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

src/features/tmux-subagent/tmux-grid-constants.ts

@@ -1,6 +1,8 @@
 import { MIN_PANE_HEIGHT, MIN_PANE_WIDTH } from "./types"
+import type { CapacityConfig } from "./types"
 
 export const MAIN_PANE_RATIO = 0.5
+const DEFAULT_MAIN_PANE_SIZE = MAIN_PANE_RATIO * 100
 export const MAX_COLS = 2
 export const MAX_ROWS = 3
 export const MAX_GRID_SIZE = 4
@@ -8,3 +10,48 @@ export const DIVIDER_SIZE = 1
 
 export const MIN_SPLIT_WIDTH = 2 * MIN_PANE_WIDTH + DIVIDER_SIZE
 export const MIN_SPLIT_HEIGHT = 2 * MIN_PANE_HEIGHT + DIVIDER_SIZE
+
+function clamp(value: number, min: number, max: number): number {
+	return Math.max(min, Math.min(max, value))
+}
+
+export function getMainPaneSizePercent(config?: CapacityConfig): number {
+	return clamp(config?.mainPaneSize ?? DEFAULT_MAIN_PANE_SIZE, 20, 80)
+}
+
+export function computeMainPaneWidth(
+	windowWidth: number,
+	config?: CapacityConfig,
+): number {
+	const safeWindowWidth = Math.max(0, windowWidth)
+	if (!config) {
+		return Math.floor(safeWindowWidth * MAIN_PANE_RATIO)
+	}
+
+	const dividerWidth = DIVIDER_SIZE
+	const minMainPaneWidth = config?.mainPaneMinWidth ?? Math.floor(safeWindowWidth * MAIN_PANE_RATIO)
+	const minAgentPaneWidth = config?.agentPaneWidth ?? MIN_PANE_WIDTH
+	const percentageMainPaneWidth = Math.floor(
+		(safeWindowWidth - dividerWidth) * (getMainPaneSizePercent(config) / 100),
+	)
+	const maxMainPaneWidth = Math.max(0, safeWindowWidth - dividerWidth - minAgentPaneWidth)
+
+	return clamp(
+		Math.max(percentageMainPaneWidth, minMainPaneWidth),
+		0,
+		maxMainPaneWidth,
+	)
+}
+
+export function computeAgentAreaWidth(
+	windowWidth: number,
+	config?: CapacityConfig,
+): number {
+	const safeWindowWidth = Math.max(0, windowWidth)
+	if (!config) {
+		return Math.floor(safeWindowWidth * (1 - MAIN_PANE_RATIO))
+	}
+
+	const mainPaneWidth = computeMainPaneWidth(safeWindowWidth, config)
+	return Math.max(0, safeWindowWidth - DIVIDER_SIZE - mainPaneWidth)
+}