feat: stewardship doctrine + zero-dep test infra (closes issue/linker-code-stewards-and-test-infra)

Stand up code stewards + testing for the linker, adapted to its JS/Node stack:
- service/lib.js: extract the resolver's pure logic (norm + exact-name match + link
  builders) so it is unit-testable without the server side effect; resolver.js imports it.
- service/lib.test.js: node:test coverage of the precision lever (7 tests).
- scripts/check.sh: zero-dep gate (node --check + JSON validation + node --test).
- AGENTS.md: repo doctrine — plain-repo push flow (NOT towl's PR pipeline), the three
  stewards (quality/design/security), the test gate, standing decisions (MV2 stays; no ML).

Source: issue/linker-code-stewards-and-test-infra (inbox human-feedback 2026-06-16 —
"should have a set of code stewards ... ensure a testing infra gets setup and maintained").

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

service/lib.js

@@ -0,0 +1,34 @@
+// Pure, side-effect-free helpers for the resolver. Kept separate from resolver.js
+// (which has the HTTP-server side effect) so they can be unit-tested with `node --test`
+// without starting a server. The artist-match precision lever lives here.
+
+export const norm = (s) => String(s).normalize("NFKC").trim().toLowerCase();
+
+export const bandcampSearch = (n) => `https://bandcamp.com/search?q=${encodeURIComponent(n)}&item_type=b`;
+export const spotifySearch = (n) => `https://open.spotify.com/search/${encodeURIComponent(n)}`;
+
+// The precision lever: return the result whose name matches the candidate
+// case-insensitively, else null. `minScore` (MusicBrainz) additionally requires a
+// confidence score. Tolerates null/garbage items.
+export function pickArtist(name, items, { minScore = null } = {}) {
+  const want = norm(name);
+  return (
+    (items ?? []).find(
+      (a) => a && norm(a.name) === want && (minScore == null || (a.score ?? 0) >= minScore),
+    ) ?? null
+  );
+}
+
+// Link object for a confirmed Spotify hit (direct artist url when present, else search).
+export const spotifyResult = (hit) => ({
+  name: hit.name,
+  spotify: hit.external_urls?.spotify ?? spotifySearch(hit.name),
+  bandcamp: bandcampSearch(hit.name),
+});
+
+// Link object for a confirmed MusicBrainz hit (search urls — MB gives no platform ids).
+export const searchResult = (hit) => ({
+  name: hit.name,
+  spotify: spotifySearch(hit.name),
+  bandcamp: bandcampSearch(hit.name),
+});

service/lib.test.js

@@ -0,0 +1,51 @@
+// Unit tests for the resolver's pure logic (run with `node --test`). Zero-dep.
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { norm, bandcampSearch, spotifySearch, pickArtist, spotifyResult, searchResult } from "./lib.js";
+
+test("norm lowercases, trims, NFKC-normalizes", () => {
+  assert.equal(norm("  Cerebral Bore "), "cerebral bore");
+  assert.equal(norm("DEVOURMENT"), "devourment");
+});
+
+test("pickArtist matches case-insensitively, rejects non-matches", () => {
+  const items = [{ name: "Cattle Decapitation" }, { name: "Cerebral Bore" }];
+  assert.equal(pickArtist("cerebral bore", items)?.name, "Cerebral Bore");
+  assert.equal(pickArtist("CATTLE DECAPITATION", items)?.name, "Cattle Decapitation");
+  assert.equal(pickArtist("Notarealband", items), null);
+});
+
+test("pickArtist enforces minScore when given (MusicBrainz path)", () => {
+  const items = [{ name: "Devourment", score: 100 }, { name: "Devourment", score: 50 }];
+  assert.equal(pickArtist("Devourment", items, { minScore: 90 })?.score, 100);
+  assert.equal(pickArtist("Devourment", [{ name: "Devourment", score: 50 }], { minScore: 90 }), null);
+});
+
+test("pickArtist tolerates empty / garbage input", () => {
+  assert.equal(pickArtist("x", null), null);
+  assert.equal(pickArtist("x", []), null);
+  assert.equal(pickArtist("x", [null, { name: "y" }]), null);
+});
+
+test("spotifyResult prefers the direct url, falls back to search", () => {
+  const direct = spotifyResult({
+    name: "Devourment",
+    external_urls: { spotify: "https://open.spotify.com/artist/abc" },
+  });
+  assert.equal(direct.spotify, "https://open.spotify.com/artist/abc");
+  assert.match(direct.bandcamp, /^https:\/\/bandcamp\.com\/search\?q=Devourment/);
+
+  const noUrl = spotifyResult({ name: "Devourment" });
+  assert.equal(noUrl.spotify, "https://open.spotify.com/search/Devourment");
+});
+
+test("searchResult builds spotify + bandcamp search urls", () => {
+  const r = searchResult({ name: "Cerebral Bore" });
+  assert.equal(r.spotify, "https://open.spotify.com/search/Cerebral%20Bore");
+  assert.equal(r.bandcamp, "https://bandcamp.com/search?q=Cerebral%20Bore&item_type=b");
+});
+
+test("link builders url-encode", () => {
+  assert.equal(spotifySearch("A B"), "https://open.spotify.com/search/A%20B");
+  assert.ok(bandcampSearch("A&B").includes("A%26B"));
+});

