feat: cue-phrase candidate extraction + testable extract.js (task/smarter-candidate-extraction)

Catch artist names written in lowercase right after a cue phrase ("check out devourment",
"by cattle decapitation", "fan of ...") — the Title-Case/ALL-CAPS pass missed those.

- extension/extract.js (new): pure extraction (matchesIn + new cueMatchesIn + allMatchesIn),
  UMD so it loads as a content script AND require()s in node for tests. The cue pass uses the
  regex `d` flag to map matches back to positions for in-place wrapping; a small cue-stoplist
  drops "the/this/new/..." right after the cue.
- extension/content.js: extraction now comes from globalThis.RSLExtract.allMatchesIn
  (Title-Case + cue union), keeping the existing position-based wrapping.
- extension/manifest.json: load extract.js before content.js.
- extension/extract.test.cjs (new) + scripts/check.sh: 6 node:test cases for the extraction
  logic; check.sh now runs the extension tests too (16 total, green).
- README: updated the detection limitation note.

Deferred (design item 2): merging names split across inline formatting (cross-node) — more
involved; left as a follow-up.

Verified: scripts/check.sh green (16 tests). In-browser behavior is logic-verified only (no
headless Firefox); additive to the pending background-fix re-test — the [rsl] logs distinguish
"candidates found" from "resolve failed".

Source: task/smarter-candidate-extraction (objective/linker-improvements).

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

extension/extract.js

@@ -0,0 +1,88 @@
+// Pure candidate extraction from comment text. Loaded as a content script (defines
+// globalThis.RSLExtract; runs before content.js per manifest order) AND require()-able in
+// node for unit tests (extract.test.cjs). No DOM access here — strings in, matches out.
+//
+// Each match is { name, index, length } so the content script can wrap it in place.
+(function (root, factory) {
+  const api = factory();
+  root.RSLExtract = api;
+  if (typeof module !== "undefined" && module.exports) module.exports = api; // node (cjs)
+})(typeof globalThis !== "undefined" ? globalThis : this, function () {
+  "use strict";
+
+  // A token is a Capitalized / ALL-CAPS word; a Title-Case candidate is 1-4 tokens with a
+  // few lowercase connectors allowed inside ("Signs of the Swarm").
+  const TOKEN = "[A-Z][A-Za-z0-9'’.&\\-]*";
+  const CAND_RE = new RegExp(`${TOKEN}(?:[ ]+(?:${TOKEN}|of|the|and|&|in|on|to|for|a|an)){0,3}`, "g");
+  const CONNECTORS = new Set(["of", "the", "and", "&", "in", "on", "to", "for", "a", "an"]);
+
+  // Cue phrases that often precede an artist name written in lowercase
+  // ("check out devourment", "by cattle decapitation"). Group 1 = the next 1-2 words;
+  // the `d` flag gives us the group's position so the match can be wrapped in place.
+  const CUE_RE = /\b(?:by|check ?out|listen(?: to)?|recommend(?:ed|ations?)?|fan of|into|loves?|playing)\s+([A-Za-z][A-Za-z0-9'’.&-]*(?:\s+[A-Za-z0-9][A-Za-z0-9'’.&-]*)?)/gid;
+
+  // Common capitalized words that are almost never the artist being recommended.
+  // Deliberately small: the resolver's exact-name match is the real filter.
+  const STOP = new Set([
+    "I", "A", "An", "The", "And", "But", "Or", "Nor", "So", "Yet", "For", "If", "As",
+    "At", "By", "In", "On", "To", "Of", "Up", "Off", "Out", "It", "He", "She", "We",
+    "They", "You", "Me", "Him", "Her", "Us", "Them", "My", "Your", "His", "Its", "Our",
+    "Their", "This", "That", "These", "Those", "Is", "Are", "Was", "Were", "Be", "Been",
+    "Am", "Do", "Does", "Did", "Has", "Have", "Had", "Will", "Would", "Can", "Could",
+    "Should", "Not", "No", "Yeah", "Ok", "Okay", "Lol", "Imo", "Imho", "Tbh", "Edit",
+    "Reddit", "Spotify", "Bandcamp", "Youtube", "Google", "Apple", "Album", "Albums",
+    "Band", "Bands", "Song", "Songs", "Track", "Tracks", "Ep", "Lp", "Cd", "Op", "Vol",
+  ]);
+
+  // Lowercase words unlikely to be the artist immediately after a cue phrase.
+  const CUE_STOP = new Set([
+    "the", "this", "that", "a", "an", "it", "them", "him", "her", "us", "new", "more",
+    "some", "any", "good", "best", "my", "your", "his", "their", "out", "to", "one", "all",
+  ]);
+
+  const TRAILING_PUNCT = /[.,;:!?’'")\]]+$/u;
+
+  function matchesIn(text) {
+    const out = [];
+    CAND_RE.lastIndex = 0;
+    let m;
+    while ((m = CAND_RE.exec(text))) {
+      let str = m[0].replace(TRAILING_PUNCT, "");
+      const parts = str.split(/\s+/);
+      while (parts.length && CONNECTORS.has(parts[parts.length - 1].toLowerCase())) parts.pop();
+      str = parts.join(" ");
+      if (!str) continue;
+      const single = parts.length === 1;
+      if (single && (STOP.has(str) || str.length < 2 || /^\d+$/.test(str))) continue;
+      out.push({ name: str, index: m.index, length: str.length }); // only trailing trimmed
+    }
+    return out;
+  }
+
+  function cueMatchesIn(text) {
+    const out = [];
+    CUE_RE.lastIndex = 0;
+    let m;
+    while ((m = CUE_RE.exec(text))) {
+      const gi = m.indices && m.indices[1];
+      if (!gi) continue;
+      const phrase = text.slice(gi[0], gi[1]).replace(TRAILING_PUNCT, "");
+      if (!phrase) continue;
+      const first = phrase.split(/\s+/)[0];
+      if (first.length < 2 || CUE_STOP.has(first.toLowerCase()) || /^\d+$/.test(first)) continue;
+      out.push({ name: first, index: gi[0], length: first.length });           // 1-word
+      if (phrase.length > first.length) out.push({ name: phrase, index: gi[0], length: phrase.length }); // 1-2 word
+    }
+    return out;
+  }
+
+  // Union of Title-Case + cue matches, sorted for the in-place wrapper
+  // (ascending index, longer match first so the wrapper's overlap guard prefers it).
+  function allMatchesIn(text) {
+    const all = matchesIn(text).concat(cueMatchesIn(text));
+    all.sort((a, b) => a.index - b.index || b.length - a.length);
+    return all;
+  }
+
+  return { matchesIn, cueMatchesIn, allMatchesIn };
+});