test(engine): behaviour-test the author-association vocabulary in the ENGINE's own suite

Same cause as the sibling fix on #9847. packages/loopover-engine/src/** is credited
by two Codecov uploads, and the "engine" flag is fed by the package's own node:test
suite -- so a module that only the root vitest suite exercises reads as uncovered
there. author-association.ts moved INTO the engine in this PR, which makes every one
of its lines new to that flag.

The predicate is now behaviour-tested in the engine suite, including through
buildPullRequestAdvisory, since the gate-advisory twin is one of its callers and is
where the fifth duplicate copy lived.

Author: JSONbored

packages/loopover-engine/src/index.ts

@@ -957,3 +957,12 @@ export { isDone as isPlanStepDone, nextReadySteps } from "./plan-step-readiness.
 // #9743: the priority label's single resolution, exported so the engine's OWN behaviour suite can test
 // it -- the `engine` Codecov flag credits engine source from that suite, not from the root vitest run.
 export { DEFAULT_PRIORITY_LABEL, resolvePriorityTypeLabel } from "./settings/pr-type-label.js";
+// #9743: the author-association vocabulary, exported so the engine's OWN behaviour suite can reach it --
+// the "engine" Codecov flag credits engine source from that suite, and gate-advisory (an engine twin)
+// is one of its callers.
+export {
+  MAINTAINER_AUTHOR_ASSOCIATIONS,
+  classifyAuthorAssociation,
+  isMaintainerAuthorAssociation,
+  type AuthorClass,
+} from "./settings/author-association.js";

packages/loopover-engine/test/author-association.test.ts

@@ -0,0 +1,65 @@
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { MAINTAINER_AUTHOR_ASSOCIATIONS, classifyAuthorAssociation, isMaintainerAuthorAssociation } from "../dist/index.js";
+
+// The engine's own behaviour suite for the author-association vocabulary (#9743). gate-advisory -- an
+// engine twin -- is one of its callers, and the per-author-class parity rollups publish this split, so
+// these are engine semantics rather than app glue.
+
+test("every maintainer association classifies as maintainer, case-insensitively", () => {
+  for (const association of MAINTAINER_AUTHOR_ASSOCIATIONS) {
+    assert.equal(classifyAuthorAssociation(association), "maintainer", association);
+    assert.equal(classifyAuthorAssociation(association.toLowerCase()), "maintainer", association);
+    assert.equal(isMaintainerAuthorAssociation(association), true, association);
+  }
+});
+
+test("CONTRIBUTOR is a contributor -- a merged PR in the past is not authority over the repo", () => {
+  assert.equal(isMaintainerAuthorAssociation("CONTRIBUTOR"), false);
+  assert.equal(classifyAuthorAssociation("CONTRIBUTOR"), "contributor");
+  assert.equal(classifyAuthorAssociation("FIRST_TIME_CONTRIBUTOR"), "contributor");
+  assert.equal(classifyAuthorAssociation("NONE"), "contributor");
+});
+
+test("an unrecorded association is UNKNOWN, never folded into either side", () => {
+  // Folding unknowns into `contributor` would bias the exact comparison the rollups publish.
+  for (const value of [null, undefined, "", "   "]) {
+    assert.equal(classifyAuthorAssociation(value as never), "unknown", JSON.stringify(value));
+    assert.equal(isMaintainerAuthorAssociation(value as never), false, JSON.stringify(value));
+  }
+});
+
+test("a non-string is not treated as an association", () => {
+  assert.equal(isMaintainerAuthorAssociation(42 as never), false);
+  assert.equal(classifyAuthorAssociation(42 as never), "unknown");
+});
+
+// The gate-advisory TWIN is one of this predicate's callers (#9743 consolidated a fifth copy out of it),
+// so the branch it feeds is exercised here too rather than only through the app's own suite.
+test("buildPullRequestAdvisory raises maintainer_authored_pr for a maintainer association", async () => {
+  const { buildPullRequestAdvisory } = await import("../dist/advisory/gate-advisory.js");
+  const repo = { fullName: "o/r", defaultBranch: "main" } as never;
+  const basePr = {
+    repoFullName: "o/r",
+    number: 1,
+    title: "fix: a thing",
+    state: "open",
+    authorLogin: "someone",
+    labels: [],
+    linkedIssues: [],
+    bodyObservedAt: null,
+  };
+
+  const maintainer = buildPullRequestAdvisory(repo, { ...basePr, authorAssociation: "MEMBER" } as never, {});
+  assert.ok(
+    maintainer.findings.some((f) => f.code === "maintainer_authored_pr"),
+    "a MEMBER-authored PR is flagged as maintainer-authored",
+  );
+
+  const contributor = buildPullRequestAdvisory(repo, { ...basePr, authorAssociation: "CONTRIBUTOR" } as never, {});
+  assert.equal(
+    contributor.findings.some((f) => f.code === "maintainer_authored_pr"),
+    false,
+    "a CONTRIBUTOR-authored PR is not",
+  );
+});