Caddy's `file_server` did not set Cache-Control on the SvelteKit
build, so browsers fell back to heuristic caching keyed off
Last-Modified. On the long-lived dev environment the heuristic
window leaves the previous deploy's `index.html` cached for
minutes-to-hours, and Safari combined that with stale conditional
requests into a visible multi-second freeze on every reload (the
reproduction was "private window reloads instantly, normal window
hangs; clearing Safari caches restores normal speed"). Push
delivery itself works — heartbeat keeps the SubscribeEvents stream
alive — but the bundle path stalls behind the browser revalidating
a chain of stale chunks.
Mirror the standard SvelteKit cache split inside both Caddyfiles:
- `_app/immutable/*` — hash-named JS/CSS chunks Vite emits with
content-addressed file names — `Cache-Control:
public, max-age=31536000, immutable`. Safe to cache forever
because the name changes whenever the content does, so the next
deploy serves new files under new URLs.
- Everything else (`index.html` fallback via `try_files`,
`env.js`, `version.json`, `core.wasm`, `wasm_exec.js`,
`favicon.svg`) — `Cache-Control: no-cache, must-revalidate`.
The browser still uses the cached body when the ETag matches,
but it always asks first; a fresh deploy reaches the user on
the next reload without a manual cache clear.
Smoke-tested locally: a docker-run Caddy with this config returns
the immutable header only for `/_app/immutable/*` and the
no-cache header for `/index.html`, `/env.js`, and the SPA-fallback
path `/some/route`. The Caddyfile passes `caddy validate` in
both `Caddyfile.dev` and `Caddyfile.prod`; the pre-existing
formatting warning on line 7 is untouched.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Ilia Denisov