feat: Store an expiry per presence row - #541

Closes #539.

Each row now carries its own expiry, so a writer that knows when its clients leave can write once and remove the row itself, instead of re-stamping it inside the TTL.

Before

sequenceDiagram
    participant W as Writer
    participant DB as wp_presence
    participant R as Reader
    W->>DB: set_presence() stamps date_gmt
    loop every ~120s, or the row vanishes
        W->>DB: re-stamp date_gmt
    end
    R->>DB: live if date_gmt > now - TTL

After

sequenceDiagram
    participant W as Writer
    participant DB as wp_presence
    participant R as Reader
    W->>DB: set_presence( ..., expires_in ) once
    R->>DB: live if expires_gmt > now
    W->>DB: remove_presence() when the client leaves
    Note over DB: cron deletes expires_gmt <= now

Shape

• expires_gmt is always set, so every liveness check is one indexed predicate.
• The expiry is computed from the clamped $date_gmt, so a backdated row expires on the writer's clock.
• wp_presence_max_expires_in caps the window, default one hour. The privacy policy text and the personal data export report that cap, since it is the most any row can outlive its last activity.
• wp_presence_default_ttl applies at write time. Changing it does not re-age stored rows; anyone still present picks up the new value on their next ping.
• The redundant-write guard no longer skips a row whose expiry falls inside the next tick gap, since a skipped write would leave it to run out.

Most likely to be wrong

• $timeout on the readers is a no-op. Honouring it means expires_gmt > %s AND date_gmt > %s, the predicate this removes. The parameters stay because dropping a positional argument turns wp_get_presence( $room, 30 ) into a prefix lookup that silently returns nothing. _deprecated_argument() on a non-default value is the natural next step; A site's wp_presence_default_ttl filter overrides a consumer's own timeout window #515 is the case for keeping the narrowing.
• No migration step. Pre-existing rows carry the zero default, read as expired, and the scheduled cleanup collects them within the minute; wp presence cleanup does it at once.
• Cleanup boundary is now expires_gmt <= %s; it read date_gmt < %s while reads used >, leaving a row on the cutoff neither live nor deletable.

Tested

Single-site (518 tests, 143 skipped) and multisite (518, 3 skipped)

Use of AI Tools

Claude Code (Fable 5)