feat(session): define explicit fork boundaries

packages/schema/src/session-event.ts

@@ -22,6 +22,7 @@ import { Snapshot } from "./snapshot.js"
 import { TokenUsage } from "./token-usage.js"
 import { SessionPending } from "./session-pending.js"
 import { Project } from "./project.js"
+import { SessionFork } from "./session-fork.js"
 
 export { FileAttachment }
 
@@ -127,8 +128,8 @@ export const Forked = Event.durable({
   schema: {
     ...Base,
     parentID: SessionID,
-    parentSeq: Schema.Int.check(Schema.isGreaterThanOrEqualTo(-1)),
-    from: SessionMessage.ID.pipe(optional),
+    boundary: SessionFork.Boundary,
+    instructions: Instruction.Values.pipe(optional),
   },
 })
 export type Forked = typeof Forked.Type

packages/schema/src/session-fork.ts

@@ -0,0 +1,16 @@
+export * as SessionFork from "./session-fork.js"
+
+import { Schema } from "effect"
+import { SessionMessage } from "./session-message.js"
+
+export const Boundary = Schema.Union([
+  Schema.Struct({ type: Schema.Literal("before"), messageID: SessionMessage.ID }),
+  Schema.Struct({ type: Schema.Literal("through"), messageID: SessionMessage.ID }),
+]).annotate({ identifier: "Session.ForkBoundary" })
+export type Boundary = typeof Boundary.Type
+
+export const RequestBoundary = Schema.Union([
+  Schema.Struct({ type: Schema.Literal("before"), messageID: SessionMessage.ID }),
+  Schema.Struct({ type: Schema.Literal("through") }),
+]).annotate({ identifier: "Session.ForkRequestBoundary" })
+export type RequestBoundary = typeof RequestBoundary.Type

packages/schema/src/session.ts

@@ -8,10 +8,10 @@ import { Project } from "./project.js"
 import { DateTimeUtcFromMillis, optional, RelativePath } from "./schema.js"
 import { SessionEvent } from "./session-event.js"
 import { SessionID } from "./session-id.js"
-import { SessionMessage } from "./session-message.js"
 import { Money } from "./money.js"
 import { TokenUsage } from "./token-usage.js"
 import { Revert } from "./session-revert.js"
+import { SessionFork } from "./session-fork.js"
 
 export const ID = SessionID
 export type ID = SessionID
@@ -19,6 +19,10 @@ export type ID = SessionID
 export const Event = SessionEvent
 
 export { Revert }
+export const ForkBoundary = SessionFork.Boundary
+export type ForkBoundary = SessionFork.Boundary
+export const ForkRequestBoundary = SessionFork.RequestBoundary
+export type ForkRequestBoundary = SessionFork.RequestBoundary
 
 export interface Info extends Schema.Schema.Type<typeof Info> {}
 export const Info = Schema.Struct({
@@ -26,8 +30,7 @@ export const Info = Schema.Struct({
   parentID: ID.pipe(optional),
   fork: Schema.Struct({
     sessionID: ID,
-    /** Messages before this exclusive boundary are copied into the fork. */
-    messageID: SessionMessage.ID.pipe(optional),
+    boundary: ForkBoundary,
   }).pipe(optional),
   projectID: Project.ID,
   agent: Agent.ID.pipe(optional),