docs(contributor-scan): what the evidence says, and what it changes

Spec feedback after group 2, recorded in the brief where the goal is
stated rather than in a task where it would be lost.

The standing test is that the tool must find bugs or it is SAST noise, and
that most developers already have dataflow in CodeQL and Semgrep and never
use it. That settles what the differentiator is: not the engine, which
they already have, but the RUNG -- a claim the graph decided, reported
without configuration. Everything below model_entailed is on trial.

The scoreboard, kept honest: vampi finds 3 of 3 known vulnerabilities at
model_entailed, including a second BOLA the engine found before it was in
the recipe, with 2 false positives that are endpoints the OpenAPI spec
declares public. libpng produced 198 rows and zero valid ones, for a
structural reason rather than a tuning one -- the library never calls a
sink the c/memory family models.

Nine defects this session, each found by a measurement and none by review;
three were one bug class in three matchers, two were a capability present
but unreachable. The teachable finding is not any one of them, it is that
a corpus of function-level pairs cannot see any of them, and every one
appeared within minutes of pointing the tool at a real repository. The
gates stayed byte-identical through all nine, which says the same thing
from the other side.

Two priorities change. 2.11, the suspicion band, becomes the critical path
rather than cleanup: libpng's 163 "API is present" rows are exactly the
noise the quote is about, and no arbiter accuracy survives shipping them.
And a family that cannot decide its class has to say so, because a silent
C scan reading as a clean bill of health is worse than noise -- it is
quiet.

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

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

@@ -66,3 +66,50 @@ record is not scattered:
 - Five bugs in `model-grounded-detection` shared one shape — a taint-specific assumption applied to every
   family, each found by a measurement rather than a check. Any new family-specific path should be audited for
   siblings before it is measured, not after.
+
+## What the evidence says so far (appended 2026-09-09, after group 2)
+
+This is a research project whose findings get taught, so a negative result is a deliverable. But the standing
+test the work has to pass is blunter than that:
+
+> "it must find the bugs, otherwise it's SAST noise. most devs know codeql / semgrep have dataflow
+> capabilities but never use it"
+
+That sentence settles what the differentiator is, and it is **not the dataflow engine**. CodeQL and Semgrep
+already have one and developers do not turn it on. What they will not do is write queries, tune a ruleset, or
+read two hundred rows to find the one that matters. So the product is the **rung** -- a claim the graph
+decided, reported without configuration -- and everything below `model_entailed` is on trial.
+
+### The scoreboard, honestly
+
+| checkout | known in-scope | found | rung | false positives |
+|---|---|---|---|---|
+| vampi (python, 520 lines) | 3 | **3** | all `model_entailed` | 2, both endpoints the OpenAPI spec declares public |
+| libpng (c, 89k lines) | 0 (its CVE is out of family) | — | — | 30 over the session, now 1 |
+
+vampi is the result worth teaching: SQL injection across two modules, a broken object-level authorization,
+and a second BOLA **the engine found before it was in the recipe**. libpng is the result worth being honest
+about: 198 rows, zero of them valid, and the reason is structural rather than a tuning problem -- the library
+never calls a sink the `c/memory` family models.
+
+### What the session actually demonstrated
+
+Nine defects, each found by a measurement and none by review. Three of them were one bug class in three
+matchers (`resolve` in `resolveUrl`, `user` in `users`, `gets` in `fgets`); two were capability present but
+unreachable (the model layer itself, then `query_batch`); two were a paid budget stopping unpaid work and a
+question scoped to a function when the bug crosses modules.
+
+The teachable finding is not any one of them. It is that **a corpus of function-level pairs cannot see any of
+them**, and every one appeared within minutes of pointing the tool at a real repository. The gates stayed
+byte-identical through all nine fixes, which is the same statement from the other side.
+
+### What this changes about priorities
+
+* **2.11 (the suspicion band) is the critical path**, not a cleanup task. libpng produced 163 rows that
+  assert an API is present rather than misused. That is precisely the noise the quote above is about, and no
+  amount of arbiter accuracy survives shipping it.
+* **A family that cannot decide its class must say so** (2.16). A silent C scan must not read as a clean bill
+  of health; that is worse than noise because it is quiet.
+* **Negative results get recorded as measurements, not as failures.** `c/memory` scoring zero on libpng is a
+  finding about the abstraction, and the artifact says which abstraction would reach it (size arithmetic,
+  i.e. a constraint problem) rather than leaving it as a gap to be tuned at.