feat(web): Core Refactor Phase A — extract sampling and cache modules; add adaptive TTL + eviction heuristics, Redis PoC, and metrics wiring. Tests added for TTL, eviction, exports, splash-adaptive, card index, and service worker. Docs+roadmap updated.

code/tests/test_preview_ttl_adaptive.py

@@ -0,0 +1,51 @@
+from code.web.services import preview_cache as pc
+
+
+def _force_interval_elapsed():
+    # Ensure adaptation interval guard passes
+    if pc._LAST_ADAPT_AT is not None:  # type: ignore[attr-defined]
+        pc._LAST_ADAPT_AT -= (pc._ADAPT_INTERVAL_S + 1)  # type: ignore[attr-defined]
+
+
+def test_ttl_adapts_down_and_up(capsys):
+    # Enable adaptation regardless of env
+    pc._ADAPTATION_ENABLED = True  # type: ignore[attr-defined]
+    pc.TTL_SECONDS = pc._TTL_BASE  # type: ignore[attr-defined]
+    pc._RECENT_HITS.clear()  # type: ignore[attr-defined]
+    pc._LAST_ADAPT_AT = None  # type: ignore[attr-defined]
+
+    # Low hit ratio pattern (~0.1)
+    for _ in range(72):
+        pc.record_request_hit(False)
+    for _ in range(8):
+        pc.record_request_hit(True)
+    pc.maybe_adapt_ttl()
+    out1 = capsys.readouterr().out
+    assert "theme_preview_ttl_adapt" in out1, "expected adaptation log for low hit ratio"
+    ttl_after_down = pc.TTL_SECONDS
+    assert ttl_after_down <= pc._TTL_BASE  # type: ignore[attr-defined]
+
+    # Force interval elapsed & high hit ratio pattern (~0.9)
+    _force_interval_elapsed()
+    pc._RECENT_HITS.clear()  # type: ignore[attr-defined]
+    for _ in range(72):
+        pc.record_request_hit(True)
+    for _ in range(8):
+        pc.record_request_hit(False)
+    pc.maybe_adapt_ttl()
+    out2 = capsys.readouterr().out
+    assert "theme_preview_ttl_adapt" in out2, "expected adaptation log for high hit ratio"
+    ttl_after_up = pc.TTL_SECONDS
+    assert ttl_after_up >= ttl_after_down
+    # Extract hit_ratio fields to assert directionality if logs present
+    ratios = []
+    for line in (out1 + out2).splitlines():
+        if 'theme_preview_ttl_adapt' in line:
+            import json
+            try:
+                obj = json.loads(line)
+                ratios.append(obj.get('hit_ratio'))
+            except Exception:
+                pass
+    if len(ratios) >= 2:
+        assert ratios[0] < ratios[-1], "expected second adaptation to have higher hit_ratio"