fix(core): make shell tool work under Bun

[euxaristia]

Summary

Two related runtime issues prevented bun-launched builds of gemini-cli from running shell tool calls. The first failure visible to a user is an ioctl(2) failed, EBADF crash inside a React useEffect. After patching that, the shell tool stops crashing but every command returns empty output. Both stem from @lydell/node-pty not behaving correctly when loaded by Bun.

• No output under Bun. getPty() now short-circuits to the existing child_process fallback when process.versions.bun is set. The fallback path already has Bun-specific handling (detached:false to avoid immediate SIGHUP, added in fix(core): disable detached mode in Bun to prevent immediate SIGHUP of child processes google-gemini/gemini-cli#22620). GEMINI_PTY_INFO=node-pty overrides the new behavior for anyone wanting to test the pty path under Bun.
• ioctl(2) failed, EBADF crash on resize. ShellExecutionService.onExit calls destroyPtyProcess() (which closes the master fd) before the entry is removed from activePtys at the end of the cleanupLogStream promise chain. A concurrent resizePty() from ShellToolMessage's useEffect lands in that window, calls the native resize on a closed fd, and ioctl returns EBADF. The window is narrow under Node but widens under Bun's microtask scheduling. resizePty() now treats EBADF/ENOTTY the same way it already treats ESRCH and the Windows "Cannot resize a pty that has already exited" message — the pty is gone, nothing to resize.

The two fixes are independent but both required: the fallback gating prevents the bad state from being entered under Bun, the resize guard makes the race safe everywhere in case a stray pty path is hit (manual GEMINI_PTY_INFO=node-pty testing, future runtimes with similar timing).

Test plan

• bun start no longer crashes with ioctl(2) failed, EBADF on shell tool calls
• Shell tool calls under bun start produce captured output (e.g. echo hello, bun --version, which bun)
• Existing behavior unchanged under Node: pty path still selected, no new code runs on the hot path
• GEMINI_PTY_INFO=node-pty bun start re-enables the pty path (still broken under Bun, but useful for confirming the override works)
• New unit test should ignore EBADF when the master fd was already closed covers the resize swallow

🤖 Generated with Claude Code

[gemini-code-assist]

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