Follow-up to commit 14a. The booru logger has only the in-app
QTextEdit LogHandler attached (main_window.py:436-440), so the
POPOUT_FSM dispatch trace from the state machine adapter only
reaches the Ctrl+L log panel — invisible from the shell.
Adds a stderr StreamHandler attached directly to the
`booru.popout.adapter` logger so:
python -m booru_viewer.main_gui 2>&1 | grep POPOUT_FSM
works during the commit-14a verification gate. The user can capture
the dispatch trace per scenario and compare it to the legacy path's
actions before commit 14b switches authority.
The handler is tagged with a `_is_popout_fsm_stderr` sentinel
attribute so re-imports of window.py don't stack duplicate
handlers (defensive — module-level code only runs once per process,
but the check costs nothing).
Format: `[HH:MM:SS.mmm] POPOUT_FSM <event> | <old> -> <new> | effects=[...]`
The millisecond precision matters for the seek scenario where the
race window is sub-100ms.
Propagation to the parent booru logger is left enabled, so dispatch
trace lines also continue to land in the in-app log panel for the
user who prefers Ctrl+L.
Tests still pass (81 / 81). No behavior change to widgets — this
only affects log output routing.
pax
35d80c32f2