[Bug] @ mention menu takes 3-4s per keystroke: session-reference titles re-decompress every persisted session log (archived/subagent sessions included), no cache, no debounce

[Yingjie-Zhao]

Problem

In 0.1.0-rc.8 the composer @ menu (the new file & session references feature) takes 3–4 seconds every time before candidates render — and this repeats on essentially every keystroke, not just the first open. Directory-scoped queries like @personal/ are equally affected, even though the file side alone would be a single readdir.

Environment: @deepseek-ai/dsh@0.1.0-rc.8 from npm, dsh web on macOS 26, ~67 persisted sessions / 40 MB of session.jsonl.zstd logs / ~148k events in ~/.dsh/sessions.

Root cause (from the rc.8 sources)

The slowness is on the session-reference side, not the file side:

1. Client gating + no debounce. dsh-client-ui-reference resolves candidates via await Promise.all([fileReferences.list(...), sessionReferenceResolver.candidates(...)]), so instant file results are blocked by the slow session query. dsh-client-ui-input-trigger fires one RPC pair per keystroke with no debounce.

2. No pre-filtering in dsh-session-reference. In listCandidates, when the query is non-empty, inspected = records — all sessions are passed to readTitleSnapshots before the needle filter and slice(0, limit) are applied.

3. Title snapshots re-read everything. readTitleSnapshots → SessionCorpus.projectMany → inspectPersisted opens, zstd-decompresses and JSON.parses each session's complete log (147k events in my case) just to fold the latest session/title event. The session_projcache.json store only accelerates listSessions headers; there is no title index. Nothing caches the result between keystrokes.

4. Archived and subagent sessions are scanned too. The workspace registry's archivedSessionIds is only consumed by sidebar grouping; sessionQuery.listSessions has no notion of it. On my machine 46 of 67 persisted sessions (30.6 MB) were archived — invisible in the sidebar and unreachable via the UI (rc.8 has archiveSession but no unarchive affordance) — plus 17 leftover origin: 'subagent' session dirs, and every one of them is fully decompressed on every @ keystroke.

(Secondary, file side: a bare fuzzy query triggers a full workspace BFS capped at 10k entries — only .git/node_modules excluded — and the index is invalidated on every tool/result, so it rarely survives an active session. This is fine on small trees but adds up on large ones.)

Measured

• Simulating the host work — decompress + parse all 67 logs with 4-way concurrency: ~3.6 s, matching the observed 3–4 s per keystroke almost exactly.
• After moving the 62 non-visible session dirs out of ~/.dsh/sessions (40 MB → 5.6 MB), the same menu renders in ~0.5 s.

Suggested fixes

1. In listCandidates, filter records by sessionId/cwd (and rank) before calling readTitleSnapshots, and apply the limit first; only resolve titles for the surviving candidates.
2. Persist a lightweight title index (e.g. extend the projection cache with latest-title + log mtime) so listing candidates never opens full logs.
3. Have session-reference candidates respect archivedSessionIds and skip origin: 'subagent' sessions (or rank them last).
4. Client: debounce @ keystrokes, and render file/session sections independently instead of one Promise.all gate.

User-side workarounds

• Use the quoted form @"path" — quoted queries short-circuit the session resolver entirely (quoted === true → Promise.resolve([])), so only the fast file path runs.
• Move old/archived session directories out of ~/.dsh/sessions (keep a backup) and restart dsh web; the scan cost is linear in total session-log bytes.

I searched the repo's discussions and did not find an existing report for this (Issues are not enabled on the repo, so filing here per community convention).

---

（中文简述：rc.8 的 @ 菜单每次按键都要 3–4 秒，根因不在文件扫描，而在会话引用侧——非空查询时不做预过滤就对全部持久化 session 调用 readTitleSnapshots，每次都把每个 session.jsonl.zstd 完整解压+逐行 JSON.parse（实测 40MB/14.7 万行 ≈ 3.6s），且不看归档标记（46 个已归档 + 17 个子代理残留照样全量扫）；客户端无防抖且 Promise.all 让秒出的文件结果陪等。建议：先过滤/截断再读标题、建标题索引、尊重 archivedSessionIds、客户端防抖并分段渲染。临时绕过：用引号形式 @"..." 跳过会话侧，或把旧会话目录移出 ~/.dsh/sessions 后重启。已检索 discussions，未见同类报告。）