fix(cmd): respect SetStdin/SetStdout/SetStderr for tea.Exec compatibility

[puneet-chandna]

This PR fixes issue #506 where Bubble Tea programs running under Wish's bubbletea.Middleware with ssh.AllocatePty() would not properly release the alternate screen when executing child processes via tea.Exec.

Problem

When using tea.Exec with wish.Command, the child process output appeared "stacked" below the TUI instead of replacing it. This happened because wish.Cmd's SetStdin, [SetStdout](cci:1: wish/cmd.go:76:0-79:1), and SetStderr methods were no-ops, causing Bubble Tea's alt screen escape sequences to be written to a different output path than the child process.

Solution

Modified wish.Cmd to properly store and use the I/O handles set by Bubble Tea's exec flow:

• Added stdin, stdout, stderr fields to [Cmd](cci:2 /wish/cmd.go:31:0-37:1) struct
• Implemented [SetStdin](cci:1 /wish/cmd.go:71:0-74:1), [SetStdout](cci: wish/cmd.go:76:0-79:1), SetStderr to store values
• Updated [doRun()](cci: wish/cmd_unix.go:7:0-34:1) to use custom I/O when set, falling back to PTY otherwise

Changes

• [cmd.go](cci:7: /wish/cmd.go:0:0-0:0) - Added stdio fields and implemented Set* methods
• [cmd_unix.go](cci:7: wish/cmd_unix.go:0:0-0:0) - Use custom I/O when any handle is set
• cmd_windows.go - Use custom I/O when ALL handles are set (no ppty.Slave on Windows)
• [cmd_test.go](cci:7: wish/cmd_test.go:0:0-0:0) - Added [TestCommandSetStdio](cci:1: wish/cmd_test.go:100:0-138:1) to verify the fix

Testing

• All existing tests pass
• Added new test [TestCommandSetStdio](cci:1: wish/cmd_test.go:100:0-138:1) that verifies custom I/O handles are used

Before/After

Before: Child process output appears below TUI frame; scrollback shows "stacked" output
After: Child process replaces TUI cleanly; alt screen properly exits/enters around exec

Fixes #506

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.75%. Comparing base (ee243c6) to head (ee33d17).
⚠️ Report is 264 commits behind head on main.

❗ There is a different number of reports uploaded between BASE (ee243c6) and HEAD (ee33d17). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (ee243c6)	HEAD (ee33d17)
	2	1

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #522      +/-   ##
==========================================
- Coverage   77.23%   68.75%   -8.49%     
==========================================
  Files          19       22       +3     
  Lines         940      976      +36     
==========================================
- Hits          726      671      -55     
- Misses        160      250      +90     
- Partials       54       55       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[aymanbagabas]

Hey, this looks good! Could you look at our x/xpty library and use it to spawn the process instead?

[puneet-chandna]

@aymanbagabas Thanks for the suggestion! I’ve updated the implementation to use the x/xpty library for spawning the process. Please let me know if this matches what you had in mind.

[puneet-chandna]

Hi! Just a gentle follow-up on this PR. I’ve addressed the requested changes (switched process spawning to x/xpty) and CI is passing. Whenever you have time, I’d appreciate a re-review. Thanks!

[aymanbagabas]

Looks good! Could you back port this to the v2-exp branch in a separate PR?

[puneet-chandna]

I’ve opened a backport PR targeting the v2-exp branch with the same changes. Thanks!