refactor(tmux-subagent): state-first architecture with decision engine (#1125)

* refactor(tmux-subagent): add state-first architecture with decision engine

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

* feat(tmux): add pane spawn callbacks for background and sync sessions

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

---------

Co-authored-by: justsisyphus <justsisyphus@users.noreply.github.com>
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

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

@@ -0,0 +1,68 @@
+import { spawn } from "bun"
+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,
+      "list-panes",
+      "-t",
+      sourcePaneId,
+      "-F",
+      "#{pane_id},#{pane_width},#{pane_left},#{pane_title},#{pane_active},#{window_width}",
+    ],
+    { stdout: "pipe", stderr: "pipe" }
+  )
+
+  const exitCode = await proc.exited
+  const stdout = await new Response(proc.stdout).text()
+
+  if (exitCode !== 0) {
+    log("[pane-state-querier] list-panes failed", { exitCode })
+    return null
+  }
+
+  const lines = stdout.trim().split("\n").filter(Boolean)
+  if (lines.length === 0) return null
+
+  let windowWidth = 0
+  const panes: TmuxPaneInfo[] = []
+
+  for (const line of lines) {
+    const [paneId, widthStr, leftStr, title, activeStr, windowWidthStr] = line.split(",")
+    const width = parseInt(widthStr, 10)
+    const left = parseInt(leftStr, 10)
+    const isActive = activeStr === "1"
+    windowWidth = parseInt(windowWidthStr, 10)
+
+    if (!isNaN(width) && !isNaN(left)) {
+      panes.push({ paneId, width, left, title, isActive })
+    }
+  }
+
+  // Sort panes by left position (leftmost first)
+  panes.sort((a, b) => a.left - b.left)
+
+  // 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)
+
+  log("[pane-state-querier] window state", {
+    windowWidth,
+    mainPane: mainPane?.paneId,
+    agentPaneCount: agentPanes.length,
+  })
+
+  return { windowWidth, mainPane, agentPanes }
+}