Stripping forwarding headers kept our IP and chain out of reach, but the
User-Agent went through untouched. Clients that fell back to their own name
("crawlkit-roles", "crawlkit-virk", ...) tied all ten exits together as one
actor, and one missing UA meant Go-http-client. The proxy now overwrites the
UA on every request (WEIRCON_USER_AGENT, default current Firefox) and the
egress prober uses the same string.
Also dropped: From, Sec-Ch-Ua* (would contradict a Firefox UA) and any
X-Weircon-* by prefix. New end-to-end test drives the whole handler and
checks what the target actually receives.
Claude-Session: https://claude.ai/code/session_01AUj1LSMmrowcomkn1ciAgj
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