pastilhas fe7fe49cee chat: stop reassigning a live session to fable ...

three defects, one shape: the code has two names for "which session is this",
and every guard checked the one no caller uses.

`fable` is the FIRST entry in the claude-code catalogue, so it is what
ModelSelector picks whenever it decides a conversation needs a default. On a
key without fable entitlement that lands as a 429, after a real mid-session
switch — the reported header read OPUSPLAN → FABLE.

1. the settings default was applied to RESUMED chats. the guard was
   `!initialSessionId`, and no chat caller passes that when resuming — the id
   arrives as `options.resumeSessionId`, and ChatPanelWrapper goes as far as
   `resume ? undefined : sessionKey`. so a user's default model was written
   over sessions that already had one. both names are checked now.

2. `hasStarted` was `!!preloadedMessages?.length`, which is FALSE for the
   first frames of a resumed chat — before its messages arrive. ModelSelector
   reads "not started" as permission to pick a default, so a reload reassigned
   live sessions during that window. a session id is known on the first render
   and a chat that has one is by definition not new.

3. harness lock. `crossesHarness` returned false when the current harness was
   unknown, which reads as "nothing crosses" and is the opposite of what is
   known — with no current harness, everything might. so a started session
   offered a switch to opencode while its model was still resolving, a switch
   that cannot work: it hands a `ses_…` id to `claude --resume` and dispatches
   to the wrong sidecar. unknown is not permission; the strip locks until the
   answer arrives.

the settings themselves were never wrong — chat.defaultModel reads
claude-code/opus on the affected server. nothing was ever reading it for the
sessions that got reassigned.

2026-08-20 00:32:44 +00:00

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