diff --git a/packages/opencode/src/cli/cmd/debug/agent.handler.ts b/packages/opencode/src/cli/cmd/debug/agent.handler.ts
index b9d9ff49c8e4..2706a868d9bc 100644
--- a/packages/opencode/src/cli/cmd/debug/agent.handler.ts
+++ b/packages/opencode/src/cli/cmd/debug/agent.handler.ts
@@ -8,6 +8,7 @@ import { Provider } from "@/provider/provider"
 import { Session } from "@/session/session"
 import type { MessageV2 } from "../../../session/message-v2"
 import { MessageID, PartID } from "../../../session/schema"
+import { Identifier } from "@/id/id"
 import { ToolRegistry } from "@/tool/registry"
 import { Permission } from "../../../permission"
 import { iife } from "../../../util/iife"
@@ -129,7 +130,6 @@ const createToolContext = Effect.fn("Cli.debug.agent.createToolContext")(functio
 ) {
   const sessionSvc = yield* Session.Service
   const session = yield* sessionSvc.create({ title: `Debug tool run (${agent.name})` })
-  const messageID = MessageID.ascending()
   const model = agent.model
     ? agent.model
     : yield* Effect.gen(function* () {
@@ -149,12 +149,13 @@ const createToolContext = Effect.fn("Cli.debug.agent.createToolContext")(functio
           }),
         )
       })
-  const now = Date.now()
+  const created = Date.now()
+  const messageID = MessageID.ascending(Identifier.create("msg", "ascending", created))
   const message: SessionV1.Assistant = {
     id: messageID,
     sessionID: session.id,
     role: "assistant",
-    time: { created: now },
+    time: { created },
     parentID: messageID,
     modelID: model.modelID,
     providerID: model.providerID,
diff --git a/packages/opencode/src/cli/cmd/github.handler.ts b/packages/opencode/src/cli/cmd/github.handler.ts
index fcf44279ce7f..2266468e289b 100644
--- a/packages/opencode/src/cli/cmd/github.handler.ts
+++ b/packages/opencode/src/cli/cmd/github.handler.ts
@@ -22,7 +22,7 @@ import { InstanceRef } from "@/effect/instance-ref"
 import { SessionShare } from "@/share/session"
 import { Session } from "@/session/session"
 import type { SessionID } from "../../session/schema"
-import { MessageID, PartID } from "../../session/schema"
+import { PartID } from "../../session/schema"
 import { Provider } from "@/provider/provider"
 import { MessageV2 } from "../../session/message-v2"
 import { EventV2Bridge } from "@/event-v2-bridge"
@@ -902,7 +902,6 @@ export const githubRun = Effect.fn("Cli.github.run")(function* (args: { event?:
           const prompt = sessionPrompt
           const result = yield* prompt.prompt({
             sessionID: session.id,
-            messageID: MessageID.ascending(),
             variant,
             model: {
               providerID,
@@ -950,7 +949,6 @@ export const githubRun = Effect.fn("Cli.github.run")(function* (args: { event?:
           console.log("Requesting summary from agent...")
           const summary = yield* prompt.prompt({
             sessionID: session.id,
-            messageID: MessageID.ascending(),
             variant,
             model: {
               providerID,
diff --git a/packages/opencode/src/session/compaction.ts b/packages/opencode/src/session/compaction.ts
index 75d6374bfa54..187310ffa3c0 100644
--- a/packages/opencode/src/session/compaction.ts
+++ b/packages/opencode/src/session/compaction.ts
@@ -3,6 +3,7 @@ import { SessionV1 } from "@opencode-ai/core/v1/session"
 import { ConfigV1 } from "@opencode-ai/core/v1/config/config"
 import { Session } from "./session"
 import { SessionID, MessageID, PartID } from "./schema"
+import { Identifier } from "@/id/id"
 import { Provider } from "@/provider/provider"
 import { MessageV2 } from "./message-v2"
 import { Token } from "@/util/token"
@@ -390,8 +391,9 @@ const layer = Layer.effect(
           .filter(Boolean)
           .join("\n\n")
       const ctx = yield* InstanceState.context
+      const created = Date.now()
       const msg: SessionV1.Assistant = {
-        id: MessageID.ascending(),
+        id: MessageID.ascending(Identifier.create("msg", "ascending", created)),
         role: "assistant",
         parentID: input.parentID,
         sessionID: input.sessionID,
@@ -412,9 +414,7 @@ const layer = Layer.effect(
         },
         modelID: model.id,
         providerID: model.providerID,
-        time: {
-          created: Date.now(),
-        },
+        time: { created },
       }
       yield* session.updateMessage(msg)
       const processor = yield* processors.create({
@@ -468,11 +468,12 @@ const layer = Layer.effect(
       if (result === "continue" && input.auto) {
         if (replay) {
           const original = replay.info
+          const created = Date.now()
           const replayMsg = yield* session.updateMessage({
-            id: MessageID.ascending(),
+            id: MessageID.ascending(Identifier.create("msg", "ascending", created)),
             role: "user",
             sessionID: input.sessionID,
-            time: { created: Date.now() },
+            time: { created },
             agent: original.agent,
             model: original.model,
             format: original.format,
@@ -516,11 +517,12 @@ const layer = Layer.effect(
               { enabled: true },
             )).enabled
           ) {
+            const created = Date.now()
             const continueMsg = yield* session.updateMessage({
-              id: MessageID.ascending(),
+              id: MessageID.ascending(Identifier.create("msg", "ascending", created)),
               role: "user",
               sessionID: input.sessionID,
-              time: { created: Date.now() },
+              time: { created },
               agent: userMessage.agent,
               model: userMessage.model,
             })
@@ -563,13 +565,14 @@ const layer = Layer.effect(
       auto: boolean
       overflow?: boolean
     }) {
+      const created = Date.now()
       const msg = yield* session.updateMessage({
-        id: MessageID.ascending(),
+        id: MessageID.ascending(Identifier.create("msg", "ascending", created)),
         role: "user",
         model: input.model,
         sessionID: input.sessionID,
         agent: input.agent,
-        time: { created: Date.now() },
+        time: { created },
       })
       yield* session.updatePart({
         id: PartID.ascending(),
diff --git a/packages/opencode/src/session/prompt.ts b/packages/opencode/src/session/prompt.ts
index 0f85d44f209b..5fd599e09f5a 100644
--- a/packages/opencode/src/session/prompt.ts
+++ b/packages/opencode/src/session/prompt.ts
@@ -4,6 +4,7 @@ import path from "path"
 import { SessionV1 } from "@opencode-ai/core/v1/session"
 import os from "os"
 import { SessionID, MessageID, PartID } from "./schema"
+import { Identifier } from "@/id/id"
 import { MessageV2 } from "./message-v2"
 import { SessionRevert } from "./revert"
 import { Session } from "./session"
@@ -265,8 +266,9 @@ const layer = Layer.effect(
       const promptOps = yield* ops()
       const { task: taskTool } = yield* registry.named()
       const taskModel = task.model ? yield* getModel(task.model.providerID, task.model.modelID, sessionID) : model
+      const created = Date.now()
       const assistantMessage: SessionV1.Assistant = yield* sessions.updateMessage({
-        id: MessageID.ascending(),
+        id: MessageID.ascending(Identifier.create("msg", "ascending", created)),
         role: "assistant",
         parentID: lastUser.id,
         sessionID,
@@ -278,7 +280,7 @@ const layer = Layer.effect(
         tokens: { input: 0, output: 0, reasoning: 0, cache: { read: 0, write: 0 } },
         modelID: taskModel.id,
         providerID: taskModel.providerID,
-        time: { created: Date.now() },
+        time: { created },
       })
       let part: SessionV1.ToolPart = yield* sessions.updatePart({
         id: PartID.ascending(),
@@ -429,11 +431,12 @@ const layer = Layer.effect(
 
