fix(summarize): 缺 setDistillCursor 时降级内存游标而非抛错

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背景

#274 复审（Anans-Ivresse APPROVED）留了三条非阻塞建议，本 PR 落第 1 条；第 2、3 条经评估不做，理由见下。

变更

persistCursor 在 service.setDistillCursor 缺失时不再抛错，降级为 warn + 内存游标（lastDistilledSeq Map，#274 之前的语义）：

• 动机：第三方宿主用旧版 service 构造插件时，fix(summarize): 持久化增量蒸馏游标（#229） #274 之前靠内存游标正常工作；fix(summarize): 持久化增量蒸馏游标（#229） #274 之后每次蒸馏提交都会在缺方法分支崩掉。降级把这条回归修掉。
• 降级语义：本进程内游标照常推进（不重复蒸馏），跨重启的窗口重放由 saveWithDedupe 三元组 + summarizeDedupeMinSim 向量近重档兜底（[Bug] lastDistilledSeq 为进程内存态：宿主重启后蒸馏窗口从头重放，已蒸馏历史被重复处理 #229 边界确认时已接受的成本）。
• 语义边界不动：方法存在但抛错仍向上传播、触发事务回滚——那是「写失败须回滚」的恰一次语义，对应 summarize.test.js 既有回滚用例保持原样。

测试

• 新增回归用例：删掉 service.setDistillCursor 后蒸馏照跑、记忆落库、无持久化游标、第二轮不重蒸（内存游标生效）。
• npm test：1248 tests，1247 passed + 1 skipped，0 fail（含新用例）。
• npm run sync + check-sync 通过（src ↔ lib 平价）。

不做的两条（Anans 建议第 2、3 条）

• 第 2 条「读路径内存优先」不改：memoryDir 允许双宿主共用（store 的 WAL + busy_timeout 多进程就绪，AGENTS.md 并行协作节）。读库优先是跨进程游标一致的依据——两个宿主进程各持内存 map 互相看不见对方推进的游标，恰好复活 [Bug] lastDistilledSeq 为进程内存态：宿主重启后蒸馏窗口从头重放，已蒸馏历史被重复处理 #229 要修的重复蒸馏，只是从「跨重启」变成「跨进程」。SQLite 主键点查微秒级，turn/end 是人类频率，收益不抵风险。
• 第 3 条「峰值时段/最小窗口 × 持久化游标交叉用例」不补：restart 恢复与 bypassPeak 各有既有覆盖，两条路在 previousSeq 计算处汇合，交叉场景结构上已走通；补测属于为覆盖数字写测试。

Fixes #274（复审建议跟进）

Summary by CodeRabbit

• Bug Fixes
  • 兼容未提供持久化游标功能的旧版服务：摘要处理不再因此中止，改为使用进程内游标继续运行。
  • 增加警告日志，帮助识别未启用持久化游标的运行环境。
  • 同一进程内重复处理相同事件时，仍可避免重复摘要。

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📝 Walkthrough

Walkthrough

当 service 缺少 setDistillCursor 时，persistCursor 现在记录警告并返回。流程改用内存游标。方法存在但抛错时，错误仍向上传播。新增回归测试覆盖该兼容行为。

Changes

游标兼容性

Layer / File(s)	Summary
内存游标降级与回归验证 dsh-mneme/src/summarize.js, dsh-mneme/lib/summarize.js, dsh-mneme/test/summarize.test.js	当 setDistillCursor 不是函数时，代码记录警告并跳过持久化。首次处理仍执行 LLM 蒸馏并保存记忆。同一进程再次处理相同窗口时，内存游标阻止重复蒸馏。现有的持久化写入错误仍继续传播。

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Suggested reviewers: z2ace0107

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 3 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	标题准确概括了主要变更：当缺少 setDistillCursor 时，改为使用内存游标而不是抛出错误。标题简洁且与代码变更和 PR 目标一致。
Linked Issues check	✅ Passed	[#274] 的持久化游标、事务回滚和失败传播实现已在评审头中保留。本次 diff 同步修改 src/summarize.js 与 lib/summarize.js：当旧版 service 缺少 setDistillCursor 时记录 warning 并使用进程内游标；当方法存在但抛错时仍传播错误。新增测试验证蒸馏、记忆写入、无游标持久化和进程内去重。该兼容分支不改变 [#274…
Out of Scope Changes check	✅ Passed	本次变更仅涉及 [#274] 的游标兼容逻辑、src/ 与 lib/ 的同步，以及对应回归测试。warning、旧版宿主降级和进程内去重都直接服务于游标兼容目标。未发现与 [#274] 无关的代码或测试变更。

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