SecurityHeadersMiddleware called set_security_headers() on every
response — 14 os.environ.get lookups plus a regex validation per
configured header, for values that are static for the process
lifetime. Compute the header list once at construction; when no
security env vars are set, skip wrapping send entirely.
RedirectMiddleware decoded and parse_qs'd the query string of every
GET, though it only acts on /watch?v= and ?shared= URLs. Add a cheap
path/substring precheck first; a false positive just falls through to
the previous full parse, so no redirect behavior changes.
Verified byte-identical responses (status, Location, header values)
against the previous implementations across redirect, passthrough,
and no-env cases.
Claude-Session: https://claude.ai/code/session_01MHg5zs1VBjvRWQ54qHpfYD
Co-authored-by: Claude <noreply@anthropic.com>
