fix: restore manual context compaction for direct models

Local direct-model text conversations could not use manual context compaction,
and disabling automatic compression prevented saved summaries from being reused.
Restore the composer action regardless of the automatic setting or threshold,
use the selected summary connection, and persist summaries for subsequent
requests while retaining recent turns and full conversation history.

Image connections, remote channel conversations, and SSH projects remain outside
the local direct-model compaction workflow. Add focused regressions, a local
Electron end-to-end test, and an opt-in two-request live probe.

Validation: staged snapshot passed typecheck, changed-file ESLint, 13 focused
tests, and the Electron end-to-end test with two local HTTP fixture requests.
No additional real-model calls were made during commit verification.

Release note: 修复本地直连文本模型无法手动压缩上下文的问题。现在关闭自动压缩或尚未达到触发阈值时，也可点击“压缩上下文”；摘要会随会话保存并用于后续对话，同时保留最近轮次和完整历史。

docs/features/direct-model-agent/technical-design.md

@@ -451,6 +451,18 @@ type SubagentActor =
 处理。Continue 接收完整历史，已有有效摘要只替换其覆盖的前缀，剩余消息全部交给原生
 Runtime；GoodBuddy 不再额外保留最后 20 条或限制为 128,000 字符。
 
+### 10.1 本地直连手动压缩
+
+`agentCompactConversation` 接受 `model`，结果保留实际 provider，压缩策略为
+`goodbuddy-summary`。摘要来源为 `current` 时，IPC 使用 `applyRuntimeSelection`
+解析后的当前直连连接；来源为 `profile` 时，使用既有指定摘要连接配置。
+图像连接不进入文本摘要路径，SSH 执行空间仍由本地 IPC 拒绝。
+
+`ModelAgentRuntime.compactConversation` 复用 `prepareCompressedRequest` 的强制压缩，
+跳过自动开关和触发阈值，保留最新轮次。返回的 `contextCompressionState` 沿用会话保存，
+不删除历史正文。后续请求校验摘要覆盖范围后，用摘要替换已覆盖前缀；即使关闭自动压缩，
+已保存的有效摘要仍会使用。
+
 ## 11. 性能
 
 - Shell 探测按执行服务实例缓存，不在每轮模型调用重复探测。