       if (!task.command) return
 
+      const summaryCreated = Date.now()
       const summaryUserMsg: SessionV1.User = {
-        id: MessageID.ascending(),
+        id: MessageID.ascending(Identifier.create("msg", "ascending", summaryCreated)),
         sessionID,
         role: "user",
-        time: { created: Date.now() },
+        time: { created: summaryCreated },
         agent: lastUser.agent,
         model: lastUser.model,
       }
@@ -467,10 +470,11 @@ const layer = Layer.effect(
               throw error
             }
             const model = input.model ?? agent.model ?? (yield* currentModel(input.sessionID))
+            const userCreated = Date.now()
             const userMsg: SessionV1.User = {
-              id: input.messageID ?? MessageID.ascending(),
+              id: input.messageID ?? MessageID.ascending(Identifier.create("msg", "ascending", userCreated)),
               sessionID: input.sessionID,
-              time: { created: Date.now() },
+              time: { created: userCreated },
               role: "user",
               agent: input.agent,
               model: { providerID: model.providerID, modelID: model.modelID },
@@ -486,15 +490,16 @@ const layer = Layer.effect(
             }
             yield* sessions.updatePart(userPart)
 
+            const assistantCreated = Date.now()
             const msg: SessionV1.Assistant = {
-              id: MessageID.ascending(),
+              id: MessageID.ascending(Identifier.create("msg", "ascending", assistantCreated)),
               sessionID: input.sessionID,
               parentID: userMsg.id,
               mode: input.agent,
               agent: input.agent,
               cost: 0,
               path: { cwd: ctx.directory, root: ctx.worktree },
-              time: { created: Date.now() },
+              time: { created: assistantCreated },
               role: "assistant",
               tokens: { input: 0, output: 0, reasoning: 0, cache: { read: 0, write: 0 } },
               modelID: model.modelID,
@@ -653,11 +658,12 @@ const layer = Layer.effect(
           : undefined
       const variant = input.variant ?? (ag.variant && full?.variants?.[ag.variant] ? ag.variant : undefined)
 
+      const created = Date.now()
       const info: SessionV1.User = {
-        id: input.messageID ?? MessageID.ascending(),
+        id: input.messageID ?? MessageID.ascending(Identifier.create("msg", "ascending", created)),
         role: "user",
         sessionID: input.sessionID,
-        time: { created: Date.now() },
+        time: { created },
         tools: input.tools,
         agent: ag.name,
         model: {
@@ -1183,8 +1189,9 @@ const layer = Layer.effect(
             Effect.provideService(Session.Service, sessions),
           )
 
