fix(workspace-context): restore baseline after compaction

examples/acp-agent/tests/fixtures/workspace-context-compaction.ts

@@ -0,0 +1,26 @@
+import type { Context } from 'cordis'
+import type {} from '@deepseek-ai/dsh-agent'
+import { COMPACT_CHECKPOINT_SOURCE } from '@deepseek-ai/dsh-compact'
+import { createUserMessage } from '@deepseek-ai/dsh-llm'
+
+export const name = 'workspace-context-compaction'
+
+/** Replace the visible workspace baseline before the snapshot's second step. */
+export function apply(ctx: Context): void {
+  ctx.on('agent/step', (agent, turn, step) => {
+    if (turn !== 1 || step !== 2) return
+    const baseline = agent.session.surface.nodes
+      .map(seq => agent.session.events[seq])
+      .find(event => event?.type === 'user/message'
+        && event.data.source.kind === 'workspace-instructions'
+        && event.data.source.baseline === true)
+    if (baseline === undefined) throw new Error('workspace baseline missing before snapshot compaction')
+    agent.session.append('user/message', createUserMessage({
+      content: [{ type: 'text', text: 'Earlier context was compacted for this snapshot.' }],
+      source: COMPACT_CHECKPOINT_SOURCE,
+    }), {
+      surfaceOp: { op: 'replace', start: baseline.seq, end: baseline.seq },
+      sourceEventSeqs: [baseline.seq],
+    })
+  })
+}