[codex] 优化输入后的 AI 处理中状态反馈

[utopiafar]

背景

Fixes #136。

输入卡片后，当前首页会先关闭输入面板，但时间线会被全屏 loading 遮住，直到本地提交链路完成后才出现 processing 卡片或 AI activity 状态。这个路径里包含本地持久化、任务入队、定位上下文读取和 placeholder 渲染，用户会感觉发布动作把主界面短暂锁住。

修改

• 提交后先让 Flutter 完成一帧，把输入面板关闭和 AI 状态按钮画出来，再进入本地提交链路。
• 移除时间线 isSubmitting 的全屏遮罩，保留页面可滚动、可查看。
• 扩展 AgentActivityWidget：任务入队前可强制显示；任务入队后显示后台任务数量；即使还没有首条 Agent/tool activity，也可以点击打开详情。
• 为 LocalTaskExecutor 增加 TaskActivitySnapshot stream，复用现有 bool stream 兼容旧调用方。
• 增加 widget test 覆盖“任务还没产生 activity 时也能看到/打开 AI 处理中状态”。

验证

• flutter pub get --offline
• flutter test --no-pub --concurrency=1 test/ui/agent_activity/agent_activity_widget_test.dart test/data/services/local_task_executor_test.dart
• flutter analyze --no-pub lib/data/services/local_task_executor.dart lib/ui/agent_activity/widgets/agent_activity_widget.dart test/ui/agent_activity/agent_activity_widget_test.dart
• flutter analyze --no-pub 已运行；当前仓库仍有 327 个既有 info 级 lint，命令按现有配置返回 1，本 PR 未在改动文件中引入新的 analyze 问题。

[github-actions]

PR Preflight Summary / PR 预检汇总

中文

• 统一结论：低风险：两个预检均已完成，质量预检通过，可走普通手动合并流程。
• Policy preflight：低风险。未命中打回、高风险或警告规则。
• Flutter quality：通过。Analyzer 和 test baseline 均未发现新增问题。
• PR head：308ffa500215aeda151a36944b066e504724d1fa
• Policy run：26040248627
• Flutter run：26040248512

English

• Combined result: Low risk: both preflights completed and quality passed; use the normal manual merge flow.
• Policy preflight: LOW RISK. No blocking, high-risk, or warning policy signal was found.
• Flutter quality: PASS. Analyzer and test baselines found no newly introduced issue.
• PR head: 308ffa500215aeda151a36944b066e504724d1fa
• Policy run: 26040248627
• Flutter run: 26040248512

PR Policy Preflight / PR 规则预检

PR Policy Preflight / PR 规则预检

中文

• 判定：低风险
• 变更文件数：0
• 变更行数：0
• Diff 是否截断：false

未发现确定性规则问题。

English

• Decision: LOW RISK
• Changed files: 0
• Changed lines: 0
• Diff truncated: false

No deterministic policy findings.

PR Flutter Quality / Flutter 质量预检

PR Flutter Quality / Flutter 质量预检

中文

• 总体：通过
• Analyzer baseline：通过
• Test baseline：通过

English

• Overall: PASS
• Analyzer baseline: PASS
• Test baseline: PASS

Flutter Analyzer Baseline

• Base issues: 331
• PR issues: 327
• New issues: 0

No new analyzer issues introduced by this PR.

Flutter Test Baseline

• Base failures: 0
• PR failures: 0
• New failures: 0

No new Flutter test failures introduced by this PR.