+          const created = Date.now()
           const msg: SessionV1.Assistant = {
-            id: MessageID.ascending(),
+            id: MessageID.ascending(Identifier.create("msg", "ascending", created)),
             parentID: lastUser.id,
             role: "assistant",
             mode: agent.name,
@@ -1195,7 +1202,7 @@ const layer = Layer.effect(
             tokens: { input: 0, output: 0, reasoning: 0, cache: { read: 0, write: 0 } },
             modelID: model.id,
             providerID: model.providerID,
-            time: { created: Date.now() },
+            time: { created },
             sessionID,
           }
           yield* sessions.updateMessage(msg)
diff --git a/packages/opencode/src/tool/plan.ts b/packages/opencode/src/tool/plan.ts
index 3b5ed978545a..397d213176e8 100644
--- a/packages/opencode/src/tool/plan.ts
+++ b/packages/opencode/src/tool/plan.ts
@@ -7,6 +7,7 @@ import { Session } from "@/session/session"
 import { MessageV2 } from "../session/message-v2"
 import { Provider } from "@/provider/provider"
 import { InstanceState } from "@/effect/instance-state"
+import { Identifier } from "@/id/id"
 import { MessageID, PartID } from "../session/schema"
 import EXIT_DESCRIPTION from "./plan-exit.txt"
 
@@ -50,11 +51,12 @@ export const PlanExitTool = Tool.define(
           const model =
             lastUser?.info.role === "user" && lastUser.info.model ? lastUser.info.model : yield* provider.defaultModel()
 
+          const created = Date.now()
           const msg: SessionV1.User = {
-            id: MessageID.ascending(),
+            id: MessageID.ascending(Identifier.create("msg", "ascending", created)),
             sessionID: ctx.sessionID,
             role: "user",
-            time: { created: Date.now() },
+            time: { created },
             agent: "build",
             model,
           }
diff --git a/packages/opencode/src/tool/task.ts b/packages/opencode/src/tool/task.ts
index d8ca640cfba9..83b7e0616122 100644
--- a/packages/opencode/src/tool/task.ts
+++ b/packages/opencode/src/tool/task.ts
@@ -4,7 +4,7 @@ import { ToolJsonSchema } from "./json-schema"
 import { SessionV1 } from "@opencode-ai/core/v1/session"
 import { BackgroundJob } from "@/background/job"
 import { Session } from "@/session/session"
-import { SessionID, MessageID } from "../session/schema"
+import { SessionID } from "../session/schema"
 import { MessageV2 } from "../session/message-v2"
 import { Agent } from "../agent/agent"
 import { deriveSubagentSessionPermission } from "../agent/subagent-permissions"
@@ -200,7 +200,6 @@ export const TaskTool = Tool.define(
       const runTask = Effect.fn("TaskTool.runTask")(function* () {
         const parts = yield* ops.resolvePromptParts(params.prompt)
         const result = yield* ops.prompt({
-          messageID: MessageID.ascending(),
           sessionID: nextSession.id,
           model: {
             modelID: model.modelID,
diff --git a/packages/opencode/test/session/prompt.test.ts b/packages/opencode/test/session/prompt.test.ts
index da6e0f8d036f..fbc405363d66 100644
--- a/packages/opencode/test/session/prompt.test.ts
+++ b/packages/opencode/test/session/prompt.test.ts
@@ -5,6 +5,7 @@ import { LayerNode } from "@opencode-ai/core/effect/layer-node"
 import { SessionProjector } from "@opencode-ai/core/session/projector"
 import { eq } from "drizzle-orm"
 import { EventV2Bridge } from "@/event-v2-bridge"
+import { Identifier } from "@/id/id"
 import { expect } from "bun:test"
 import { Cause, Deferred, Duration, Effect, Exit, Fiber, Layer } from "effect"
 import path from "path"
@@ -442,6 +443,34 @@ const boot = Effect.fn("test.boot")(function* (input?: { title?: string }) {
   return { prompt, run, sessions, chat }
 })
 
+it.instance("prompt persists the timestamp embedded in its freshly minted message ID", () =>
+  Effect.acquireUseRelease(
+    Effect.sync(() => {
+      const original = Date.now
+      let reads = 0
+      Date.now = () => 1_000 + reads++
+      return original
+    }),
+    () =>
+      Effect.gen(function* () {
+        const { prompt, chat } = yield* boot()
+        const message = yield* prompt.prompt({
+          sessionID: chat.id,
+          agent: "build",
+          model: ref,
+          noReply: true,
+          parts: [{ type: "text", text: "timestamp invariant" }],
+        })
+
+        expect(Identifier.timestamp(message.info.id)).toBe(message.info.time.created)
+      }),
+    (original) =>
+      Effect.sync(() => {
+        Date.now = original
+      }),
+  ),
+)
+
 // Loop semantics
 
 noLLMServer.instance(