A Standard Ultraviolet Continuum Can Hide Supercritical Accretion in GN-z11

The ultraviolet continuum from a high-redshift accreting black hole is routinely used to infer its mass. GN-z11 offers a sharp test of whether that inference is secure. A thin-disk fit to its continuum gives an Eddington mass of M E=1.12 times10 7,, an order of magnitude above the (/)=6.2 plus or minus0.3 inferred from broad N iv. We show that this apparent tension is not imposed by the ultraviolet slope alone. We derive a closed-form criterion comparing the radius where observed photons are produced with the radius where a supercritical flow departs from efficient solution. For GN-z11, the criterion places the supercritical transition inside the ultraviolet-emitting region. Composite disks retaining the outer solution confirm this numerically, requiring out=3.1 -- 4.4,, yr-1 and placing =(1.2 -- 1.8) times10 cubed, inside =(2.6 -- 2.9) times10 cubed,. Replacing the inner about10 cubed by a supercritical flow shifts the fitted slope by only Δ =+0.08 to +0.11, comparable to uncertainties from standard spectral modelling. Reversing the radial ordering requires the effective transition to move outward by a factor 1.7 -- 2.1. Within our composite models, the measured slope constrains black-hole mass only to around 10 6,, an order of magnitude below the continuum Eddington mass. Continuum Eddington masses should therefore be treated as model-dependent bounds that assume global thin-disk efficiency. The same hierarchy appears in three additional JWST sources under the disk-dominated interpretation, where separation masses are only 4 -- 6 % of continuum Eddington masses. This distinction can substantially weaken the seed-mass and early-growth demands inferred from ultraviolet continua at cosmic dawn for the first massive black holes.