PDF text selection misbehaviour (some glyphs unselectable, selections
jumping to other positions) is almost always caused by misalignment
between the visible canvas-rendered glyphs and the invisible text
layer that PDF.js overlays for selection. There's no way to see this
without devtools — which makes it hard for end users to tell whether
a specific PDF is OCR-noisy, has bad font fallbacks, or has no text
layer at all.
This adds a developer-facing toggle in the SessionMenu ("Debug text
layer") that:
- paints every text-layer span yellow with a blue outline so it's
obvious where text is selectable and where it isn't, and
- logs every onSelection event to the browser console with the
captured text, page, normalized rects, and the selectors the
pipeline derived from it.
Preference persists in localStorage under
`citation-evidence:debug:textLayer`. Surfaced via a new
`useDebugFlag()` hook in @work so the SessionMenu (app layer) and the
ViewerShell (work layer) can both subscribe without breaching the
boundary plugin.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
