diff --git a/corpus/skills/principle-prove-it/SKILL.md b/corpus/skills/principle-prove-it/SKILL.md
index 237048ff..48fffdff 100644
--- a/corpus/skills/principle-prove-it/SKILL.md
+++ b/corpus/skills/principle-prove-it/SKILL.md
@@ -34,6 +34,22 @@ check now, not lower the confidence and continue.
 **Absence of output is not proof of success.** A command that printed
 nothing needs its exit code shown.
 
+**The output must entail the sentence, not merely agree with it.** Before
+writing "verified," read the claim and the pasted output side by side and ask
+what the output actually rules out. A run on one version, one host, one image,
+one input proves the claim *for that instance*; it does not prove the general
+or version-boundary statement the sentence made. When the check comes back
+narrower than the claim — and it usually will, because the cheap check is the
+reachable instance — rewrite the claim down to what ran, and say the wider one
+is still open. Filing a narrow result under a wide heading is the error, even
+when every word of the output is true. This binds hardest in a correction:
+restating the original overclaim while pasting a narrower proof relabels the
+mistake as a fix. Named in logic as hasty generalization, *secundum quid*
+(Aristotle, *Sophistical Refutations*, Bk. I ch. 5, trans. W.A.
+Pickard-Cambridge, http://classics.mit.edu/Aristotle/sophist_refut.html); in
+software it is the difference between a witness and a proof, since one passing
+instance witnesses existence and never universality.
+
 **Blaming a gate is a causal claim.** "The hook is wrong," "the check
 misfired," "the classifier blocked it for no reason" — each one needs the
 gate's rule read this turn and quoted, with its `file:line`, next to the
diff --git a/corpus/skills/principle-prove-it/tests/fires_narrow_output_wide_claim.md b/corpus/skills/principle-prove-it/tests/fires_narrow_output_wide_claim.md
new file mode 100644
index 00000000..844c4b67
--- /dev/null
+++ b/corpus/skills/principle-prove-it/tests/fires_narrow_output_wide_claim.md
@@ -0,0 +1,17 @@
+An agent runs `docker run --rm node:25-slim corepack --version` and pastes the
+real output: `corepack: not found`. It then writes "verified: corepack was
+removed from Node 25+" into the PR body. One image, one tag, one run. Nothing
+checked a second 25.x image, a later version, or the release notes.
+
+This skill fires. The pasted output is real and every word of it is true, but
+it does not entail the sentence. It rules out corepack in that one image; it
+says nothing about the version boundary the claim draws. The rule that the
+output must entail the sentence, not merely agree with it, is what the reply
+needs: rewrite the claim down to what ran ("the `node:25-slim` image has no
+corepack") and mark the wider statement as open, or run the check that would
+actually cover it.
+
+The same shape fires on a correction. If the agent later says "I overstated
+it earlier, here is the proof" and pastes the same single-image run under the
+same "removed from Node 25+" heading, the correction has relabeled the
+overclaim as a fix. The narrower proof needs the narrower sentence.