fix(desktop): cache external-session catalog per selection so switching sources shows loaded rows instantly

[liuxiaocs7]

Summary

Switching the import source — or toggling the archived filter / editing the search, and including returning to a source already loaded — blanked the list and flashed the full-width "Reading external conversations…" spinner on every switch, because loadCatalog unconditionally reset the catalog and loading flag with no per-selection cache.

This caches the last loaded CatalogState per (adapterId, includeArchived, search): a cache hit renders the rows immediately and refreshes in the background, while a miss keeps the existing spinner. The background import poll now observes the request generation instead of claiming a new one, so it can never strand an in-flight load's catalogLoading reset.

Two follow-ups from review: a cache hit now also clears any stale catalogLoading / loadingMore left by a superseded search or pagination request (so the spinner or a disabled Load More can't strand over otherwise-complete cached rows), and it refreshes through readCatalogWindow seeded with the cached page count, so a multi-page selection keeps every loaded page instead of snapping back to page one when the refresh lands.

Fixes #3904

Verification

• tsc for tsconfig.preload.json, tsconfig.main.json, tsconfig.renderer.json — all clean.
• biome check on both changed files — clean.
• node --test dist/main/__tests__/import-tasks-settings-page.test.js — 22/22 pass (15 existing + 7 source-switching cases).
• Fails without the change: reverting each fix in isolation turns its guarding tests red — the per-selection cache (shows a previously-loaded source instantly with no spinner, does not let a stale background refresh overwrite a newer source selection), the stale-loading reset (clears the reading spinner when a pending search returns to a cached term, clears a pending Load More lock when switching back to a cached source), and the full-window refresh (keeps every loaded page when a revisited multi-page source refreshes); restoring each returns the suite to green (22/22).
• Not run: repo-wide format:check / knip, full npm run build, and the cross-workspace suite. tsconfig.storybook.json reports one pre-existing, unrelated error (UsageRequestLog.sessionName in stories/settings/settings-pages.stories.tsx) that exists on the base commit and this PR does not touch.

Review focus (UI evidence)

I could not capture a headless screenshot of the Electron window in my environment, so the before/after is shown via the deterministic test output above instead of an image. To see it live: run the desktop app, open Settings → Activity → Import Tasks with ≥2 sources, and switch back and forth — a revisited source now appears instantly with no spinner flash (first-time loads still show the spinner).

AI use

Select exactly one:

• No generative tool made a substantive contribution
• Generative tooling made a substantive contribution

Tool(s) and scope: Claude Code (Claude Opus) — root-cause investigation, the per-selection cache implementation, the two review-driven follow-ups (stale-loading reset and full-window refresh), and the added tests. Reviewed and submitted by the human contributor of record; commit carries a Generated-by: Claude Code trailer.

Checklist

• Tests cover the change and fail without it
• Lint, format, typecheck and the affected suites pass locally

Does this PR entail a change in behavior?

• Yes — described under Summary above
• No

[Astro-Han]

Thanks for addressing the repeated blank-loading state when switching external-session sources. Keeping the Host as the catalog authority while caching only the renderer projection is the right boundary, and the selection key plus request generation model is appropriately scoped.

I left one inline P2 for a recoverable stale-loading case. It does not risk catalog correctness or persisted data, so I am approving the overall direction, but clearing the obsolete loading state would make the cache behavior complete.

Reviewed with Codex and an independent @Reviewer agent. I verified the exact head, cache ownership, selection and request generations, switching and import-recovery paths, and passing CI.

中文对照

谢谢你处理切换外部 Session 来源时反复出现空白加载状态的问题。Host 仍然是 catalog authority，renderer 只缓存展示 projection，这个边界是正确的；selection key 和 request generation 的范围也比较合适。

我留了一条 P2 行内评论：切回缓存 selection 时，旧的 loading 状态可能没有被清理。它不会影响 catalog 正确性或持久化数据，因此我认可整体方向；不过清理过期 loading 状态可以让缓存行为真正闭环。

本次审查使用了 Codex 和一个独立的 @Reviewer 子代理；我核对了精确 head、缓存职责、selection 与 request generation、切换和导入恢复路径，以及 CI 结果。