fix(ui-trajectory): consume prompt changes once

packages/client/ui-trajectory/src/client/trajectory-snapshot-builder.ts

@@ -46,6 +46,7 @@ function headerFor(
 function applyHeader(
   request: Extract<RequestView, { purpose: 'assistant' }>,
   header: TrajectoryRequestHeaderState | undefined,
+  includeChange: boolean,
 ): Extract<RequestView, { purpose: 'assistant' }> {
   return header === undefined
     ? request
@@ -53,7 +54,7 @@ function applyHeader(
       ...request,
       prompt: header.prompt,
       requestConfig: header.prompt.config,
-      ...(header.change === undefined ? {} : { promptChange: header.change }),
+      ...(includeChange && header.change !== undefined ? { promptChange: header.change } : {}),
     }
 }
 
@@ -150,6 +151,7 @@ export class TrajectorySnapshotBuilder implements ConversationViewBuilder<
     const boundaries: { seq: number; time: number }[] = []
     const turnEndings: { turn: number; time: number; error?: string }[] = []
     const callSchemas = new Map<string, ConversationPromptSnapshot['tools'][number]>()
+    const consumedPromptChanges = new Set<number>()
     let partial: TrajectorySnapshot['partial'] = null
     const runningCalls: TrajectorySnapshot['runningCalls'][number][] = []
 
@@ -163,7 +165,12 @@ export class TrajectorySnapshotBuilder implements ConversationViewBuilder<
         const header = data.request === undefined ? undefined : headerFor(data.request, headers)
         if (data.node !== undefined) finalized.push(withRequestConfig(data.node, header?.prompt))
         if (data.partial !== null) partial = data.partial
-        if (data.request !== undefined) requests.push(applyHeader(data.request, header))
+        if (data.request !== undefined) {
+          const includeChange = header?.change !== undefined
+            && !consumedPromptChanges.has(header.seq)
+          requests.push(applyHeader(data.request, header, includeChange))
+          if (includeChange) consumedPromptChanges.add(header.seq)
+        }
         continue
       }
       if (data.kind === 'tool') {

packages/client/ui-trajectory/tests/snapshot-builder.spec.ts

@@ -0,0 +1,62 @@
+import { describe, expect, it } from 'vitest'
+import type { RequestView } from '@deepseek-ai/dsh-client-runtime/client'
+import type { TrajectoryConversationViewNode } from '../src/client/trajectory-contract.ts'
+import { TrajectorySnapshotBuilder } from '../src/client/trajectory-snapshot-builder.ts'
+
+function assistantRequest(startSeq: number, step: number): Extract<RequestView, { purpose: 'assistant' }> {
+  return {
+    purpose: 'assistant',
+    startSeq,
+    turn: 1,
+    step,
+    startedAt: startSeq,
+    completedAt: startSeq + 1,
+    status: 'complete',
+  }
+}
+
+describe('TrajectorySnapshotBuilder', () => {
+  it('inherits one request header across requests without repeating its prompt change', () => {
+    const prompt = {
+      config: { provider: 'test', model: 'test' },
+      system: 'one initial prompt',
+      tools: [],
+    }
+    const nodes: TrajectoryConversationViewNode[] = [
+      {
+        key: 'header',
+        kind: 'trajectory-request-header',
+        id: '2',
+        target: 'trajectory',
+        anchorSeq: 2,
+        data: {
+          kind: 'request-header',
+          header: {
+            seq: 2,
+            time: 2,
+            prompt,
+            change: { seq: 2, time: 2, kind: 'initial' },
+            location: { kind: 'session' },
+          },
+        },
+      },
+      ...[assistantRequest(3, 1), assistantRequest(5, 2)].map(request => ({
+        key: `assistant:${request.step}`,
+        kind: 'trajectory-assistant-step',
+        id: `1:${request.step}`,
+        target: 'trajectory' as const,
+        anchorSeq: request.startSeq,
+        data: { kind: 'assistant' as const, partial: null, request },
+      })),
+    ]
+
+    const snapshot = new TrajectorySnapshotBuilder().replace({ nodes })
+
+    expect(snapshot.requests.map(request => request.purpose === 'assistant'
+      ? request.prompt?.system
+      : undefined)).toEqual(['one initial prompt', 'one initial prompt'])
+    expect(snapshot.requests.map(request => request.purpose === 'assistant'
+      ? request.promptChange?.kind
+      : undefined)).toEqual(['initial', undefined])
+  })
+})