TWO MUTATIONS LEFT BOTH B4 ROWS GREEN. Changing the source to
`Clipboard`, or replacing the dispatch arm with a no-op, was invisible:
one row asserted `middle_click_paste_source` in isolation and the other
asserted `route_pointer` in isolation, and nothing asserted the effect
the gesture produces. Two seams tested separately are not a path tested
once.
A third row drives a middle press through `dispatch_window_event` and
asserts EXACTLY ONE outbound `Paste` carrying the PRIMARY payload, and
that the release sends none. PRIMARY and CLIPBOARD are stubbed with
DISTINGUISHABLE contents, which is the point --- identical stubs would
pass with the wrong selection read.
That needed a seam: `State::set_test_selection`, consulted by
`read_os_selection` before the OS clipboard. A test-only field in
production code is a cost, and it is the smallest one that makes B4's
actual contract --- WHICH selection --- assertable without a real
clipboard. Both mutations now fire: source-to-Clipboard fires two rows,
the no-op dispatch fires the end-to-end row.
AND THE OFF-LINUX FALLBACK WAS UNFRAMED BEHAVIOUR I INVENTED. B4 rules
"PRIMARY on Linux" and rules nothing else. The gesture was inert on
every other platform; my previous commit made it paste the CLIPBOARD
there, and the row adopted that choice permanently. `middle_click_paste_source`
now returns `Option`, `None` off Linux, and the gesture stays inert. A
fallback needs framing and re-approval, not a default chosen while
implementing.
Levi Neuwirth
3a4a748316