refactor(desktop): split WindowLatexPdfMixin into compile + pdf-preview (Batch 10 Stage 3)

[yilibinbin]

Batch 10 — Stage 3: split WindowLatexPdfMixin (behavior-preserving)

The cleanest, lowest-risk split from the reviewed decomposition plan, backstopped
by the Stage 0 guardrails (merged in #81). Two commits:

1/2 — extract the two LaTeX QThread workers to workers_qt.py.
_TectonicInstallWorker and _LatexCompileWorker (+ their helpers:
_TECTONIC_STAGE_LABELS, _LatexEngineRun, _LatexCompileOutcome,
_looks_like_plain_tex_output) were the only workers defined inside a mixin file;
every other worker (CalcWorker, FitWorker, RootSolvingWorker, …) lives in
workers_qt.py. Moved for architectural consistency (Gemini review finding).

2/2 — split the mixin via the proven window_fitting_mixin shim pattern.

• window_latex_compile_mixin.py — WindowLatexCompileMixin (open/save/reload,
  compile_latex_to_pdf, engine resolution, tectonic install).
• window_pdf_preview_mixin.py — WindowPdfPreviewMixin (PDF render/zoom/image
  display, dark-mode inversion).
• window_latex_pdf_mixin.py — now a 66-line shim (was 969): empty subclass
  composing the two (compile leftmost), re-exporting WindowLatexPdfMixin and
  the two workers, so all existing imports keep working unchanged.

Guardrails updated deliberately: _EXPECTED_MRO expands the shim into its two
sub-mixins; the 6 composition guardrails still pass (no mixin __init__, no Qt
event override, no cross-sibling duplicate names). window_latex_pdf_mixin.py
dropped from the file-size ratchet (969 → 66); workers_qt.py consciously
baselined at 807.

Test plan

• Independently re-verified (not the subagent's self-report): ruff clean,
  public import + full MRO check pass.
• Full suite: 3817 passed, 9 skipped, 0 failed.

Stage 1 (statistics, larger) is a possible future PR; Stage 2 (cross-family run
controller) and Stage 4 (Protocol) are NO-GO per the two-model review.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • Added LaTeX-to-PDF compilation from the desktop app, including open, save, reload, and open-generated-PDF actions.
  • Added a richer PDF preview with multi-page rendering, zoom controls, and dark-mode support.
  • Added guided setup for missing LaTeX tools, including Tectonic installation prompts and progress feedback.

• Bug Fixes

  • Improved handling of compile cancellation, timeouts, and error states.
  • Added automatic fallback behavior when a compiler run fails in common cases.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: d75209d2-22f6-4d94-b23b-4a7cdabb1978

📥 Commits

Reviewing files that changed from the base of the PR and between daa77fd and c412c11.

📒 Files selected for processing (8)

• app_desktop/window_latex_compile_mixin.py
• app_desktop/window_latex_pdf_mixin.py
• app_desktop/window_pdf_preview_mixin.py
• app_desktop/workers_qt.py
• tests/test_desktop_latex_compile_ui.py
• tests/test_file_size_ratchet.py
• tests/test_qfiledialog_titles_bilingual.py
• tests/test_window_mixin_composition_guardrails.py

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📝 Walkthrough

Walkthrough

The monolithic window_latex_pdf_mixin.py is split into window_latex_compile_mixin.py (compilation orchestration, engine resolution, Tectonic install) and window_pdf_preview_mixin.py (PDF rendering, zoom, dark mode). Worker classes move to workers_qt.py. The original file becomes a thin composing shim. Tests and baselines are updated accordingly.

Changes

LaTeX compile/preview mixin split

Layer / File(s)	Summary
LaTeX/Tectonic worker classes app_desktop/workers_qt.py	Adds _TectonicInstallWorker, _LatexCompileWorker, _LatexEngineRun/_LatexCompileOutcome dataclasses, stage labels, and plain-TeX detection heuristic; exports them via __all__.
Compile orchestration and engine resolution app_desktop/window_latex_compile_mixin.py	New WindowLatexCompileMixin with compile_latex_to_pdf, completion handling, open_compiled_pdf, editor persist/reload, engine resolution tiers, and Tectonic install prompting.
PDF preview rendering, zoom, dark mode app_desktop/window_pdf_preview_mixin.py	New WindowPdfPreviewMixin with zoom management, base image generation via external tools, page display, and dark-mode inversion.
Composing shim app_desktop/window_latex_pdf_mixin.py	Old inline implementation replaced with an empty class composing the two new mixins and re-exporting worker symbols for backward compatibility.
Test and baseline updates tests/test_desktop_latex_compile_ui.py, tests/test_qfiledialog_titles_bilingual.py, tests/test_window_mixin_composition_guardrails.py, tests/test_file_size_ratchet.py	Patch targets, bilingual title checks, MRO expectations, and file-size baselines updated to match the new module layout.

Estimated code review effort: 4 (Complex) | ~60 minutes

Sequence Diagram(s)

sequenceDiagram
  participant User
  participant CompileMixin as WindowLatexCompileMixin
  participant CompileWorker as _LatexCompileWorker
  participant TectonicWorker as _TectonicInstallWorker
  participant PreviewMixin as WindowPdfPreviewMixin

  User->>CompileMixin: compile_latex_to_pdf()
  CompileMixin->>CompileMixin: _persist_latex_editor()
  CompileMixin->>CompileMixin: _ensure_latex_engine()
  alt Tectonic missing
    CompileMixin->>TectonicWorker: _offer_tectonic_install()
    TectonicWorker-->>CompileMixin: EngineChoice or None
  end
  CompileMixin->>CompileWorker: start(engine)
  CompileWorker-->>CompileMixin: completed(outcome)
  CompileMixin->>PreviewMixin: _render_pdf_preview(force_reload=True)
  PreviewMixin-->>User: display rendered PDF pages

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Related PRs: No related pull requests identified from the provided information.

Suggested labels: refactor, desktop-app, latex

Suggested reviewers: yilibinbin

🐰 A mixin split, tidy and neat,
Compile and preview, each finds its seat,
Workers now live in a shared little home,
Tectonic installs while the tests learn to roam,
A shim ties it all with a whisker-light thread. 🥕

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main refactor: splitting WindowLatexPdfMixin into compile and PDF preview responsibilities.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/batch10-stage3

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