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Will PflegerandGitHub 294c8c821d perf(desktop): move observer-feed archive and decrypt commands off main thread (#3415 )

Opening the agent observer feed could beachball the app. In Tauri 2, a
sync (`pub fn`) command body runs on the **main thread** — only `async
fn` commands run on the runtime pool. Five commands on the observer-feed
open path were sync, so panel open ran SQLite I/O and secp256k1 work on
the macOS main thread:

| Command | Main-thread work |
|---|---|
| `decrypt_observer_event` | Schnorr ID + signature verify, then NIP-44
decrypt — once per frame |
| `read_archived_observer_events_for_channel` | Opens the archive DB,
runs the channel-index JOIN, returns up to 200 raw JSON blobs per page |
| `read_unindexed_observer_rows` | Opens the DB, returns **all**
not-yet-indexed kind-24200 rows in one shot |
| `index_observer_channel_id` | Opens the DB, loops N upserts |
| `delete_save_subscription` | Opens the DB, one delete |

Eager hydration loads up to 10 pages × 200 frames on panel open, so
that's up to 10 main-thread DB reads plus up to 2,000 sequential
verify+decrypt calls before any scrolling. The one-shot backfill makes
it worse on the first open after history accumulates: one read of every
unindexed row, a decrypt per row, then a batch upsert — all on the main
thread, and all proportional to archive size.

The four archive commands now route their DB work through the existing
`run_archive_db_task` helper (`spawn_blocking` + `open_db`), matching
`list_save_subscriptions`, `read_archived_events`, and `archive_events`
directly around them. `decrypt_observer_event` becomes `async fn` +
`tauri::async_runtime::spawn_blocking`, with `state.signing_keys()`
extracted before the spawn since `State` is not `Send` — the same
pattern `sign_event` uses from #1222.

No frontend changes: `invoke` is already promise-based, so the TS
wrappers in `tauriArchive.ts` and `tauriObserver.ts` are unchanged.

This removes the freeze, not the work. Eager hydration still takes the
same wall time — the feed shows a loading state instead of blocking the
UI. Batching the per-frame decrypt IPC (2,000 round-trips into one
command) would cut the latency itself; that's deliberately out of scope
here.

Signed-off-by: Will Pfleger <pfleger.will@gmail.com>

2026-07-29 11:17:35 -04:00