fix(core): enforce one step settlement

packages/schema/src/session-event.ts

@@ -165,7 +165,7 @@ export namespace Step {
     schema: {
       ...Base,
       assistantMessageID: SessionMessage.ID,
-      finish: Schema.String,
+      finish: SessionMessage.Finish,
       cost: Schema.Finite,
       tokens: Schema.Struct({
         input: Schema.Finite,
@@ -195,7 +195,7 @@ export namespace Step {
 
   export const Interrupted = Event.define({
     type: "session.next.step.interrupted",
-    ...options,
+    ...stepSettlementOptions,
     schema: {
       ...Base,
       assistantMessageID: SessionMessage.ID,

packages/schema/src/session-message.ts

@@ -21,6 +21,17 @@ export const UnknownError = Schema.Struct({
   message: Schema.String,
 }).annotate({ identifier: "Session.Error.Unknown" })
 
+export const Finish = Schema.Literals([
+  "stop",
+  "length",
+  "tool-calls",
+  "content-filter",
+  "error",
+  "unknown",
+  "interrupted",
+])
+export type Finish = typeof Finish.Type
+
 const Base = {
   id: ID,
   metadata: Schema.Record(Schema.String, Schema.Unknown).pipe(optional),
@@ -169,7 +180,7 @@ export const Assistant = Schema.Struct({
     end: Schema.String.pipe(optional),
     files: Schema.Array(RelativePath).pipe(optional),
   }).pipe(optional),
-  finish: Schema.String.pipe(optional),
+  finish: Finish.pipe(optional),
   cost: Schema.Finite.pipe(optional),
   tokens: Schema.Struct({
     input: Schema.Finite,

packages/schema/test/event-manifest.test.ts

@@ -42,11 +42,14 @@ describe("public event manifest", () => {
     expect(Reference.Event.Definitions).toEqual([Reference.Event.Updated])
     expect(EventManifest.Latest.has("ide.installed")).toBe(false)
     expect(IdeEvent.Definitions).toEqual([IdeEvent.Installed])
-    expect(EventManifest.Definitions.slice(44, 47)).toEqual([
+    const partDelta = EventManifest.Definitions.indexOf(SessionV1.Event.PartDelta)
+    expect(partDelta).toBeGreaterThanOrEqual(0)
+    expect(EventManifest.Definitions.slice(partDelta, partDelta + 3)).toEqual([
       SessionV1.Event.PartDelta,
       SessionV1.Event.Diff,
       SessionV1.Event.Error,
     ])
+    expect(EventManifest.Latest.get("session.next.step.interrupted")).toBe(SessionEvent.Step.Interrupted)
     expect(EventManifest.Durable.has("session.next.step.ended.1")).toBe(false)
     expect(EventManifest.Durable.get("session.next.step.ended.2")).toBe(SessionEvent.Step.Ended)
   })