absorb
Fold another proposition's evidence onto this one: grounding, provenance entries, and source ids, all appended and deduplicated. Bumps reinforceCount by one — treating the absorbed proposition as a single fresh confirmation, not + other.reinforceCount (which would double-count whatever it had already been reinforced by).
Idempotent: if other's grounding, provenance, and source ids are already all present here, this is a repeat of an already-applied absorption (e.g. a rerun after the other side of a two-step merge failed to save), so the reinforceCount bump is skipped.
Return
a copy of this proposition carrying the union of both propositions' evidence
Parameters
other
the proposition whose evidence is being folded into this one