[dccote]

Summary

Replaces `SpectraViewer.clickSave`'s native file-dialog with an in-figure `TextBox` widget. The user types the path inline; Save reads it directly. No platform file dialog is involved.

This fixes all three of the compounding bugs that surfaced while debugging the original "Save locks up very often" report:

1. Non-reentrant lock deadlock. `threading.Lock` was held by both `animate()` and `clickSave()`. Whenever matplotlib's animation timer fired during the save dialog, the timer callback ran on the same main thread holding the lock and deadlocked.

2. matplotlib 3.10 broke the macOS C dialog. `backend_macosx._macosx.choose_save_file` changed signature from 2 args to 3 between matplotlib versions. The old code's bare `except:` had hidden the resulting `TypeError` so the user saw "click Save, nothing happens".

3. Tk + macOS NSRunLoop = SIGSEGV. Falling back to `tkinter.filedialog.asksaveasfilename` segfaulted (exit 139). macOS only allows one NSRunLoop owner per main thread; matplotlib's `macosx` backend already owns it, and Tk's modal dialog tries to start a competing loop.

All three are run-loop-mixing failures. The fix sidesteps them by not invoking any second GUI toolkit during save.

Changes (`hardwarelibrary/spectrometers/viewer.py`)

• Add `self.filenameBox = TextBox(axFile, "File ", initial="spectrum.csv")` to the control row.
• `clickSave` now reads `self.filenameBox.text` directly and writes the CSV via `spectrometer.saveSpectrum(...)`. `try/finally` ensures the animation resumes even if the write raises.
• Drop `threading.Lock`, `matplotlib.backends as backends` import, and the `askForSavePath` helper — none are needed once the dialog is gone.
• Re-layout the control bar to fit the new TextBox: shrink button heights from 0.075 → 0.05, shorten the integration-time label to `"ms "`, widen the filename TextBox to ~0.30, push Time/Save/Quit to the right edge.

Net: +54 / −59 lines in one file.

Test plan

• Module imports cleanly (no stale references after the lock / backends / askForSavePath removal).
• Live viewer test with `DebugSpectro`: click Save with default filename → CSV is written. Click Save repeatedly → no lock-up, no segfault.
• Real-hardware test (Ocean Optics USB2000+): viewer runs, save works.
• Verify on Windows / Linux that the TextBox layout is reasonable (only tested on macOS).

Why a TextBox instead of switching backends

The other paths considered:

• Switch matplotlib backend to TkAgg. Tk and matplotlib would share one event loop. Works, but affects every figure the library produces, not just the spectrum viewer.
• Auto-save with timestamp filename. Reliable but takes filename-choice away from the user.
• Filename TextBox (this PR). Stays inside the existing `macosx` backend, no extra toolkit, gives the user inline editing of the path. Lowest blast radius.

🤖 Generated with Claude Code