fix(server): transport result.answer carries the last segment, reset set aligned with the stream layer

packages/webui/acp.mjs

@@ -251,20 +251,44 @@ export class McodeAcpClient extends EventEmitter {
       //   （含截图工具的 base64 rawOutput）都被 push 进数组且无任何消费者，
       //   自迭代长任务把堆撑到 GB 级直到 heap OOM。thinking/answer 累积
       //   保留（finalize 有消费者）。
-      const result = { thinking: '', answer: '', messageIds: new Set(), stopReason: null }
+      // session-isolation/07: thinking/answer are PER-SEGMENT, not
+      //   turn-long. The discriminator mirrors streamAcpPrompt's
+      //   lastChunkKind (session-isolation/06): chunks of the same kind
+      //   append (streaming growth), a kind change resets — so
+      //   result.answer / result.thinking carry the LAST segment when
+      //   the prompt settles, the same value the live `●` / `▲` lines
+      //   hold. The old turn-long concatenation leaked into the [send]
+      //   result log, the ● finalize rewrite, the no-usage token
+      //   estimate and the empty-turn note.
+      const result = { thinking: '', answer: '', messageIds: new Set(), stopReason: null, lastChunkKind: null }
       const onUpdate = (u) => {
         if (u.sessionUpdate === 'agent_thought_chunk' && u.content?.type === 'text') {
+          if (result.lastChunkKind !== 'thought') result.thinking = ''
           result.thinking += u.content.text
+          result.lastChunkKind = 'thought'
           if (u.messageId) result.messageIds.add(u.messageId)
           try { onChunk?.({ kind: 'thought', text: u.content.text }) } catch {}
         } else if (u.sessionUpdate === 'agent_message_chunk' && u.content?.type === 'text') {
+          if (result.lastChunkKind !== 'message') result.answer = ''
           result.answer += u.content.text
+          result.lastChunkKind = 'message'
           if (u.messageId) result.messageIds.add(u.messageId)
           try { onChunk?.({ kind: 'message', text: u.content.text }) } catch {}
         } else if (u.sessionUpdate === 'tool_call') {
+          // session-isolation/07 (acceptance alignment): ONLY
+          // chat-line-breaking tool events reset the per-segment
+          // accumulator — the same rule as streamAcpPrompt's
+          // lastChunkKind (server/lib/mcode-acp.js; keep the two in
+          // sync). Non-rendering events (usage_update, plan_update,
+          // session_info_update, mode/goal/config updates) can
+          // interleave MID-segment and must NOT reset: an early reset
+          // would truncate result.answer before streamAcpPrompt's
+          // settle merge consumes it.
+          result.lastChunkKind = 'tool_call'
           // payload: {toolCallId, title, name, status, rawInput, ...}
           try { onChunk?.({ kind: 'tool_call', update: u }) } catch {}
         } else if (u.sessionUpdate === 'tool_call_update') {
+          result.lastChunkKind = 'tool_call_update'
           try { onChunk?.({ kind: 'tool_update', update: u }) } catch {}
         } else if (u.sessionUpdate === 'usage_update') {
           // payload: {used, size, cost} — cumulative values for the

packages/webui/server/lib/mcode-acp.js

@@ -885,6 +885,12 @@ function streamAcpPrompt(
           // plan_update, error, anything else) breaks the same-prefix
           // chain. Without this update, the next message chunk would
           // see lastChunkKind === "message" and skip the reset.
+          // session-isolation/07: this reset set is the canonical one —
+          // keep acp.mjs#prompt's result.lastChunkKind in sync (only
+          // chat-line-breaking tool events reset there; usage / plan /
+          // session_info events must NOT, they can interleave
+          // MID-segment and an early reset would truncate
+          // result.answer).
           r.lastChunkKind = "tool_call";
         } else if (c.kind === "tool_update" && c.update) {
           applyToolUpdate(r, cs, c.update);
@@ -968,6 +974,15 @@ function streamAcpPrompt(
         pushStateFor(cid);
       })
       .then((result) => {
+        // session-isolation/07: the transport's result.answer/thinking
+        // carry the LAST segment (per-segment discriminator in acp.mjs,
+        // mirroring this callback's lastChunkKind resets) — not a
+        // turn-long concatenation. `|| r.answer` keeps the
+        // callback-derived value when the transport saw no chunks of
+        // that kind; both sides now agree on the same segment
+        // semantics, so the empty-turn note, the no-usage token
+        // estimate, the ● finalize rewrite and the [send] result log
+        // all read the final segment.
         r.answer = result.answer || r.answer;
         r.thinking = result.thinking || r.thinking;
         r.stopReason = result.stopReason;