Merge master, dedupe the kept copy, and retire superseded switches

Master had moved ten commits ahead. Two conflicts, both resolved without
losing either side: the `XTREAM_PROBE_URL` handler this PR extracted into
`events/stream-probe.ts` stays extracted (master added performance capture
nearby but never touched that handler), and the mock-server scenario table
takes the union of master's `performance` row and this branch's `multisrc`
pair.

Two findings fixed alongside it.

Pinning the copy the route is already on makes discovery return that very
row, so prepending the current source listed one stream twice — a phantom
copy in the grouping and a chip that counted it.

And handing the "playing" badge back to the route row left an in-flight
switch valid, so a slow resolution could arrive afterwards and replace the
playback the user had just started with Play, Resume or Restart.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/architecture/vod-multi-source.md

@@ -248,7 +248,10 @@ for "Up".
 One row inside the excluded playlist is kept when the caller names it
 (`keepContentId`): a pin can point at another copy of the film in the playlist
 being viewed, and dropping that row would leave the preference pointing at
-nothing. The host therefore reads the pin BEFORE discovery.
+nothing. The host therefore reads the pin BEFORE discovery. When that pin is
+the route's *own* row, the kept copy and `currentSourceRow()` are the same
+stream, so `applyDiscoveredSources` drops the duplicate rather than listing it
+twice.
 
 ### Same title, different film
 
@@ -384,7 +387,9 @@ play.
 Whichever source ends up playing, the "playing" badge follows it: starting the
 route's own stream (Play, Resume, Restart, or the fallback after a pin does not
 apply) hands the badge back to the route row, or the picker and caption go on
-naming an alternative that is no longer running. And a source started through
+naming an alternative that is no longer running. That hand-back also
+invalidates a switch still resolving — the user chose the route stream, and an
+older resolution arriving afterwards would replace what they just asked for. And a source started through
 the picker or a pin is recorded in Recently Viewed exactly as an ordinary Play
 is — it is the same film, watched.