docs(specs): group 2 feedback as amendments, and lift out what was never specified

Following the Kiro workflow rather than continuing to write tasks.

**A workflow error, corrected.** Two task groups -- a counter-example
ledger, and per-repository evolutionary prompting so developers can commit
dismissals and evolve the harness -- were appended to contributor-scan's
tasks.md on 2026-09-09 without passing requirements or design. They are not
refinements of scan integration; they are a different feature, and writing
them as tasks skipped the two phases that decide whether a feature is
shaped right. They are lifted to .kiro/specs/finding-feedback-loop/, at
brief, unapproved.

That brief states the boundary the design turns on: an optimiser may evolve
the QUESTION (the judge and residual prompts, which are how we ask) and
never the FACTS (tables, rulesets, the declared policy file, which are what
we claim). The closed-loop leak measured on 2026-09-05 is why -- five of
eleven candidate shapes were taught by the holdout pairs they then
recovered, reporting a -0.059 holdout Youden as +0.059. It also states the
acceptance test for the model's role: revert the three matcher fixes and
see whether the grouping rediscovers the known causes.

**Three requirements amendments, drafted and unapproved**, at the end of
contributor-scan/requirements.md:

- Req 5 should state what a report may repeat. libpng emitted 198 findings
  and nothing in the spec forbade it. Task 2.11 fixed pattern noise; the
  model layer's own suspicion band is still 38 of vampi's 60, and it is the
  same epistemic class -- an enumerated candidate the graph could not
  decide and an LLM affirmed.
- A family that cannot decide a class must say so. c/memory scored zero
  true positives on 89k lines of C for a structural reason, and a silent
  scan reads as a clean bill of health. Worse than noise because it is
  quiet, and the one failure mode the rung ladder does not already guard.
- Req 4.1 is satisfied by a checkout that cannot demonstrate detection at
  all -- libpng's CVE is out of family and no version of it can be
  otherwise. It should require one that can.

And what group 2 confirmed rather than changed: Req 8's overfitting warning
stopped a rule being extended until one repository was clean and forced the
access-control work onto pairs nobody tuned against; Req 3.3's honesty
counters are what made a budget stopping free work visible at all; and Req
11.2's byte-identical gates held through all nine defect fixes, which says
from the other side that the corpus could not have caught any of them.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01T7XD7x5KonMdmGRkp63EQG

.kiro/specs/contributor-scan/requirements.md

@@ -194,3 +194,65 @@ tables and queries can be checked for regressions that pair scoring cannot see.
 3. The system shall treat an unexplained loss of a previously-entailed finding as a regression to be
    investigated, not a number to be accepted.
 4. The baseline shall record the engine version, because a CPG engine change moves every verdict it produces.
+
+---
+
+## Proposed amendments from group 2 (drafted 2026-09-09, NOT approved)
+
+Group 2 was specified as the phase that can reshape the rest, and it did. These are the changes it argues for
+at the requirements level rather than the task level. They are recorded here unapproved; the tasks already
+merged into group 2 implement what was within the approved requirements, and these are the parts that are not.
+
+### Amendment A — Req 5 should state what a report may repeat
+
+**Why.** libpng emitted 198 findings, 163 of them a static pattern asserting that `memcpy` and `strcpy` are
+*present* in a library that uses them correctly throughout. Req 5 says the output must be one a contributor
+can act on; it does not say anything about volume, so nothing in the spec was violated by a report no
+contributor would read.
+
+**Proposed criterion.** *The report shall be proportionate to the evidence behind a finding: a rule whose only
+evidence is a text match shall be summarised once it exceeds a stated number of sites, and a finding a
+proposer reasoned about shall keep its detail whatever its rung. Nothing shall be dropped from
+`findings.json`, which remains the record a baseline is compared against.*
+
+Implemented in task 2.11 for pattern matches. **Not implemented, and the reason this is an amendment rather
+than a closed task:** the same argument applies to the model layer's own suspicion band, which is 38 of vampi's
+60 findings — an enumerated candidate that the graph could not decide and an LLM affirmed. That is the same
+epistemic class as a pattern match with an opinion attached, and treating it as a reasoned claim is what
+leaves 51 sections on a 520-line application.
+
+### Amendment B — a family that cannot decide a class shall say so
+
+**Why.** `c/memory` produced zero true positives across an 89k-line C library and three distinct classes of
+false one. The reason is structural: it models string functions, and libpng overflows through arithmetic. A
+silent scan currently reads as a clean bill of health, and the stated goal is that an LLM will help a
+developer dive in — so it will fluently explain a silence it has no basis for.
+
+**Proposed criterion.** *Where a family's abstraction cannot decide a weakness class, the system shall state
+the limit in the report rather than be silent about it, and no scan shall present the absence of findings as
+evidence of absence.*
+
+This is worse than noise because it is quiet, and it is the one failure mode the rung ladder does not already
+guard against.
+
+### Amendment C — Req 4 should require a checkout that can produce a true positive
+
+**Why.** Req 4.1 asks for "at least one known-vulnerable repository checkout at a vulnerable commit", and
+libpng satisfies it while being incapable of demonstrating detection: its CVE is out of family, and no
+version of it can be otherwise, because the library never calls a sink any family models. The requirement is
+met and the intent is not.
+
+**Proposed criterion.** *At least one pinned checkout shall carry a known vulnerability that a family can
+decide in principle, so that a scan producing nothing is distinguishable from an engine that cannot see.*
+
+vampi satisfies this for Python. Nothing satisfies it for C, and 2.15 exists to find out whether anything can.
+
+### What group 2 confirmed rather than changed
+
+* **Req 8's overfitting warning earned its place twice.** It stopped a rule being extended until libpng was
+  clean (2.13), and it forced the access-control precision work to be measured on pairs nobody tuned against
+  (2.6), where the leak fell 42.9% → 0.0% with pair-correct unchanged.
+* **Req 3.3's honesty counters were the load-bearing part.** `regions_unjudged` is what made a budget that
+  stopped free work visible at all.
+* **Req 11.2's byte-identical gates held through every one of nine defect fixes** — which says the same thing
+  from the other side: the corpus could not have caught any of them.