---
name: absence-of-the-wrong-is-not-presence-of-the-right
description: A lineage/shape check proving the bad base is gone does not prove the fix is there; each claim is satisfiable while the other fails, and neither leg detects the other's failure.
metadata:
  type: feedback
---

Verifying a respun head is TWO independent claims, and running one while inferring
the other is how a respin ships looking correct:

- **absence-of-the-wrong** — the discarded shape is not an ancestor
- **presence-of-the-right** — the fix's sha IS an ancestor, and its evidence is in the tree

Each is satisfiable while the other fails. A head can be clean of the thrown-away
lineage and still be MISSING the fix; a head can carry the fix and still be STACKED
on the shape that was discarded. Neither leg detects the other's failure mode.

Measured 2026-08-29, CONDUIT/#236 respin (v0.65.0 lane, spt-core). deployah's intake
added a leg proving `110d1751` (the discarded golden-green shape) was NOT an ancestor
of shaped head `0c17eb09` — his framing: "a respin built on the discarded shape would
have passed every other leg." I ran the complement at my own checkout rather than
inferring it: `git merge-base --is-ancestor 27a14c1c 0c17eb09` (true), the negative arm
again (false), and `git show <sha>:<path>` to confirm all four named cells were present
in the tree AT that sha — not present on my branch, present on the thing being shipped.
deployah ruled the distinction the durable part; both nailed BY NAME is the version
that holds.

**How to apply:** on any respin, rebase, cherry-pick, reassembly or hand-off, run both
arms explicitly and name them separately in the report. Do not let a green negative arm
stand in for the positive one. The positive arm needs the EVIDENCE too, not just the
commit: read the file list (or the test-fn names) out of the tree at the shipped sha —
a sha being an ancestor does not prove a later commit did not revert its content.

Companion at the same run: the comfortable wrong cause was **named on the board in
advance** (the stderr tear) precisely so nobody reaches for it when a red lands — the
countermeasure to [[a-prior-red-lends-the-next-one-an-unearned-cause]]. Pre-registration
also stood unchanged: a red at any of the four zero-denominator cells is
STRUCTURAL-until-shown-otherwise and routes RCA-first, with neither party asserting a
mechanism before the delta test.

See also [[parity-membership-level-goes-blind-on-shared-files]],
[[a-battery-is-silent-about-arms-no-cell-drives]],
[[assemble-onto-the-repair-tip-not-a-sibling]].