TextLayerBuilder: global selection listeners are never re-bound after the viewer that registered them is aborted while another text layer is alive #22129

Version: pdfjs-dist 6.3.289 (same code on master, web/text_layer_builder.js, checked against v6.4.299)

Setup: two PDFViewer instances on one page, each created with its own abortSignal (for example a page reader plus a modal reader).

Steps

1. Mount viewer A with abortSignal: a.signal and render a page with a text layer.
2. Mount viewer B with abortSignal: b.signal and render a page with a text layer.
3. Abort a (viewer A is torn down; viewer B stays).
4. In viewer B, press the mouse on the text layer, drag, release.

Expected: the selection works, and on pointerup the text layer drops its selecting class.

Actual: after the first mousedown, the text layer keeps selecting. With the stock CSS, .textLayer.selecting .endOfContent { top: 0 } makes endOfContent cover the whole layer (user-select: none), and .textLayer.selecting ~ .annotationLayer section { pointer-events: none } disables the link annotations. New drag selections and links on that page stop working until every text layer is gone.

Cause: #enableGlobalSelectionListener(globalAbortSignal) binds the document listeners (pointerdown, pointerup, blur, keyup, selectionchange) on AbortSignal.any([#selectionChangeAC.signal, globalAbortSignal]), where globalAbortSignal is the signal of the FIRST viewer that registered a text layer. It returns early while #selectionChangeAC is set, and #selectionChangeAC is cleared only when #textLayers.size === 0. When the first viewer's signal aborts, the listeners go away, but #selectionChangeAC stays set because viewer B's text layer is still in #textLayers, so no later call binds them again.

Possible fix: the shared listeners should not live on one viewer's signal. For example, keep each text layer's abortSignal beside its endOfContent in #textLayers; when the signal the listeners were bound with aborts, drop that viewer's layers, clear #selectionChangeAC, and if text layers remain, bind again with a remaining layer's signal. Checking only #selectionChangeAC's own signal at the next #bindMouse is not enough: the surviving viewer's existing layers never call #bindMouse again.