changelog: document 2026-05-19 performance improvements

CHANGELOG.md

@@ -1,5 +1,55 @@
 # Changelog
 
+## [unreleased] — 2026-05-19
+
+### Performance — activity detail page
+
+Four targeted fixes that together eliminate the blank loading screen and
+reduce timeseries payload size for the dominant use case.
+
+**sessionStorage summary passthrough** (`ActivityFeed.svelte`,
+`ActivityDetailLoader.svelte`): when the user clicks an activity from the
+feed, the summary object is written to sessionStorage before navigation and
+read back synchronously at module init on the detail page — before the first
+render. The "Loading activity…" screen and the two sequential index-fetch
+round trips are eliminated entirely for this path. Direct URLs and bookmarks
+fall through to the existing slow path unchanged.
+
+**Spatial 10 m downsampling** (`bincio/extract/timeseries.py`): timeseries
+are now downsampled to one sample per 10 m of distance traveled (GPS
+haversine primary, speed × Δt fallback) instead of one per second. Indoor
+activities with neither GPS nor speed data are left at 1 s resolution.
+Running activities see ~67 % fewer points; long cycling rides ~30 %. A
+`bincio render --downsample-timeseries` migration flag retroactively
+downsamples all existing stored files without re-extracting from FIT/GPX.
+
+**nginx timeseries caching** (`deploy/vps/nginx-activity.conf`): a regex
+location block before the generic `/data/` handler serves `*.timeseries.json`
+with `Cache-Control: public, max-age=3600, stale-while-revalidate=3600`.
+Previously every page view triggered a conditional GET even when nothing had
+changed.
+
+**asyncio.to_thread for segment_efforts** (`bincio/serve/routers/activities.py`):
+the synchronous file scan in `GET /api/activities/{id}/segment_efforts` is
+now dispatched via `asyncio.to_thread` so it runs in a thread pool instead of
+blocking the event loop during concurrent fetches.
+
+### Performance — static asset caching
+
+**Immutable JS/CSS caching** (`deploy/vps/nginx-activity.conf`): Astro
+content-hashes all `/_astro/*.js` and `/_astro/*.css` filenames at build time.
+A new nginx location block serves them with `max-age=31536000, immutable` so
+browsers never revalidate until the hash changes. HTML pages get an explicit
+`no-cache, must-revalidate` header so the latest asset URLs are always fetched
+after a deploy.
+
+### Tooling
+
+**VPS backup script** (`deploy/vps/backup-vps.sh`): extended to pull
+`nginx-wiki.conf` and `nginx-planner.conf` in addition to the existing files.
+
+---
+
 ## [0.1.0] — 2026-04-22
 
 ### Improvement — DEM & hysteresis algorithm refinements