ERRATUM PW3-F1 (SYSTEMIC): the source_sha semantics

The law on this layer's face:
PW3 proved that source_sha across 164 layers seals _morphology_raw.txt regardless of what each layer read - boilerplate, not provenance. THE POLICY FROM THIS HOUR: every NEW layer seals the sha of what it actually read (W4-S1 v2 is the first); every SEALED layer keeps its bytes (the seal law) and this erratum travels with the build; the REPAIR-AND-INDEX allocation re-stamps them at the next deliberate re-seal, layer by layer, with true source lists. The old value remains meaningful as the CORPUS-ERA STAMP (the sighah-index generation) and is renamed so in re-stamped layers - never silently redefined.