fix(tmux): prefer split-or-defer with FIFO deferred attach

src/features/tmux-subagent/pane-split-availability.ts

@@ -1,14 +1,15 @@
-import { MIN_PANE_WIDTH } from "./types"
 import type { SplitDirection, TmuxPaneInfo } from "./types"
 import {
-  DIVIDER_SIZE,
-  MAX_COLS,
-  MAX_ROWS,
-  MIN_SPLIT_HEIGHT,
+	DIVIDER_SIZE,
+	MAX_COLS,
+	MAX_ROWS,
+	MIN_SPLIT_HEIGHT,
 } from "./tmux-grid-constants"
+import { MIN_PANE_WIDTH } from "./types"
 
-function minSplitWidthFor(minPaneWidth: number): number {
-	return 2 * minPaneWidth + DIVIDER_SIZE
+function getMinSplitWidth(minPaneWidth?: number): number {
+	const width = Math.max(1, minPaneWidth ?? MIN_PANE_WIDTH)
+	return 2 * width + DIVIDER_SIZE
 }
 
 export function getColumnCount(paneCount: number): number {
@@ -25,16 +26,16 @@ export function getColumnWidth(agentAreaWidth: number, paneCount: number): numbe
 export function isSplittableAtCount(
 	agentAreaWidth: number,
 	paneCount: number,
-	minPaneWidth: number = MIN_PANE_WIDTH,
+	minPaneWidth?: number,
 ): boolean {
 	const columnWidth = getColumnWidth(agentAreaWidth, paneCount)
-	return columnWidth >= minSplitWidthFor(minPaneWidth)
+	return columnWidth >= getMinSplitWidth(minPaneWidth)
 }
 
 export function findMinimalEvictions(
 	agentAreaWidth: number,
 	currentCount: number,
-	minPaneWidth: number = MIN_PANE_WIDTH,
+	minPaneWidth?: number,
 ): number | null {
 	for (let k = 1; k <= currentCount; k++) {
 		if (isSplittableAtCount(agentAreaWidth, currentCount - k, minPaneWidth)) {
@@ -47,30 +48,26 @@ export function findMinimalEvictions(
 export function canSplitPane(
 	pane: TmuxPaneInfo,
 	direction: SplitDirection,
-	minPaneWidth: number = MIN_PANE_WIDTH,
+	minPaneWidth?: number,
 ): boolean {
 	if (direction === "-h") {
-		return pane.width >= minSplitWidthFor(minPaneWidth)
+		return pane.width >= getMinSplitWidth(minPaneWidth)
 	}
 	return pane.height >= MIN_SPLIT_HEIGHT
 }
 
-export function canSplitPaneAnyDirection(pane: TmuxPaneInfo, minPaneWidth: number = MIN_PANE_WIDTH): boolean {
-	return canSplitPaneAnyDirectionWithMinWidth(pane, minPaneWidth)
-}
-
-export function canSplitPaneAnyDirectionWithMinWidth(
+export function canSplitPaneAnyDirection(
 	pane: TmuxPaneInfo,
-	minPaneWidth: number = MIN_PANE_WIDTH,
+	minPaneWidth?: number,
 ): boolean {
-	return pane.width >= minSplitWidthFor(minPaneWidth) || pane.height >= MIN_SPLIT_HEIGHT
+	return pane.width >= getMinSplitWidth(minPaneWidth) || pane.height >= MIN_SPLIT_HEIGHT
 }
 
 export function getBestSplitDirection(
 	pane: TmuxPaneInfo,
-	minPaneWidth: number = MIN_PANE_WIDTH,
+	minPaneWidth?: number,
 ): SplitDirection | null {
-	const canH = pane.width >= minSplitWidthFor(minPaneWidth)
+	const canH = pane.width >= getMinSplitWidth(minPaneWidth)
 	const canV = pane.height >= MIN_SPLIT_HEIGHT
 
 	if (!canH && !canV) return null