The Labelled Resonant Source Supplies the Endpoint Nullhomotopy
Let q_7 denote the retained labelled source with s_b=1, i=7, and let
r_7 be its normalized odd exceptional target on Bl_(u,a^2). Entries
518--519 show
The positive value is not merely known to vanish in a fitted quotient. By construction of the labelled total complex,
in the endpoint complex. Thus the required positive-endpoint nullhomotopy is the restricted source label itself. At the negative endpoint the target restriction is already zero.
For the endpoint restriction map
the corresponding mapping-fiber representative has the canonical form
Its cone equation is
No new carrier generator or post hoc homotopy is introduced. This is exactly why the source label had to survive Entries 509--515: forgetting it retains the nonzero endpoint value while deleting its canonical nullhomotopy.
This establishes existence and typing of the relative lift. It does not yet establish that its mapping-fiber class is nonzero or unique. The next decisive calculation is the relative boundary matrix: compute whether this pair survives modulo global boundaries and whether the quadratic absolute bulk maps injectively to the endpoint complex.