fix(tmux-subagent): enable 2D grid layout with divider-aware calculations

- Account for tmux pane dividers (1 char) in all size calculations
- Reduce MIN_PANE_WIDTH from 53 to 52 to fit 2 columns in standard terminals
- Fix enforceMainPaneWidth to use (windowWidth - divider) / 2
- Add virtual mainPane handling for close-spawn eviction loop
- Add comprehensive decision-engine tests (23 test cases)

src/features/tmux-subagent/pane-state-querier.ts

@@ -3,15 +3,10 @@ import type { WindowState, TmuxPaneInfo } from "./types"
 import { getTmuxPath } from "../../tools/interactive-bash/utils"
 import { log } from "../../shared"
 
-/**
- * Query the current window state from tmux.
- * This is the source of truth - not our internal cache.
- */
 export async function queryWindowState(sourcePaneId: string): Promise<WindowState | null> {
   const tmux = await getTmuxPath()
   if (!tmux) return null
 
-  // Get window width and all panes in the current window
   const proc = spawn(
     [
       tmux,
@@ -19,7 +14,7 @@ export async function queryWindowState(sourcePaneId: string): Promise<WindowStat
       "-t",
       sourcePaneId,
       "-F",
-      "#{pane_id},#{pane_width},#{pane_left},#{pane_title},#{pane_active},#{window_width}",
+      "#{pane_id},#{pane_width},#{pane_height},#{pane_left},#{pane_top},#{pane_title},#{pane_active},#{window_width},#{window_height}",
     ],
     { stdout: "pipe", stderr: "pipe" }
   )
@@ -36,33 +31,43 @@ export async function queryWindowState(sourcePaneId: string): Promise<WindowStat
   if (lines.length === 0) return null
 
   let windowWidth = 0
+  let windowHeight = 0
   const panes: TmuxPaneInfo[] = []
 
   for (const line of lines) {
-    const [paneId, widthStr, leftStr, title, activeStr, windowWidthStr] = line.split(",")
+    const [paneId, widthStr, heightStr, leftStr, topStr, title, activeStr, windowWidthStr, windowHeightStr] = line.split(",")
     const width = parseInt(widthStr, 10)
+    const height = parseInt(heightStr, 10)
     const left = parseInt(leftStr, 10)
+    const top = parseInt(topStr, 10)
     const isActive = activeStr === "1"
     windowWidth = parseInt(windowWidthStr, 10)
+    windowHeight = parseInt(windowHeightStr, 10)
 
-    if (!isNaN(width) && !isNaN(left)) {
-      panes.push({ paneId, width, left, title, isActive })
+    if (!isNaN(width) && !isNaN(left) && !isNaN(height) && !isNaN(top)) {
+      panes.push({ paneId, width, height, left, top, title, isActive })
     }
   }
 
-  // Sort panes by left position (leftmost first)
-  panes.sort((a, b) => a.left - b.left)
+  panes.sort((a, b) => a.left - b.left || a.top - b.top)
 
-  // The main pane is the leftmost pane (where opencode runs)
-  // Agent panes are all other panes to the right
-  const mainPane = panes.find((p) => p.paneId === sourcePaneId) ?? panes[0] ?? null
-  const agentPanes = panes.filter((p) => p.paneId !== mainPane?.paneId)
+  const mainPane = panes.find((p) => p.paneId === sourcePaneId)
+  if (!mainPane) {
+    log("[pane-state-querier] CRITICAL: sourcePaneId not found in panes", {
+      sourcePaneId,
+      availablePanes: panes.map((p) => p.paneId),
+    })
+    return null
+  }
+
+  const agentPanes = panes.filter((p) => p.paneId !== mainPane.paneId)
 
   log("[pane-state-querier] window state", {
     windowWidth,
-    mainPane: mainPane?.paneId,
+    windowHeight,
+    mainPane: mainPane.paneId,
     agentPaneCount: agentPanes.length,
   })
 
-  return { windowWidth, mainPane, agentPanes }
+  return { windowWidth, windowHeight, mainPane, agentPanes }
 }