# U4 landed — lifetime is derived, not declared

_2026-09-22 · booth_

**A booth's lifetime stopped being a boolean somebody remembered to press.**
Three states now, and `sweep_once` is the only thing that honours the first two:

    KEPT       `.forever` present                        never swept   (unchanged)
    HELD       an open pick, or marks we cannot read     never swept   (new)
    EPHEMERAL  everything else                           24h           (unchanged)

Plus **viewing is activity**: a deliberately-served response from a booth's own
page route writes `.viewed`. That dotfile is not a `.lock` dotfile, so
`_newest_mtime` already counts it — **there is no new arithmetic anywhere**.
`booth_age_seconds`, `is_expired` and `expires_in` are byte-for-byte what they
were. A view is one more thing in the tree, which is the same trick `.booth.json`
used in U5.

**What counts as a view, and why the exclusions matter more than the inclusions.**
`/b/<n>/` (gallery, verbatim report, `?download=1` zip), `/b/<n>/view` and
`/b/<n>/marks` count. `/b/<n>/marks.json`, asset GETs, `/`, `/healthz` and a
zoom URL that 404s do NOT. The marks.json exclusion is load-bearing: **an agent
must not be able to hold its own booth open by polling for the answer it is
waiting on.** `/b/<n>/asks` is a 308 into `/marks` and records through it — one
call, not two.

Checked because it would have been silent: **nothing in the fleet polls a booth
page.** Homepage's `siteMonitor` for the Booth is `/healthz`, which is on the
not-a-view list. Had it been pointed at a booth URL, every booth would have
become immortal on deploy and nothing would have reported it.

**The hold is unbounded and that is the point** — unanswered is unfinished. What
makes it safe is visibility plus two exits that already existed: the card and
every Booth-owned header say `held until answered` where the countdown was, and
`booth rm` / the UI x / `DELETE /b/<n>` take a held booth exactly as they take a
kept one. **A hold is protection from the timer, never from the operator.**

**Release is activity, stated rather than accidental.** Releasing a kept board
still buys a full TTL — unchanged — but now because `booth_unkeep` calls
`record_view`, which is a rule, and no longer because unlinking a file happened
to bump a directory's mtime, which is not. The CLI warning against
"unkeep and let it expire" stays and stays true.

⚠ **Running `scripts/layout-probe.py` over booth pages resets every booth's
clock**, because a GET of a booth page is a view and the probe is not exempt
from its own rule. Harmless, recoverable, and noted in the probe so nobody
debugs it later as a sweeper that stopped working.

Contract: `docs/contracts/u4_derived_lifetime.contract.md`. Both heid panels ran
and the bug hunt after them; see the sibling entries.