H5 follow-up: short-rest at full HP can still refresh slots

handleDnDShortRest early-returned when HPCurrent >= HPMax, which dates
from when short rest was HP-only. After H5 (1cd53eb) added the partial
slot refresh, that gate left casters who hadn't been hit unable to
recover slots between fights — the most common slot-attrition scenario.

Loosen the gate: short rest is allowed when HP can heal OR any spell
slot has used > 0. New helper casterHasUsedSlots gates the slot branch.
Martial behavior unchanged (still bails at full HP). Two new tests.

internal/plugin/dnd_rest.go

@@ -81,24 +81,27 @@ func (p *AdventurePlugin) handleDnDShortRest(ctx MessageContext) error {
 		return p.SendDM(ctx.Sender,
 			"You're out of short rest charges. Take a `!rest long` to restore them.")
 	}
-	if c.HPCurrent >= c.HPMax {
-		return p.SendDM(ctx.Sender, "You're already at full HP. Save the charge for when you need it.")
-	}
-
-	conMod := abilityModifier(c.CON)
-	healDie := 1 + rand.IntN(6) // 1d6
-	heal := healDie + conMod
-	if heal < 1 {
-		heal = 1
-	}
-	if c.Level >= 5 {
-		heal *= 2 // v1.0 §10.1: "x2 at levels 5+"
+	hpFull := c.HPCurrent >= c.HPMax
+	hasRefreshableSlots, _ := casterHasUsedSlots(ctx.Sender)
+	if hpFull && !hasRefreshableSlots {
+		return p.SendDM(ctx.Sender, "You're at full HP and your slots are full. Save the charge for when you need it.")
 	}
 
 	before := c.HPCurrent
-	c.HPCurrent += heal
-	if c.HPCurrent > c.HPMax {
-		c.HPCurrent = c.HPMax
+	if !hpFull {
+		conMod := abilityModifier(c.CON)
+		healDie := 1 + rand.IntN(6) // 1d6
+		heal := healDie + conMod
+		if heal < 1 {
+			heal = 1
+		}
+		if c.Level >= 5 {
+			heal *= 2 // v1.0 §10.1: "x2 at levels 5+"
+		}
+		c.HPCurrent += heal
+		if c.HPCurrent > c.HPMax {
+			c.HPCurrent = c.HPMax
+		}
 	}
 	c.ShortRestCharges--
 	now := time.Now().UTC()
@@ -112,9 +115,16 @@ func (p *AdventurePlugin) handleDnDShortRest(ctx MessageContext) error {
 		return p.SendDM(ctx.Sender, "Couldn't save rest state: "+err.Error())
 	}
 
-	msg := fmt.Sprintf(
-		"🛌 **Short rest.** You recover **%d HP** (%d→%d / %d).\n_Charges remaining: %d. You're resting — `!zone` and `!expedition` locked for 1 hour._",
-		c.HPCurrent-before, before, c.HPCurrent, c.HPMax, c.ShortRestCharges)
+	var msg string
+	if c.HPCurrent > before {
+		msg = fmt.Sprintf(
+			"🛌 **Short rest.** You recover **%d HP** (%d→%d / %d).\n_Charges remaining: %d. You're resting — `!zone` and `!expedition` locked for 1 hour._",
+			c.HPCurrent-before, before, c.HPCurrent, c.HPMax, c.ShortRestCharges)
+	} else {
+		msg = fmt.Sprintf(
+			"🛌 **Short rest.** You catch your breath — HP already full (%d/%d).\n_Charges remaining: %d. You're resting — `!zone` and `!expedition` locked for 1 hour._",
+			c.HPCurrent, c.HPMax, c.ShortRestCharges)
+	}
 	if slotLine := dndShortRestSlotLine(slotsRestored); slotLine != "" {
 		msg += "\n_" + slotLine + "_"
 	}

internal/plugin/dnd_rest_test.go

@@ -265,6 +265,65 @@ func TestShortRest_RefreshesPartialSlotsForMage(t *testing.T) {
 	}
 }
 
