fix(core): separate interruption from finish

packages/schema/test/session-message.test.ts

@@ -0,0 +1,22 @@
+import { expect, test } from "bun:test"
+import { Schema } from "effect"
+import { SessionMessage } from "../src/session-message"
+
+test("does not model interruption as a provider finish reason", () => {
+  expect(() => Schema.decodeUnknownSync(SessionMessage.Finish)("interrupted")).toThrow()
+  expect(Schema.decodeUnknownSync(SessionMessage.Finish)("error")).toBe("error")
+})
+
+test("decodes projected assistant histories with arbitrary finish strings", () => {
+  const message = Schema.decodeUnknownSync(SessionMessage.Message)({
+    id: "msg_legacy",
+    type: "assistant",
+    agent: "build",
+    model: { id: "model", providerID: "provider" },
+    content: [],
+    finish: "legacy-provider-reason",
+    time: { created: 0, completed: 1 },
+  })
+
+  expect(message).toMatchObject({ type: "assistant", finish: "legacy-provider-reason" })
+})