Second half of the "large message history slows the interface down" report. The
first half (4058f8d) removed the repeated ring scan; this bounds how much history
a single chat can accumulate in the first place, which is what was asked for in
the channel: a configurable limit, with a lower default, and a warning.
Until now the message store was one shared ring with no per-chat bound, so a busy
public channel could occupy essentially all of it. That both starved every other
chat of its history and kept the ring permanently full, which is the condition the
slow paths were suffering under. The reporter had 3800 messages in one channel.
- New pref hist_per_chat (touch-cfg v42), default 250 messages per chat. Chosen
to be deep enough to scroll back through a conversation while staying far below
the 5000-record SD ring, so no single chat can dominate it.
- Enforced on append: enforceHistoryCap() blanks that chat's oldest records until
it is back within the limit. It walks from the oldest end, so for the chat that
is actually over the cap (the one filling the ring) the records it wants are
found immediately rather than after a full scan.
- Settings -> Chats: "Keep per chat (messages)" — 100 / 250 / 500 / 1000 / 2000 /
No limit, with a line explaining that older messages are dropped past the limit.
- "No limit" is a deliberate choice, not a silent one: it raises a confirmation
saying a busy channel can then fill the whole store and make things slower. The
dropdown reverts first and only commits from the confirm handler, so dismissing
the dialog leaves the previous limit in place.
The thread-history cache from 4058f8d becomes a per-thread COUNT rather than a
bool, since the cap needs to know how many records a chat holds; "has history" is
just count > 0, so the O(1) inbox behaviour is unchanged.
Existing installs pick up the 250 default and will trim on the next message in an
over-long chat. Anyone who wants the old unbounded behaviour can select No limit.
Builds clean on V4 + T-Deck; flashed to the T-Deck.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
