Watch-mode line targets: narrow fsTree to the targeted files and apply their selectors for the whole session.

Watch is one page with one QUnit config, so a page-global selector set would filter every OTHER file's tests down to nothing on the next save — the per-file scoping concurrent mode gets from one-group-per-file has nowhere to live here. Narrowing fsTree keeps the selectors true for everything loaded, at the cost of dropping untargeted inputs; those are named rather than silently watched-but-never-run. qa clears the selectors to run everything still watched.

import type { Config } from '../../types.ts';
// Defined, not invoked: narrows config.fsTree/selectors for the whole watch session.
async function scopeWatchSession(config: Config) {
  await applyWatchLineTargets(config); // fsTree keeps only the `file#34`-targeted files
}