service/package.json

@@ -6,6 +6,7 @@
   "description": "Tiny resolver service: candidate names -> confirmed-artist links (Spotify/Bandcamp).",
   "engines": { "node": ">=18" },
   "scripts": {
-    "start": "node resolver.js"
+    "start": "node resolver.js",
+    "test": "node --test"
   }
 }

service/resolver.js

@@ -6,10 +6,11 @@
 //     DIRECT artist links;
 //   * without creds -> MusicBrainz validation + Spotify/Bandcamp SEARCH links (zero setup).
 // Either way a candidate only resolves when an artist's name matches it case-insensitively
-// (the precision lever that keeps random capitalized words from being linked).
+// (the precision lever). The pure matching/link logic lives in lib.js (unit-tested).
 
 import { createServer } from "node:http";
 import { readFileSync } from "node:fs";
+import { norm, pickArtist, spotifyResult, searchResult } from "./lib.js";
 
 // --- minimal .env loader (no dependency) ------------------------------------
 try {
@@ -27,10 +28,6 @@ const USE_SPOTIFY = Boolean(SPOTIFY_ID && SPOTIFY_SECRET);
 const UA = "reddit-spotify-linker/0.1 (https://git.yapplesauce.com/paul/linker)";
 const MAX_CANDIDATES = 100;
 
-const norm = (s) => String(s).normalize("NFKC").trim().toLowerCase();
-const bandcampSearch = (n) => `https://bandcamp.com/search?q=${encodeURIComponent(n)}&item_type=b`;
-const spotifySearch = (n) => `https://open.spotify.com/search/${encodeURIComponent(n)}`;
-
 const cache = new Map(); // norm(name) -> { spotify, bandcamp, name } | null  (negatives cached too)
 
 // --- Spotify (optional) -----------------------------------------------------
@@ -57,13 +54,8 @@ async function viaSpotify(name) {
   const r = await fetch(url, { headers: { authorization: `Bearer ${token}` } });
   if (!r.ok) throw new Error(`spotify search http ${r.status}`);
   const j = await r.json();
-  const hit = (j.artists?.items ?? []).find((a) => norm(a.name) === norm(name));
-  if (!hit) return null;
-  return {
-    name: hit.name,
-    spotify: hit.external_urls?.spotify ?? spotifySearch(hit.name),
-    bandcamp: bandcampSearch(hit.name),
-  };
+  const hit = pickArtist(name, j.artists?.items);
+  return hit ? spotifyResult(hit) : null;
 }
 
 // --- MusicBrainz (zero-cred fallback) ---------------------------------------
@@ -87,9 +79,8 @@ async function viaMusicBrainz(name) {
   const r = await fetch(url, { headers: { "user-agent": UA, accept: "application/json" } });
   if (!r.ok) throw new Error(`musicbrainz http ${r.status}`);
   const j = await r.json();
-  const hit = (j.artists ?? []).find((a) => norm(a.name) === norm(name) && (a.score ?? 0) >= 90);
-  if (!hit) return null;
-  return { name: hit.name, spotify: spotifySearch(hit.name), bandcamp: bandcampSearch(hit.name) };
+  const hit = pickArtist(name, j.artists, { minScore: 90 });
+  return hit ? searchResult(hit) : null;
 }
 
 // --- resolve one candidate (cached) -----------------------------------------