Phase 4 of REVIEWS/DART_PDF_VS_MAKEPAD_PDF_GAP_ANALYSIS.md. The previous
commit added the interaction logic but left it an orphan: nothing routed
Makepad events into it, which is the exact defect the review names when it
says PdfPageView declares is_interactive() -> false and an empty
handle_event.
New pdf-makepad/src/page_view.rs, PdfPageWidget:
- is_interactive() returns true and handle_event routes real events.
- Step 4.1 ordering: form field events, then annotation hit testing, then
text selection. The order is enforced inside InteractionState::click so
it cannot drift between the widget and the tests.
- Step 4.2: link underlines and form widget borders are drawn, and the
cursor changes over links and text fields.
- Step 4.3: field values draw inside their widget rects, a focused field is
highlighted and shows its uncommitted buffer.
- Step 4.4: navigation is emitted as PdfPageAction to the host. The widget
never opens a URL (rule 5).
- Key focus loss commits the pending edit, so an edit is never silently
lost, while Escape still abandons it.
- Only keys the editor handles are consumed; everything else falls through
to the host instead of being swallowed.
The widget keeps no decision logic of its own: it syncs the viewport from
its on-screen rect and delegates. That keeps the part that needs a live Cx
as small as possible, because it is the part that cannot be unit tested.
Also adds Selection to interaction.rs so drag-to-select and copy read
through the Phase 5 PageText API rather than re-deriving positions.
Tests: new tests/phase4_exit_criterion.rs drives the exit criterion against
the real two-page AcroForm fixture, not synthetic dictionaries. Click a link
gives OpenUri; click a field, type, commit, and the value changes, the
appearance regenerates with the new text and the draw list shows it. It also
asserts an abandoned edit changes nothing, the checkbox uses the /On state
declared in the file, and form fields route before annotations.
Validation: TEST_TARGET=pdf-ui ./tools/test-rust-clean.sh
202 tests pass; rustfmt and clippy -D warnings clean.
