ci: expose native Qt crashes and stalled test stacks

[lukisch]

Native GUI tests on #3 abort on Linux and macOS; a Windows job reports 361 passed and 1 skipped before exiting unsuccessfully. The macOS smoke process also exits with SIGSEGV before buffered output is retained. The root cause remains unknown.

Enable Python faulthandler and unbuffered output for the existing test and smoke commands. Disable pytest output capture and emit diagnostic stacks after a test runs for 60 seconds. This timeout prints stacks; it does not terminate tests or change their assertions, exit status, job deadlines, dependencies or OS/Python matrix.

Based directly on unchanged main 69e312c, independent of #3. This diagnostic PR can establish baseline behavior with current dependencies; it is not a product fix or evidence that #3 caused the crashes.

Validation: all four workflow YAML files parse; git diff --check passes; only four command lines in two workflows changed. Native CI results remain pending. A separate Windows baseline smoke passes with isolated temp/settings/plugin paths; that does not establish native macOS acceptance.

Author model: gpt-6.1-sol (Codex). Independent review pending. Draft only; merges disabled. No release or runtime mirror change.

The current revision adds a bounded Linux/Python3.11 comparison of PySide6_Essentials 6.11.2 and 6.12.0. It exercises an isolated QSyntaxHighlighter subclass through1000 document updates, reports callback counts and None references, and preserves native process failures. No product modules/settings/files are loaded; no product dependency is pinned. This probes a binding hypothesis, not a confirmed cause or repair.

Embedded Python and workflow YAML parse; local probe completes12000 callbacks on Windows/Python3.12.10/PySide6+shiboken6.11.1. This local run does not substitute for either native comparison cell. Earlier local Qt6.12 labels were not version-captured; the current test interpreter explicitly reports6.11.1. Native comparison results remain pending.

The first comparison attempt did not reach the probe: 6.11.3 was unavailable in the runner package index, and the 6.12.0 QtGui import lacked libEGL.so.1. The current revision uses index-confirmed 6.11.2 and installs libegl1/libgl1/libxkbcommon-x11-0 in the diagnostic jobs. These prerequisite failures do not support or refute the binding hypothesis. YAML, matrix and embedded Python validation pass; corrected native results pending.

[github-actions]

Welcome! 👋 Thanks for your first pull request in this repository.

A maintainer will review it soon. Please make sure:

• Your changes are tested
• Documentation is updated if needed
• The PR description explains what and why

Thanks for contributing!