Label merged changes in watch and accept unlinked branch work

watch described a project change with the raw branch, ending in a bare " / " for merged work whose change read has branch null. It now uses the original_branch fallback the other descriptions use.

An unlinked change may list no branch on its trail, which made the containment check compare its original branch against an empty name and reject it. ID, trail, and repository equality already prove containment, so the branch comparison applies only when the trail lists a branch.

Drop the stray handleLifecycleTurnStart lines above entireTrailContextInjection's comment, which restoring main's text brought back.