The assets are baked into the binary, so their FS modification times are the
zero value and http.FileServer sent no Last-Modified. With no ETag either, a
static response carried no validator at all and the browser was free to guess
how long to keep it -- which is how the panel kept showing the previous favicon
in the tab well after the new mark was deployed.
Hash each asset once at startup and serve that as a strong ETag, with
Cache-Control: no-cache so the browser keeps its copy but revalidates. An
unchanged asset then costs a bodyless 304 and a changed one is picked up on the
next load.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
