fix(tui): single layout authority for viewport rows#124
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Streaming cards and approval modals each read stdout.rows and
computed their own row budget independently — the bottom-anchor
modal could claim rows the streaming card had already counted on
and vice versa, producing visible jitter when both rendered the
same frame (lamyc's video).
Replaces the scattered RESERVED_CHROME_ROWS / MODAL_OVERHEAD_ROWS
constants with a priority-greedy allocator. Each component declares
{ min, max } rows for its zone via useReserveRows; the provider
runs allocation and feeds back actual budgets so consumers stay
within the viewport.
Migrated zones, in priority order:
modal (EditConfirm, ShellConfirm, PlanConfirm,
PlanCheckpointConfirm, ChoiceConfirm)
status — left for follow-up; already conditionally hidden
input (PromptInput multi-line)
stream (StreamingCard)
safety — reserved margin
Skipped this pass: PlanCard anchor, plan-card zone, status rows.
Those don't trigger the lamyc bug and can plug into the same API
when their behavior is reviewed.
The hook had `ctx` in its effect deps, but the provider's context value identity changes after every dispatch (the memo depends on `allocations` which recomputes whenever `claims` changes). So claim → state update → new ctx identity → effect re-fires (release + claim) → infinite loop. Depend on `dispatch` (stable from useReducer) and the spec primitives instead. Effect now fires once on mount, again only when min/max actually change, and once on unmount.
This was referenced May 2, 2026
ChasLui
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May 23, 2026
* fix(tui): single layout authority for viewport rows (esengine#120) Streaming cards and approval modals each read stdout.rows and computed their own row budget independently — the bottom-anchor modal could claim rows the streaming card had already counted on and vice versa, producing visible jitter when both rendered the same frame (lamyc's video). Replaces the scattered RESERVED_CHROME_ROWS / MODAL_OVERHEAD_ROWS constants with a priority-greedy allocator. Each component declares { min, max } rows for its zone via useReserveRows; the provider runs allocation and feeds back actual budgets so consumers stay within the viewport. Migrated zones, in priority order: modal (EditConfirm, ShellConfirm, PlanConfirm, PlanCheckpointConfirm, ChoiceConfirm) status — left for follow-up; already conditionally hidden input (PromptInput multi-line) stream (StreamingCard) safety — reserved margin Skipped this pass: PlanCard anchor, plan-card zone, status rows. Those don't trigger the lamyc bug and can plug into the same API when their behavior is reviewed. * fix(viewport-budget): break infinite useEffect loop in useReserveRows The hook had `ctx` in its effect deps, but the provider's context value identity changes after every dispatch (the memo depends on `allocations` which recomputes whenever `claims` changes). So claim → state update → new ctx identity → effect re-fires (release + claim) → infinite loop. Depend on `dispatch` (stable from useReducer) and the spec primitives instead. Effect now fires once on mount, again only when min/max actually change, and once on unmount.
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Closes #120.
Why
StreamingCard,EditConfirm,ShellConfirm, and friends each readstdout.rowsand computed their own row budget independently. Two scattered constants encoded the assumption:RESERVED_CHROME_ROWS = 14(StreamingCard) andMODAL_OVERHEAD_ROWS = 18(EditConfirm). Neither knew about the other.Result: when an approval modal mounted while a tool card was still streaming (lamyc's video — write_file streaming + plan checkpoint approval), both layers claimed rows that together exceeded the viewport. Ink reflowed every frame, producing visible vertical jitter.
The class-of-bug part: every new bottom-anchored component added another independent calculation. A targeted patch would land another magic constant; the next bug just moves to a new component.
What
src/cli/ui/layout/viewport-budget.tsx—ViewportBudgetProvider+useReserveRows(zone, { min, max })hook + pureallocateRows()allocator. Priority-greedy:modal > plan-card > status > input > stream > safety.StreamingCard,EditConfirm,ShellConfirm,PlanCheckpointConfirm,PlanConfirm,ChoiceConfirm,PromptInput. Each declares its zone claim; the provider runs allocation and feeds back actual budgets.RESERVED_CHROME_ROWSand the standaloneMODAL_OVERHEAD_ROWSreads are gone.useTotalRows()/useIsModalActive()replace directuseStdoutreads in those paths.Out of scope (follow-up)
PlanCardanchored render in App.tsx — small height, doesn't trigger this bug, can plug in next pass.OngoingToolRow,ThinkingRow, etc.) — already conditionally hidden during modals, don't compete.SessionPicker,McpBrowser,PlanReviseEditor) — independently take the viewport, not a competing layer.Verification
npm run verify— typecheck, lint, build, 1791 tests all greentests/viewport-budget.test.ts) covering single/multi claim, priority order, undersize-terminal fallback, and the lamyc scenario specifically