theme(fix[spa-nav]): fragment scroll + copy-button recreation

[tony]

Fixes #19 (fragment scroll). Also folds in two related SPA-nav defects surfaced while testing the scroll fix end-to-end.

Bugs fixed

1. Cross-page fragment links don't scroll to anchor

document.querySelector(hash) mis-parses dotted IDs. Python autodoc anchors like #libtmux_mcp.models.SearchPanesResult read as id libtmux_mcp AND class models AND class SearchPanesResult — never match. Every py:class / py:meth / py:attr cross-ref silently failed to scroll.

Scroll gated behind !isPop. The popstate listener calls navigate(..., true), so browser back/forward to a fragment URL never scrolled. gp-sphinx's own fetch+swap bypasses browser-native scroll restoration.

2. Copy buttons disappear after SPA swap from a page with no .copybtn

addCopyButtons cloned an existing .copybtn as its template. Landing pages and prose-only indexes have no code blocks, so copyBtnTemplate stayed null forever. SPA-navigating to any code-block page from there rendered without copy buttons.

3. Copy buttons only re-applied to div.highlight pre

addCopyButtons hard-coded that selector, ignoring whatever the project configured via copybutton_selector (e.g. prompt admonitions). Projects using custom selectors lost those copy affordances on every SPA swap.

Fix

packages/sphinx-gp-theme/src/sphinx_gp_theme/theme/static/js/spa-nav.js:

• Scroll: querySelector(hash) → getElementById(decodeURIComponent(hash.slice(1))); hash branch moved out of !isPop guard so popstate with fragment scrolls.
• Copy buttons: inline HTML template matching sphinx-copybutton's output verbatim (same classes, same SVG). Initial page no longer needs any .copybtn for SPA to work.
• Copy buttons: iterate window.GP_SPHINX_COPYBUTTON_SELECTOR || "div.highlight pre" so project-configured selectors are respected.

packages/gp-sphinx/src/gp_sphinx/config.py:

• New _inject_copybutton_bridge on html-page-context. Emits a small inline <script>window.GP_SPHINX_COPYBUTTON_SELECTOR=…;</script> from the project's copybutton_selector config. Gated on sphinx_copybutton being loaded.

Verification

Tested end-to-end against libtmux-mcp docs at localhost:8024 via Playwright MCP. libtmux-mcp configures copybutton_selector = "div.highlight pre, div.admonition.prompt > p:last-child" — it's a good test bed since it exercises both the fragment-scroll path and the extended-selector path.

Scenario	Result
SPA click → URL with #libtmux_mcp.models.SearchPanesResult	scrollY=9268, at anchor
Browser forward (popstate) → same fragment URL	scrollY=9268, at anchor
SPA click → fragment-less URL	scrollY=0, scrolled to top
Landing / (no code blocks) → SPA-nav to /installation/	11/11 <pre> get copy buttons
Landing / → SPA-nav to /recipes/ (prompts only)	8/8 prompt admonitions get copy buttons
Inline-generated button SVG class	icon-tabler-copy (matches sphinx-copybutton)

Obsoletes libtmux-mcp's docs/_static/js/spa-copybutton-reinit.js shim, which was a project-local workaround for Bugs 2 and 3. That shim is being removed in a follow-up commit in libtmux-mcp.

Test plan

• uv run ruff format --check .
• uv run ruff check .
• uv run mypy
• uv run pytest — all tests pass
• Manual: Playwright verification across all six scroll + copybutton scenarios above
• Reviewer sanity: open any gp-sphinx Python docs site whose landing page has no code blocks; SPA-nav to a code-block page and a prompt-admonition page; confirm copy buttons appear

Out of scope

• copybutton_image_svg config override — we hard-code sphinx-copybutton's default SVG. Projects that override the icon get the default SVG on SPA-swapped buttons until the initial sphinx-copybutton run repaints (which it won't, since it only runs on DOMContentLoaded). Acceptable for now.
• i18n tooltip — we hard-code "Copy" instead of sphinx-copybutton's {{ messages[locale]['copy'] }}. Non-English docs get English tooltips on SPA-swapped buttons. Acceptable for now; can be bridged later.
• No JS test harness in this repo; fix lacks a regression test. Adding one is a worthwhile follow-up but intentionally deferred.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 37.50000% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.31%. Comparing base (f702425) to head (8361afa).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/gp-sphinx/src/gp_sphinx/config.py	37.50%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #20      +/-   ##
==========================================
- Coverage   90.34%   90.31%   -0.04%     
==========================================
  Files         147      147              
  Lines       12597    12605       +8     
==========================================
+ Hits        11381    11384       +3     
- Misses       1216     1221       +5     

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