Bottom-panel Stage 2B-3, part 2 of 3: the pixel substrate for the band.
`text_area_bottom` was three boundaries wearing one name — its own doc
comment called it "the single source for every bottom-of-text
computation" — and once a band can be installed they must diverge:
status_band_top = max(0, height - status_band_height)
geometry_capacity_bottom = max(0, status_band_top - divider_height)
document_text_bottom = max(0, status_band_top - installed_band)
The census is 29 matches: 20 production call sites, 1 definition, 8 test
sites. All 20 were read in their enclosing function and classified
individually — 8 status-owned, 12 document-owned. A blanket rewrite that
subtracted the band from all of them would move the status chrome with
the document and pass an "everything moved" assertion, which is why the
classification is per site and the criterion asserts both directions.
The three easiest to get wrong keep their named symptoms: document
completion placement is document-owned (status-owned would overlap the
band), minibuffer candidate clipping is status-owned (the minibuffer is
global bufferless chrome anchored to the band, and clipping it at the
document boundary would cut it off), and edge scrolling is document-owned
(left on the old bottom it would auto-scroll from inside the panel).
`geometry_capacity_bottom` reserves the divider even while the panel is
absent. That asymmetry is what breaks the first-open cycle: the daemon
sizes a panel from the capacity it was told about, so a capacity that
ignored the divider would grant a first panel that does not fit once the
divider appears beside it. The document loses no pixels until a `Present`
frame is really on screen.
`PanelBandInset` is a newtype, not an `f32`, because three boundaries here
take a pixel height and only one takes this one.
Alongside it, the band's own machinery: `PanelBand` with ONE derivation of
"is a panel on screen" (`presented()` — retained valid frame, matching
geometry epoch, latch clear), the frontend-owned epoch state machine with
its fail-closed exhaustion latch, the `Absent`-is-authoritative receipt
path, `panel_cell_capacity` (no per-axis cap — a panel may legitimately be
wider than a PTY — plus the daemon's virtual status row), the stable
normal-face probe for column count, and the divider strip whose paint rect
IS its hit rect.
`TerminalPaintPlan::build_grid` factors the shared cell planner so a panel
and a terminal cannot disagree about a wide-continuation pair; terminal
selection spans stay outside it rather than being faked as empty inside.
`PANEL_MIN_VERSION` moves into `pmacs-protocol` so the GPU frontend aliases
one definition instead of restating 21.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Lv428Fth9LRtffwJSsqH7T
Levi Neuwirth
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