refactor(core): simplify session fork event

packages/client/src/generated/types.ts

@@ -799,12 +799,7 @@ export type SessionsHistoryOutput = {
           readonly timestamp: number
           readonly sessionID: string
           readonly parentID: string
-          readonly slug: string
-          readonly title: string
-          readonly agent?: string
-          readonly model?: { readonly id: string; readonly providerID: string; readonly variant?: string }
           readonly messageID?: string
-          readonly copiedSeq: number
         }
       }
     | {
@@ -1283,12 +1278,7 @@ export type SessionsEventsOutput =
         readonly timestamp: number
         readonly sessionID: string
         readonly parentID: string
-        readonly slug: string
-        readonly title: string
-        readonly agent?: string
-        readonly model?: { readonly id: string; readonly providerID: string; readonly variant?: string }
         readonly messageID?: string
-        readonly copiedSeq: number
       }
     }
   | {

packages/core/src/session.ts

@@ -298,35 +298,12 @@ export const layer = Layer.effect(
           : undefined
         if (input.messageID && !boundary)
           return yield* new MessageNotFoundError({ sessionID: input.sessionID, messageID: input.messageID })
-        const copied = yield* db
-          .select({ seq: SessionMessageTable.seq })
-          .from(SessionMessageTable)
-          .where(
-            and(
-              eq(SessionMessageTable.session_id, input.sessionID),
-              boundary === undefined ? undefined : lt(SessionMessageTable.seq, boundary.seq),
-            ),
-          )
-          .orderBy(desc(SessionMessageTable.seq))
-          .limit(1)
-          .get()
-          .pipe(Effect.orDie)
         const sessionID = SessionSchema.ID.create()
         yield* events.publish(SessionEvent.Forked, {
           sessionID,
           parentID: parent.id,
-          slug: Slug.create(),
-          title: forkTitle(parent.title),
-          agent: parent.agent,
-          model: parent.model,
           messageID: input.messageID,
-          copiedSeq: copied?.seq ?? 0,
           timestamp: yield* DateTime.now,
-        }, {
-          commit: (seq) =>
-            copied && copied.seq > seq
-              ? EventV2.reserveSequence(db, sessionID, copied.seq)
-              : Effect.void,
         })
         return yield* result.get(sessionID).pipe(Effect.orDie)
       }),
@@ -563,12 +540,6 @@ export const defaultLayer = layer.pipe(
   Layer.orDie,
 )
 
-const forkTitle = (value: string) => {
-  const match = value.match(/^(.+) \(fork #(\d+)\)$/)
-  if (match) return `${match[1]} (fork #${Number.parseInt(match[2], 10) + 1})`
-  return `${value} (fork #1)`
-}
-
 const resolvePrompt = (input: PromptInput.Prompt) =>
   Prompt.make({
     text: input.text,

packages/core/src/session/projector.ts

@@ -15,6 +15,7 @@ import { WorkspaceV2 } from "../workspace"
 import { SessionContextEpoch } from "./context-epoch"
 import { MessageTable, PartTable, SessionInputTable, SessionMessageTable, SessionTable } from "./sql"
 import type { DeepMutable } from "../schema"
+import { Slug } from "../util/slug"
 
 type DatabaseService = Database.Interface["db"]
 type MessageEvent = Exclude<SessionEvent.Event, typeof SessionEvent.Forked.Type>
@@ -41,6 +42,12 @@ const emptyUsage = (): Usage => ({
   tokens: { input: 0, output: 0, reasoning: 0, cache: { read: 0, write: 0 } },
 })
 
