T4: Old Tam's tips in normal worlds, with a setting

docs/TUTORIAL_DESIGN.md

@@ -1,8 +1,24 @@
 # Tutorial world design
 
-Status: **T1 and T2 built**: the whole tutorial, on the Valley island
-(seed 1337), with Old Tam the hermit. T3 (its own island) and T4 (hints in
-real worlds) are proposals.
+Status: **T1, T2 and T4 built**: the whole tutorial, on the Valley island
+(seed 1337), with Old Tam the hermit, and his tips in normal worlds. T3
+(its own island) waits for the worldlets.
+
+*As built in T4:*
+- 16 tips in data/hints.json, in Old Tam's voice: soaked, cold, freezing,
+  hungry, a poor diet, food poisoning, food gone rotten, nightfall, the
+  wolves' howl, the red moon, a hard winter, snow, a storm, out of
+  breath, a first proper shelter, and back on your feet after dying.
+- The `Hints` autoload (scripts/core/hints.gd) checks your own survival
+  statuses, the weather, the clock and your bag, plus two events (a howl,
+  a death), so tips work the same online (the server mirrors statuses).
+  Each shows once per player (user://hints.json), in list order, 16 s
+  apart, never while you're dead, and not in the tutorial world or on a
+  server.
+- A card top right (scripts/ui/hint_card.gd) for 14 s; H puts it away.
+  Pause menu: **Old Tam's tips** on/off and **Show again**. On by default.
+- tests/test_hints.gd. Headless runs never start tips unless a test asks
+  (so the suites can't use up your real ones).
 
 *As built in T2:*
 - All five chapters, 22 steps (data/tutorial.json), in Old Tam's voice: