Exact guard, locations, and finite reversible encoding

Let $Q_{-}$, $Q_{+}$ denote the two regular transverse epochs and $Q_{0^{-}},Q_{0^{+}}$ their event germs. At the event, retained central edge slots have zero length and realize the same junction; they are metadata, not regular embedded one-cells.

The forward event rule has guard

It changes the mode to one, spends one permission, and chooses the outgoing germ without advancing $s$. A fixed abstract location map sends the incoming central slot and its endpoint labels to the outgoing event-junction slot; persistent labels are unchanged. No physical matter is transported through the patch by this metadata rule. If a spectator has an abstract location there, its location history is separately reserved.

Fix a finite parameter grid

stored exactly. Store rounded length reports only as reports. A rounded zero length cannot replace the exact guard: if $\ell =v(-s)$, floor quantization at resolution $\epsilon$ reports zero for $0\le -s<\epsilon /v$.

Let $x$ be a tuple of valid location words and $\tau (x)$ its fixed event transport. On valid forward codewords prescribe

At zero, both central reports are zero and all common noncentral formulas agree, so the report words remain valid.