feat(bird_x): add noise words + last-chance retry with strongest token

Cherry-picked from PR #24 (el-analista). Adds trending/viral/plugin/skill/tool
noise words to _extract_core_subject, and a last-chance retry that falls back
to the longest non-noise token when 2-word retry also returns 0 results.

cache.py and render.py env overrides were already on main.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_bird_x.py

@@ -0,0 +1,57 @@
+"""Tests for bird_x module."""
+
+import sys
+import unittest
+from pathlib import Path
+from unittest import mock
+
+sys.path.insert(0, str(Path(__file__).parent.parent / "scripts"))
+
+from lib import bird_x
+
+
+class TestExtractCoreSubject(unittest.TestCase):
+    def test_strips_trending_noise(self):
+        result = bird_x._extract_core_subject("trendiest Claude Code skills")
+        self.assertNotIn("trendiest", result)
+        self.assertIn("claude", result.lower())
+
+    def test_strips_tool_noise(self):
+        result = bird_x._extract_core_subject("best AI tools for coding")
+        self.assertNotIn("tools", result)
+        self.assertNotIn("best", result)
+
+    def test_strips_skill_noise(self):
+        result = bird_x._extract_core_subject("top claude code skills")
+        self.assertNotIn("skills", result)
+        self.assertNotIn("top", result)
+
+
+class TestBirdSearchRetries(unittest.TestCase):
+    def test_last_chance_retry_uses_strongest_token(self):
+        """When shorter retry also returns 0, uses longest non-noise token."""
+        empty = {"items": []}
+        with mock.patch.object(bird_x, "_extract_core_subject", return_value="best codex skill plugin"), \
+             mock.patch.object(bird_x, "parse_bird_response", return_value=[]), \
+             mock.patch.object(bird_x, "_run_bird_search", return_value=empty) as run_mock:
+            bird_x.search_x("best codex skill plugin", "2026-01-01", "2026-01-31", depth="quick")
+
+        # Should try: original, shorter (2-word), last-chance (strongest token)
+        self.assertEqual(run_mock.call_count, 3)
+        queries = [call.args[0] for call in run_mock.call_args_list]
+        # Last call should use "codex" (longest non-noise word)
+        self.assertIn("codex", queries[2])
+
+    def test_no_retry_when_first_query_has_results(self):
+        """No retry when first query succeeds."""
+        result = {"items": [{"id": "1"}]}
+        with mock.patch.object(bird_x, "_extract_core_subject", return_value="nano banana"), \
+             mock.patch.object(bird_x, "parse_bird_response", return_value=[{"id": "1"}]), \
+             mock.patch.object(bird_x, "_run_bird_search", return_value=result) as run_mock:
+            bird_x.search_x("nano banana prompting", "2026-01-01", "2026-01-31")
+
+        self.assertEqual(run_mock.call_count, 1)
+
+
+if __name__ == "__main__":
+    unittest.main()