+const forkTitle = (value: string) => {
+  const match = value.match(/^(.+) \(fork #(\d+)\)$/)
+  if (match) return `${match[1]} (fork #${Number.parseInt(match[2], 10) + 1})`
+  return `${value} (fork #1)`
+}
+
 function usage(part: (typeof SessionV1.Event.PartUpdated.Type)["data"]["part"] | unknown): Usage | undefined {
   if (typeof part !== "object" || part === null) return undefined
   const value = part as Record<string, unknown>
@@ -144,6 +151,31 @@ const projectFork = Effect.fn("SessionProjector.projectFork")(function* (
     .get()
     .pipe(Effect.orDie)
   if (!parent) return yield* Effect.die(`Fork parent session not found: ${event.data.parentID}`)
+  const boundary = event.data.messageID
+    ? yield* db
+        .select({ seq: SessionMessageTable.seq })
+        .from(SessionMessageTable)
+        .where(
+          and(eq(SessionMessageTable.session_id, event.data.parentID), eq(SessionMessageTable.id, event.data.messageID)),
+        )
+        .get()
+        .pipe(Effect.orDie)
+    : undefined
+  if (event.data.messageID && !boundary) return yield* Effect.die(`Fork boundary message not found: ${event.data.messageID}`)
+  const copied = yield* db
+    .select({ seq: SessionMessageTable.seq })
+    .from(SessionMessageTable)
+    .where(
+      and(
+        eq(SessionMessageTable.session_id, event.data.parentID),
+        boundary === undefined ? undefined : lt(SessionMessageTable.seq, boundary.seq),
+      ),
+    )
+    .orderBy(desc(SessionMessageTable.seq))
+    .limit(1)
+    .get()
+    .pipe(Effect.orDie)
+  const copiedSeq = copied?.seq ?? 0
 
   const stored = yield* db
     .insert(SessionTable)
@@ -152,12 +184,12 @@ const projectFork = Effect.fn("SessionProjector.projectFork")(function* (
       parent_id: event.data.parentID,
       project_id: parent.project_id,
       workspace_id: parent.workspace_id,
-      slug: event.data.slug,
+      slug: Slug.create(),
       directory: parent.directory,
       path: parent.path,
-      title: event.data.title,
+      title: forkTitle(parent.title),
-      agent: event.data.agent,
+      agent: parent.agent,
-      model: event.data.model,
+      model: parent.model,
       version: parent.version,
       cost: 0,
       tokens_input: 0,
@@ -184,7 +216,7 @@ const projectFork = Effect.fn("SessionProjector.projectFork")(function* (
         and(
           eq(SessionMessageTable.session_id, event.data.parentID),
           gt(SessionMessageTable.seq, cursor),
-          event.data.messageID === undefined ? undefined : lt(SessionMessageTable.seq, event.data.copiedSeq + 1),
+          copiedSeq === 0 ? undefined : lt(SessionMessageTable.seq, copiedSeq + 1),
         ),
       )
       .orderBy(asc(SessionMessageTable.seq))
@@ -273,7 +305,7 @@ const projectFork = Effect.fn("SessionProjector.projectFork")(function* (
     .where(eq(SessionTable.id, event.data.sessionID))
     .run()
     .pipe(Effect.orDie)
-  if (event.data.copiedSeq > 0) yield* EventV2.reserveSequence(db, event.data.sessionID, event.data.copiedSeq)
+  if (copiedSeq > 0) yield* EventV2.reserveSequence(db, event.data.sessionID, copiedSeq)
 })
 
 function run(db: DatabaseService, event: MessageEvent) {

packages/core/test/session-create.test.ts

@@ -166,7 +166,7 @@ describe("SessionV2.create", () => {
       expect(history.events[0]).toMatchObject({
         type: "session.next.forked",
         durable: { seq: 0 },
-        data: { sessionID: forked.id, parentID: parent.id, copiedSeq: 3 },
+        data: { sessionID: forked.id, parentID: parent.id },
       })
       expect(yield* SessionInput.find(db, forkContext[0]!.id)).toMatchObject({
         sessionID: forked.id,
@@ -216,7 +216,7 @@ describe("SessionV2.create", () => {
       const history = yield* session.history({ sessionID: forked.id, limit: 10 })
       expect(context).toMatchObject([{ text: "First" }])
       expect(context[0]?.id).not.toBe(first.id)
-      expect(history.events[0]).toMatchObject({ data: { copiedSeq: 2, messageID: second.id } })
+      expect(history.events[0]).toMatchObject({ data: { messageID: second.id } })
     }),
   )
 

packages/schema/src/session-event.ts

@@ -100,12 +100,7 @@ export const Forked = Event.define({
   schema: {
     ...Base,
     parentID: SessionID,
-    slug: Schema.String,
-    title: Schema.String,
-    agent: Schema.String.pipe(optional),
-    model: Model.Ref.pipe(optional),
     messageID: SessionMessage.ID.pipe(optional),
-    copiedSeq: NonNegativeInt,
   },
 })
 export type Forked = typeof Forked.Type