---
name: a-mutation-that-reds-every-arm-proves-only-damage
description: "A purposeful red must redden the ONE arm whose claim it falsifies, with the sibling arms asserted INTACT in the same script — reddening everything proves only that the cell notices damage."
metadata: 
  node_type: memory
  type: feedback
  originSessionId: b2ce30ce-4a9b-4d37-be9e-2469321a0e95
  modified: 2026-08-22T09:33:08.851Z
---

A purposeful red is only evidence about the arm it was aimed at. If the mutation reddens EVERY
arm of a multi-arm cell, all it has proven is that the cell notices damage — which no one doubted.
The strong form starves exactly the mechanism one arm claims, ASSERTS THE SIBLINGS STILL INTACT in
the same script, and shows the cell passing through the earlier arms before refusing at the aimed one.

Measured 2026-08-22 (todlando, W5/#211 commit 1, ruled by me at the gate). Two reds, and the second
is the one that carries the lane: `decide`'s PER-ENDPOINT rule tier was starved with an empty slice
while the same script asserted `NODE_TIER_INTACT=True`. The cell passed arm (b) on the node-scope
tier at line 278 and then failed arm (c) at line 305, exit 100. That ordering is the proof: arm (c)
is genuinely about tiers 1-3 and is NOT satisfiable by the node-scope rule arm (b) already exercised.
Had the mutation reddened both, effect (2) would have been indistinguishable from a second spelling
of effect (1) — the exact thing the lane existed to separate.

**Why:** a multi-arm cell's risk is not that it fails to notice breakage, it is that two arms assert
the SAME claim in different words and nobody can tell. A blunt mutation cannot detect that; a
selective one is a direct test of whether the arms are independent claims.

**How to apply:** aim every purposeful red at one arm, print the sibling-intact assertion beside the
match-count and the mutated body, and report WHICH ARM refused and which arms it passed through
first — never just "the cell went red". **His refinement, and it is the operative half: THE WORK IS
DONE BY ASSERTING THE UNMUTATED SIBLING IN THE SAME SCRIPT, not by the mutation.** `NODE_TIER_INTACT=True`
printed beside `MATCH_COUNT=1` is what turns "the cell redded" into "the cell redded for the reason I
aimed at" — without that line the author has to ARGUE the discrimination instead of SHOWING it, and
an argued discrimination is the one a gater has to take on trust. Kin: [[unapplied-mutation-green-reads-as-a-passing-guard]]
(the mutation must LAND), [[mutate-the-defect-not-the-trigger]] (it must remove the DEFENSE),
[[structural-exclusion-cannot-be-mutation-proved]] (the green side: a green arm may be excluded by
construction), [[two-arm-rig-confounds-the-valve-with-arm-order]].