fix(opencode): use chronological message boundaries (#40991)

Co-authored-by: Dax <mail@thdxr.com>

packages/opencode/test/session/revert-compact.test.ts

@@ -35,6 +35,18 @@ const user = Effect.fn("test.user")(function* (sessionID: SessionID, agent = "de
   })
 })
 
+const userAt = Effect.fn("test.userAt")(function* (sessionID: SessionID, id: string, created: number) {
+  const session = yield* Session.Service
+  return yield* session.updateMessage({
+    id: MessageID.make(id),
+    role: "user" as const,
+    sessionID,
+    agent: "default",
+    model: { providerID: ProviderV2.ID.make("openai"), modelID: ModelV2.ID.make("gpt-4") },
+    time: { created },
+  })
+})
+
 const assistant = Effect.fn("test.assistant")(function* (sessionID: SessionID, parentID: MessageID, dir: string) {
   const session = yield* Session.Service
   return yield* session.updateMessage({
@@ -426,6 +438,39 @@ describe("revert + compact workflow", () => {
     ),
   )
 
+  it.live(
+    "reverts chronological suffixes on both sides of mixed message ID ordering",
+    provideTmpdirInstance(
+      () =>
+        Effect.gen(function* () {
+          const session = yield* Session.Service
+          const revert = yield* SessionRevert.Service
+          const ids = ["msg_z9-before", "msg_z1-before-wrap", "msg_a0-after-wrap", "msg_a1-after"]
+
+          const run = Effect.fn("test.mixedIDRevert")(function* (target: number) {
+            const info = yield* session.create({})
+            for (const [index, id] of ids.entries()) {
+              const message = yield* userAt(info.id, id, index + 1)
+              yield* text(info.id, message.id, id)
+            }
+
+            const reverted = yield* revert.revert({
+              sessionID: info.id,
+              messageID: MessageID.make(ids[target]!),
+            })
+            yield* revert.cleanup(reverted)
+            const remaining = yield* session.messages({ sessionID: info.id })
+            yield* session.remove(info.id)
+            return remaining.map((msg) => msg.info.time.created)
+          })
+
+          expect(yield* run(1)).toEqual([1])
+          expect(yield* run(2)).toEqual([1, 2])
+        }),
+      { git: true },
+    ),
+  )
+
   it.live(
     "cleanup is a no-op when session has no revert state",
     provideTmpdirInstance(

packages/opencode/test/session/session.test.ts

@@ -238,6 +238,38 @@ describe("Session", () => {
     }),
   )
 
+  it.instance("forks the chronological prefix across mixed message ID ordering", () =>
+    Effect.gen(function* () {
+      const session = yield* SessionNs.Service
+      const created = yield* Effect.acquireRelease(session.create({}), (info) =>
+        session.remove(info.id).pipe(Effect.ignore),
+      )
+      const ids = ["msg_z9-before", "msg_z1-before-wrap", "msg_a0-after-wrap", "msg_a1-after"]
+      for (const [index, id] of ids.entries()) {
+        yield* session.updateMessage({
+          id: MessageID.make(id),
+          sessionID: created.id,
+          role: "user",
+          time: { created: index + 1 },
+          agent: "user",
+          model: { providerID: "test", modelID: "test" },
+        } as SessionV1.User)
+      }
+
+      const beforeWrap = yield* Effect.acquireRelease(
+        session.fork({ sessionID: created.id, messageID: MessageID.make(ids[1]!) }),
+        (info) => session.remove(info.id).pipe(Effect.ignore),
+      )
+      const afterWrap = yield* Effect.acquireRelease(
+        session.fork({ sessionID: created.id, messageID: MessageID.make(ids[2]!) }),
+        (info) => session.remove(info.id).pipe(Effect.ignore),
+      )
+
+      expect((yield* session.messages({ sessionID: beforeWrap.id })).map((msg) => msg.info.time.created)).toEqual([1])
+      expect((yield* session.messages({ sessionID: afterWrap.id })).map((msg) => msg.info.time.created)).toEqual([1, 2])
+    }),
+  )
+
   it.instance("omits metadata when not provided", () =>
     Effect.gen(function* () {
       const session = yield* SessionNs.Service