  return left < right ? -1 : left > right ? 1 : 0
+}
+
+export const messageKey = (message: Pick<Message, "id" | "time">) => message.time.created + message.id
+
 function record(value: unknown): value is Record<string, unknown> {
   return !!value && typeof value === "object" && !Array.isArray(value)
 }