fix(tmux): avoid Bun global in runner bundle

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

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

src/shared/bun-spawn-shim.ts

@@ -14,6 +14,7 @@ export interface SpawnOptions {
   stderr?: StdioMode
   stdio?: StdioTuple
   detached?: boolean
+  signal?: AbortSignal
 }
 
 export interface SpawnedProcess {
@@ -138,6 +139,7 @@ export function spawn(cmdOrOpts: unknown, opts?: unknown): SpawnedProcess {
     env: options.env,
     stdio: resolveStdio(options),
     detached: options.detached,
+    signal: options.signal,
   })
 
   return wrapNodeProcess(proc)

src/shared/tmux/runner.ts

@@ -1,4 +1,4 @@
-import { spawn } from "bun"
+import { spawn } from "../bun-spawn-shim"
 
 type RunTmuxOptions = {
 	retry?: number