[kattni]

Adds a "console output" mode to the iOS launcher (main.m) so Briefcase can capture Python output when it runs an app on a physical device.

When Briefcase runs an app on a physical device (beeware/briefcase#860), it launches it with xcrun devicectl device process launch --console and reads the process's console to detect test results and errors. Python's sys.stdout and sys.stderr are written to the Apple system log, though, so print() output never shows up there; only the launcher's NSLog lines do.

The contract

If the environment variable BRIEFCASE_CONSOLE_OUTPUT is set to 1 when the app launches, Python's sys.stdout and sys.stderr write to the process's real stdout and stderr (file descriptors 1 and 2) instead of the system log. Briefcase passes this in the --environment-variables argument to devicectl. Any other value, or no value, keeps the current behavior, so simulator logging and normal launches are unaffected. In console mode the launcher logs one extra line: Python stdout and stderr will be written to the console. All existing NSLog messages stay as they are.

Implementation

• Python 3.14+: config.use_system_logger is now set to !console_output instead of always 1.
• Python 3.11–3.13: there is no config field for this. On iOS, _apple_support.init_streams() always replaces sys.stdout and sys.stderr with SystemLog wrappers during startup (all three support packages ship _apple_support.py). In console mode, the launcher runs a short PyRun_SimpleString after Py_InitializeFromConfig that rebinds sys.stdout and sys.stderr to sys.__stdout__ and sys.__stderr__. Those are the original UTF-8 streams on fds 1 and 2, unbuffered because of config.buffered_stdio = 0. If that call fails, the crash dialog is shown and the app exits.

Verification

I generated a probe app from this branch with Briefcase 0.4.7 for Python 3.13 (support b18) and 3.14, built it for the iPhone 16 simulator, and launched it with xcrun simctl launch --console-pty. The probe prints repr(sys.stdout) to stdout and repr(sys.stderr) to stderr, then raises SystemExit(0).

Python	BRIEFCASE_CONSOLE_OUTPUT	Console	System log (log show)
3.13	unset	NSLog lines only	<SystemLog (level 0)> / <SystemLog (level 16)>
3.13	1	<_io.TextIOWrapper name='<stdout>' ... encoding='utf-8'> and <stderr>	no probe lines
3.14	unset	NSLog lines only	<SystemLog (level 0)> / <SystemLog (level 16)>
3.14	1	<_io.TextIOWrapper name='<stdout>' ... encoding='utf-8'> and <stderr>	no probe lines

On the simulator the variable was passed as SIMCTL_CHILD_BRIEFCASE_CONSOLE_OUTPUT=1. I did not test Python 3.11, 3.12, or 3.15 directly: 3.11 and 3.12 use the same _apple_support path as 3.13, and 3.15 uses the same use_system_logger path as 3.14. I also haven't run this on a physical device yet; that will happen through the Briefcase side of #860.

Refs beeware/briefcase#860

PR Checklist:

• I will abide by the BeeWare Code of Conduct
• I have read and have followed the CONTRIBUTING.md file
• This PR was generated or assisted using an AI tool

Assisted-by: Claude Code (Claude Opus 5.5)