Fix assistant history text block merging

packages/agents-runtime/src/pi-adapter.ts

@@ -107,11 +107,13 @@ export function toAgentHistory(
 
       case `assistant`: {
         const prev = lastAssistant()
-        if (prev) {
-          ;(prev.content as Array<unknown>).push({
-            type: `text`,
-            text: message.content,
-          })
+        const prevContent = prev?.content as
+          | Array<{ type: string; text?: string }>
+          | undefined
+        const lastBlock = prevContent?.[prevContent.length - 1]
+
+        if (lastBlock?.type === `text`) {
+          lastBlock.text = `${lastBlock.text ?? ``}${message.content}`
         } else {
           history.push({
             role: `assistant`,

packages/agents-runtime/test/pi-adapter.test.ts

@@ -417,6 +417,23 @@ describe(`toAgentHistory`, () => {
     expect(second?.role).toBe(`assistant`)
   })
 
+  it(`merges adjacent assistant text messages into one text block`, () => {
+    const messages: Array<LLMMessage> = [
+      { role: `user`, content: `Question` },
+      { role: `assistant`, content: `First chunk.` },
+      { role: `assistant`, content: ` Second chunk.` },
+    ]
+
+    const history = toAgentHistory(messages)
+
+    expect(history).toHaveLength(2)
+    const assistant = history[1] as AssistantMessage
+    expect(assistant.role).toBe(`assistant`)
+    expect(assistant.content).toEqual([
+      { type: `text`, text: `First chunk. Second chunk.` },
+    ])
+  })
+
   it(`merges assistant text and tool_call into a single assistant message`, () => {
     const messages: Array<LLMMessage> = [
       { role: `user`, content: `Help me` },