Say which clock is wrong, and link to how to fix it (GRYT-282)

[sivert-io]

This server's identity proof had expired. Check the clock on both machines.

That asked somebody to inspect a machine they may not own, and made them work out which of the two was wrong. The client already knew — it had just compared the server's timestamp against its own to decide the proof had expired at all.

Now:

This server's clock is about 4 minutes behind yours, so its identity proof looked expired. If it is your server, turn on time sync.

Decisions worth checking

Measured from iat, not exp. That's the one instant both sides describe: the server says when it signed, we know when we read it. The gap is the skew plus a network round trip, and a round trip is milliseconds against a 60-second window, so what survives is the skew.

Rounded to something sayable — seconds, minutes, hours, days. Whether a clock is a minute out or a day out is the useful distinction: the first is a missing time sync, the second is usually a machine that came up with no working clock. A stray hundred milliseconds isn't worth rendering.

The help URL rides beside the sentence, not inside it. The refusal card gets a "How to fix this" link; the toast stays plain text, since a link in something that disappears after 12 seconds is no use. That meant threading refusalHelpUrl through useSockets → useServerState → serverView → ServerLoadingStates, alongside the reason that already goes that way.

Falls back cleanly when a proof carries no iat — a shorter sentence, and without the instruction to go and check two clocks.

Found the hard way

A fresh Debian VPS: System clock synchronized: no, NTP service: n/a, and timedatectl set-ntp true answering NTP not supported because systemd-timesyncd wasn't installed. RTC 65 seconds off the system clock, right past the 60-second window. Completely ordinary situation, and the old message pointed at it correctly while sounding like a client bug.

Verified

Ran serverProofErrorMessage against the real module for 65s each way, 4 minutes, 3 hours, 5 days, 1 second, and a missing iat. Wording and pluralisation correct in each. serverProofHelpUrl returns the link for expired and null for every other refusal, so unrelated failures don't sprout a misleading "how to fix" button.

yarn lint and yarn build clean.

Depends on Gryt-chat/docs#27 for the anchor — merge that first or the link 404s.

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