refactor: identify and freeze messages at creation

packages/client/runtime/tests/event-script.ts

@@ -1,3 +1,4 @@
+import { createUserMessage, createMessage, createToolResultMessage, CallId } from '@deepseek-ai/dsh-llm'
 // Minimal SessionEvent builders for orchestration tests (shape mirrors what the
 // host emits; only the fields the object layer reads).
 import type { ContentBlock } from '@deepseek-ai/dsh-llm/types'
@@ -13,7 +14,9 @@ export const ev = {
   turnStart: (seq: number, turn: number): SessionEvent =>
     at(seq, { type: 'turn/start', data: { turn, trigger: { kind: 'message', source: { kind: 'user' } } } }),
   user: (seq: number, body: string): SessionEvent =>
-    at(seq, { type: 'user/message', surfaceOp: 'append', data: { content: text(body), source: { kind: 'user' } } }),
+    at(seq, { type: 'user/message', surfaceOp: 'append', data: createUserMessage({
+      content: text(body), source: { kind: 'user' },
+    }) }),
   stepStart: (seq: number, turn: number, step = 0): SessionEvent =>
     at(seq, { type: 'step/start', data: { turn, step } }),
   chunkStart: (seq: number, turn: number, step = 0, index = 0): SessionEvent =>
@@ -21,11 +24,33 @@ export const ev = {
   chunkText: (seq: number, turn: number, piece: string, step = 0, index = 0): SessionEvent =>
     at(seq, { type: 'assistant/chunk', data: { turn, step, chunk: { type: 'text-delta', index, text: piece } } }),
   assistant: (seq: number, turn: number, body: string, step = 0): SessionEvent =>
-    at(seq, { type: 'assistant/message', surfaceOp: 'append', data: { turn, step, content: text(body), provenance: { provider: 'fake', model: 'fk-1' } } }),
+    at(seq, { type: 'assistant/message', surfaceOp: 'append', data: {
+      turn, step,
+      message: createMessage({
+        role: 'assistant',
+        content: text(body),
+        source: {
+          kind: 'model',
+          ...{ provider: 'fake', model: 'fk-1' },
+        },
+      }),
+    } }),
   toolCall: (seq: number, turn: number, callId: string, name: string, args: string, step = 0): SessionEvent =>
     at(seq, { type: 'tool/call', data: { turn, step, callId, name, arguments: args } }),
   toolResult: (seq: number, turn: number, callId: string, body: string, step = 0): SessionEvent =>
-    at(seq, { type: 'tool/result', surfaceOp: 'append', data: { turn, step, callId, content: text(body), isError: false } }),
+    at(seq, {
+      type: 'tool/result',
+      surfaceOp: 'append',
+      data: {
+        turn,
+        step,
+        message: createToolResultMessage({
+          callId: CallId(callId),
+          content: text(body),
+          isError: false,
+        }),
+      },
+    }),
   codeDispatchStart: (seq: number, parentCallId: string, n: number, name: string, args: unknown): SessionEvent =>
     at(seq, {
       type: 'tool/code-dispatch-start',