diff --git a/.config/opencode/plugins/tmux-panes.ts b/.config/opencode/plugins/tmux-panes.ts
index 9fe12a7..236a0dc 100644
--- a/.config/opencode/plugins/tmux-panes.ts
+++ b/.config/opencode/plugins/tmux-panes.ts
@@ -1,5 +1,6 @@
 import type { Plugin } from "@opencode-ai/plugin"
 import { spawn } from "bun"
+import { appendFileSync } from "fs"
 
 /**
  * tmux-panes plugin
@@ -13,8 +14,14 @@ import { spawn } from "bun"
  *   - Panes close automatically when subagent sessions end
  *
  * Only activates when running inside a tmux session (TMUX env var is set).
+ *
+ * Debug log: /tmp/opencode-tmux-debug.log
  */
 
+const DEBUG_LOG = "/tmp/opencode-tmux-debug.log"
+const log = (msg: string) =>
+	appendFileSync(DEBUG_LOG, `[${new Date().toISOString()}] ${msg}\n`)
+
 const isInsideTmux = () => Boolean(process.env.TMUX)
 const getCurrentPaneId = () => process.env.TMUX_PANE
 
@@ -23,7 +30,8 @@ const plugin: Plugin = async (ctx) => {
 
 	const sessions = new Map<string, string>() // sessionId → tmux paneId
 	const sourcePaneId = getCurrentPaneId()
-	const serverUrl = ctx.serverUrl.toString()
+	const serverUrl = ctx.serverUrl?.toString() ?? ""
+	log(`plugin init — serverUrl=${serverUrl} sourcePaneId=${sourcePaneId}`)
 
 	// Ordered list of pane IDs in the right column.
 	// Empty = no right column yet; length > 0 = right column exists.
@@ -39,7 +47,11 @@ const plugin: Plugin = async (ctx) => {
 				const sessionId: string = info.id
 				if (sessions.has(sessionId)) return
 
-				const cmd = `opencode attach ${serverUrl} --session ${sessionId}`
+				// Wrap the attach command: on failure, show the error and keep the
+			// pane open for 30 s so we can read it before it disappears.
+			const attachCmd = `opencode attach ${serverUrl} --session ${sessionId}`
+			const cmd = `bash -c '${attachCmd}; _exit=$?; echo "--- exit: $_exit ---" >> ${DEBUG_LOG}; [ $_exit -ne 0 ] && sleep 30'`
+			log(`spawning pane — cmd: ${attachCmd}`)
 
 				let args: string[]
 				if (rightColumnPanes.length === 0) {
@@ -76,10 +88,12 @@ const plugin: Plugin = async (ctx) => {
 
 				const proc = spawn(args, { stdout: "pipe", stderr: "pipe" })
 				const paneId = (await new Response(proc.stdout).text()).trim()
-				if ((await proc.exited) === 0 && paneId) {
-					sessions.set(sessionId, paneId)
-					rightColumnPanes.push(paneId)
-				}
+			const exitCode = await proc.exited
+			log(`split-window exit=${exitCode} paneId=${paneId}`)
+			if (exitCode === 0 && paneId) {
+				sessions.set(sessionId, paneId)
+				rightColumnPanes.push(paneId)
+			}
 			}
 
 			// Kill the pane when the subagent session ends