+// TestShortRest_FullHPCasterCanRefreshSlots covers the H5 follow-up: a
+// caster at full HP with spent slots must still be allowed to short rest
+// to recover them. Before the fix the HP-full guard short-circuited and
+// the slot refresh was unreachable.
+func TestShortRest_FullHPCasterCanRefreshSlots(t *testing.T) {
+	setupRestTestDB(t)
+	uid := id.UserID("@short_full_hp_mage:example")
+	c := makeRestTestMage(t, uid, 5)
+	c.HPCurrent = c.HPMax
+	if err := SaveDnDCharacter(c); err != nil {
+		t.Fatal(err)
+	}
+	pool := slotsForClassLevel(ClassMage, 5)
+	for lvl, total := range pool {
+		for i := 0; i < total; i++ {
+			consumeSpellSlot(uid, lvl)
+		}
+	}
+
+	p := &AdventurePlugin{}
+	if err := p.handleDnDShortRest(MessageContext{Sender: uid}); err != nil {
+		t.Fatal(err)
+	}
+	got, _ := LoadDnDCharacter(uid)
+	if got.HPCurrent != got.HPMax {
+		t.Errorf("HP changed despite full-HP entry: %d/%d", got.HPCurrent, got.HPMax)
+	}
+	if got.ShortRestCharges != c.ShortRestCharges-1 {
+		t.Errorf("charge not spent: %d → %d", c.ShortRestCharges, got.ShortRestCharges)
+	}
+	slots, _ := getSpellSlots(uid)
+	if used := slots[1][1]; used != 0 {
+		t.Errorf("L1 used after short rest = %d, want 0", used)
+	}
+}
+
+// TestShortRest_FullHPMartialBails confirms a non-caster at full HP is
+// still told to save the charge — the relaxed gate only opens for casters
+// who actually have refreshable slots.
+func TestShortRest_FullHPMartialBails(t *testing.T) {
+	setupRestTestDB(t)
+	uid := id.UserID("@short_full_hp_fighter:example")
+	makeRestTestChar(t, uid, 5)
+	c, _ := LoadDnDCharacter(uid)
+	c.HPCurrent = c.HPMax
+	if err := SaveDnDCharacter(c); err != nil {
+		t.Fatal(err)
+	}
+
+	p := &AdventurePlugin{}
+	if err := p.handleDnDShortRest(MessageContext{Sender: uid}); err != nil {
+		t.Fatal(err)
+	}
+	got, _ := LoadDnDCharacter(uid)
+	if got.ShortRestCharges != c.ShortRestCharges {
+		t.Errorf("charge spent on no-op short rest: %d → %d", c.ShortRestCharges, got.ShortRestCharges)
+	}
+}
+
 func TestDndShortRestSlotLine(t *testing.T) {
 	if got := dndShortRestSlotLine(nil); got != "" {
 		t.Errorf("nil → %q, want empty", got)

internal/plugin/dnd_spells.go

@@ -543,6 +543,18 @@ func refundSpellSlot(userID id.UserID, slotLevel int) error {
 	return err
 }
 
+// casterHasUsedSlots reports whether any spell slot for userID has used>0.
+// Used by the short-rest gate so casters at full HP can still rest to
+// recover slots (partialRefreshSpellSlots is otherwise unreachable for
+// them).
+func casterHasUsedSlots(userID id.UserID) (bool, error) {
+	var n int
+	err := db.Get().QueryRow(
+		`SELECT COUNT(*) FROM dnd_spell_slots WHERE user_id = ? AND used > 0`,
+		string(userID)).Scan(&n)
+	return n > 0, err
+}
+
 // refreshSpellSlots resets used=0 across all of a player's slots. Called
 // on long rest.
 func refreshSpellSlots(userID id.UserID) error {