A tcsh login shell worked on 1.48.0 only because the local sh rewrote
${SHELL:-/bin/sh} to this host's shell. With the launch verbatim, tcsh gets -i -l,
refuses it and every stock launch leaves a dead pane. The changeset and
docs/remote-sessions.md described that as a standing limitation; they now name it
as a change in this release, with what the override workaround costs.
Also: extraSshOptions joins the list of values now literal at launch, the stock pane
command is shown as /bin/sh -c in the docs and the builder's JSDoc, the invariants
state how the launch must reach the far end, the manual pages cover $ in an override,
and the invariants no longer say extraSshOptions refuses a bare $ (it never did).
Reworded the em-dashes on the invariants line this rewrites.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>