Make graph projection traceable and self-healing

[jimador]

Projecting propositions into graph relationships works, but the step is opaque and has no notion of
staleness: nothing records which proposition produced which edge, edges carry no authority, and when
a source proposition changes the downstream projection just sits there out of date.

Make projection observable and self-healing — every projected edge carries lineage back to its
source propositions and their authority tier, a stale-cascade invalidates dependent projections when
a source changes, and each projection reports a success / skip / fail outcome.

Use cases

• Trace any graph edge back to the propositions and sources that produced it.
• Automatically invalidate downstream edges when a source proposition is revised, instead of serving
  stale structure.
• Spot a projection that silently failed by reading its recorded outcome rather than guessing.