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npub1cc3ha7z055mu0rwwu7806t2wt8mj3pvu0uv5mfp2c50dahaqhczshdalg6andtlongwell-block 4354fe3bc2 fix(terminal): repaint the whole viewport when the active session changes

Switching tabs left the outgoing session's text on screen. Only the cursor
line moved, because `apply()` re-dirties it.

`TerminalGrid` drains its dirty set in `paint()`, not in `apply()` (the sole
`#dirty.clear()` is the last statement of `paint`). So an inactive session
accumulates dirty lines and repaints fine on the first switch to it -- the
failure needs a round trip. Once a grid has been painted and then deactivated,
it holds rows with an empty dirty set, and the paint effect swapped `gridRef`
without marking anything: `paint()` drew zero lines and the canvas kept the
previous session's pixels.

`markAllDirty()` alone is not sufficient. Switching to a session that has
delivered no frame yet has no grid at all, so `markAllDirty()` and `paint()`
are both no-ops on the optional chain, and only the background fill can erase
the outgoing session. The fill is therefore not grid-guarded, and it covers the
full canvas bounds rather than `columns * cellWidth`, which leaves a gutter.

Both refs are read-then-written after the effect's early returns, so a pass
that bails on a missing canvas or context keeps the switch pending instead of
swallowing it.

Four tests, each pinned by a mutant that only it kills: the round trip, the
no-frame case, a negative test that a frame on an unchanged session does not
force a full repaint (guarding the damage model against a permanently-true
`sessionChanged`), and the bailed-pass case. The suite's `getContext` stub
discarded every argument, which makes any assertion about painting vacuous;
it now records draw calls keyed by canvas element so the banner canvas cannot
be mistaken for the grid.

Co-authored-by: tlongwell-block <109685178+tlongwell-block@users.noreply.github.com>
Signed-off-by: tlongwell-block <109685178+tlongwell-block@users.noreply.github.com>

2026-08-02 21:50:00 -04:00