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Cross-Map Interference Regression Suite

Regression audit — instantiates Context-Keyed Representation Switching

A standing battery that, after any edit to one representation, re-exercises all the others to prove the change didn't corrupt a map you weren't touching or break clean re-entry.

When many representations share a substrate, editing one can silently break another through a shared helper, a common parameter, or a leaked assumption. Cross-Map Interference Regression Suite is the standing test battery that catches exactly that. It is triggered by a map update, and its assertion is pointed and specific: the maps you did not touch must not move, and switching away from a map and back must still restore it intact. Its defining focus is interference and re-entry breakage — not whether the right map gets selected, but whether changing one map quietly corrupted the coherence of the others or the fidelity of returning to them. It is the enforcement arm of the update policy: no edit lands unless the suite stays green.

Example

A trading platform maintains per-market rule maps — EU, US, and JP — governing tick sizes, halt logic, and settlement. An engineer edits the EU map to handle a new tick-size regime. Before it merges, the suite replays a fixed set of golden scenarios against the US and JP maps as well, asserting their outputs are unchanged to the last field, and it runs a switch-away-and-return cycle on each market to confirm re-entry still reconstructs each map exactly. The suite goes red: a helper the EU change touched is shared with JP, and a JP settlement scenario now drifts by a rounding step. The interference is caught at the desk, not in Tokyo at market open.

How it works

What distinguishes it from ordinary tests is that it is update-triggered and interference-oriented. Its golden fixtures are organized per context, and its core assertions are cross-map — the untouched maps produce identical outputs — plus switch-and-return cycles that verify re-entry integrity. It does not grade selection accuracy (whether the right map was chosen); it assumes the right map and asks whether that map is still correct and cleanly restorable after a neighboring edit. As the teeth behind the reconsolidation policy, it converts "please be careful when editing shared code" into a gate a change must pass.

Tuning parameters

  • Coverage — which contexts and code paths the suite exercises. Whatever it does not cover is where blind interference hides, so coverage gaps are the real risk surface.
  • Golden strictness — exact-match assertions versus tolerances. Strict catches subtle drift but is brittle to benign change; loose tolerances let real corruption slip under the bar.
  • Trigger scope — re-run all maps on every edit versus only the likely-affected ones. Broader is safer but slower; narrower is fast but can miss a surprising shared dependency.
  • Re-entry depth — how many switch-away/return cycles are run per map, and how deep the integrity check goes after each.

When it helps, and when it misleads

It is essential wherever maps share substrate and one edit can silently break another — it is the backstop that lets teams change one context's representation without holding their breath about the rest.

Its defining trap is that a green suite is only as safe as its coverage: if the suite never exercises the interference path, it passes and ships false confidence. The classic misuses are trimming the suite to make CI fast (removing exactly the slow cross-map cases that catch the worst bugs) and re-baselining the golden outputs to make a failing test pass — which bakes the regression in as the new "correct." The discipline is to treat any needed change to the goldens as a red flag to investigate rather than rubber-stamp, and to grow coverage from every interference that ever escaped.[1]

How it implements the components

  • cross_context_interference_probe — the cross-map assertions are the probe: they actively check that editing one map left the others' outputs unchanged.
  • re_entry_integrity_test — the switch-away-and-return cycles verify that leaving a context and coming back restores its map exactly.
  • map_update_and_reconsolidation_policy — it is the enforcement mechanism of that policy: an update may only reconsolidate if the suite stays green.

It does NOT measure selection or disambiguation errors — that is Context Confusion Matrix's job — and it does not itself provide the isolation it checks for, which comes from Context-Tagged Namespace Partition and Selective Parameter Freezing.

Notes

It proves absence-of-interference only over what it covers — it is a backstop for isolation, not a substitute for it. Weak isolation paired with a strong suite still ships bugs in the gaps between releases, because the suite verifies the paths it knows about, not the ones the edit actually took.

References

[1] Regression testing re-runs a fixed battery to confirm that a change did not break previously-working behavior. The failure particular to a shared substrate is silent cross-map interference; the discipline that keeps the suite honest is refusing to re-baseline a golden output without first understanding why it moved. ↩