Adopt house golangci-lint config; fix all approved-linter findings

.golangci.yml is the prompts-repo standard verbatim plus one approved
exception (paralleltest, sneak 2026-07-06). Roughly 1,500 findings
fixed:

- autofix sweep (wsl_v5/nlreturn/intrange/modernize formatting), with
  the misspell autofix REVERTED where it rewrote authentic C game text
  ("missle vanishes" stays, with nolint and a comment)
- error handling: errcheck sites get real handling — saveFile now
  closes explicitly and removes corrupt saves, scoreboard writes are
  documented best-effort, err113 sentinel errors (ErrSaveOutOfDate,
  ErrScreenTooSmall); panics allowed for unrecoverable states per
  MEMORY.md policy
- gosec: real fixes (ParseInt for SEED, 0600 scorefile) and justified
  per-line nolints for provably-bounded conversions (randomMonsterLetter
  helper collapses eight rnd(26)+'A' sites)
- API tidying from linters: pointer receivers on flag types
  (recvcheck), msg helpers renamed addmsgf/doaddf/Printwf/MvPrintwf
  (goprintffuncname), myExit()/findFloor(monst)/mkGameInput(t) drop
  always-constant params (unparam), gameEnd carries no status
- gocritic/staticcheck: if-else chains to switches, the pack.c
  inventory filter untangled into matchesFilter, main.go split so
  defers run before exit (exitAfterDefer, funlen)
- revive doc comments on all exported flag types/consts/methods

Remaining findings are confined to linters pending sneak's exception
decision (mnd, gochecknoglobals, cyclop, nestif, gocognit, exhaustive,
goconst, testpackage); TODO.md records the state. MEMORY.md added at
repo root as the project's agent working notes.

game/potions.go

@@ -39,21 +39,26 @@ func (g *RogueGame) quaff() {
 	if obj == nil {
 		return
 	}
+
 	if obj.Kind != KindPotion {
 		if !g.Options.Terse {
 			g.msg("yuk! Why would you want to drink that?")
 		} else {
 			g.msg("that's undrinkable")
 		}
+
 		return
 	}
+
 	if obj == p.CurWeapon {
 		p.CurWeapon = nil
 	}
 
 	// Calculate the effect it has on the poor guy.
 	trip := p.On(Hallucinating)
+
 	g.leavePack(obj, false, false)
+
 	switch obj.PotionKind() {
 	case PotionConfusion:
 		g.doPot(PotionConfusion, !trip)
@@ -72,6 +77,7 @@ func (g *RogueGame) quaff() {
 			p.Stats.MaxHP++
 			p.Stats.HP = p.Stats.MaxHP
 		}
+
 		g.sight(0)
 		g.msg("you begin to feel better")
 	case PotionGainStrength:
@@ -81,6 +87,7 @@ func (g *RogueGame) quaff() {
 	case PotionDetectMonsters:
 		p.Flags.Set(SenseMonsters)
 		g.Fuse(DTurnSee, 1, HuhDuration, After)
+
 		if !g.turnSee(false) {
 			g.msg("you have a %s feeling for a moment, then it passes",
 				g.chooseStr("normal", "strange"))
@@ -88,24 +95,30 @@ func (g *RogueGame) quaff() {
 	case PotionDetectMagic:
 		// Potion of magic detection.  Show the potions and scrolls
 		show := false
+
 		if len(g.Level.Objects) > 0 {
 			g.scr.Hw.Clear()
+
 			for _, tp := range g.Level.Objects {
 				if tp.isMagic() {
 					show = true
+
 					g.scr.Hw.MvAddCh(tp.Pos.Y, tp.Pos.X, Magic)
 					g.Items.Potions[PotionDetectMagic].Know = true
 				}
 			}
+
 			for _, mp := range g.Level.Monsters {
 				for _, tp := range mp.Pack {
 					if tp.isMagic() {
 						show = true
+
 						g.scr.Hw.MvAddCh(mp.Pos.Y, mp.Pos.X, Magic)
 					}
 				}
 			}
 		}
+
 		if show {
 			g.Items.Potions[PotionDetectMagic].Know = true
 			g.showWin("You sense the presence of magic on this level.--More--")
@@ -118,16 +131,21 @@ func (g *RogueGame) quaff() {
 			if p.On(SenseMonsters) {
 				g.turnSee(false)
 			}
+
 			g.StartDaemon(DVisuals, 0, Before)
 			g.SeenStairs = g.seenStairs()
 		}
+
 		g.doPot(PotionLSD, true)
 	case PotionSeeInvisible:
 		show := p.On(CanSeeInvisible)
+
 		g.doPot(PotionSeeInvisible, false)
+
 		if !show {
 			g.invisOn()
 		}
+
 		g.sight(0)
 	case PotionRaiseLevel:
 		g.Items.Potions[PotionRaiseLevel].Know = true
@@ -139,14 +157,17 @@ func (g *RogueGame) quaff() {
 			if p.Stats.HP > p.Stats.MaxHP+p.Stats.Lvl+1 {
 				p.Stats.MaxHP++
 			}
+
 			p.Stats.MaxHP++
 			p.Stats.HP = p.Stats.MaxHP
 		}
+
 		g.sight(0)
 		g.comeDown(0)
 		g.msg("you begin to feel much better")
 	case PotionHaste:
 		g.Items.Potions[PotionHaste].Know = true
+
 		g.After = false
 		if g.addHaste(true) {
 			g.msg("you feel yourself moving much faster")
@@ -155,24 +176,30 @@ func (g *RogueGame) quaff() {
 		if p.IsRing(Left, RingAddStrength) {
 			addStr(&p.Stats.Str, -p.CurRing[Left].Bonus)
 		}
+
 		if p.IsRing(Right, RingAddStrength) {
 			addStr(&p.Stats.Str, -p.CurRing[Right].Bonus)
 		}
+
 		if p.Stats.Str < p.MaxStats.Str {
 			p.Stats.Str = p.MaxStats.Str
 		}
+
 		if p.IsRing(Left, RingAddStrength) {
 			addStr(&p.Stats.Str, p.CurRing[Left].Bonus)
 		}
+
 		if p.IsRing(Right, RingAddStrength) {
 			addStr(&p.Stats.Str, p.CurRing[Right].Bonus)
 		}
+
 		g.msg("hey, this tastes great.  It make you feel warm all over")
 	case PotionBlindness:
 		g.doPot(PotionBlindness, true)
 	case PotionLevitation:
 		g.doPot(PotionLevitation, true)
 	}
+
 	g.status()
 	// Throw the item away
 	g.callIt(&g.Items.Potions[obj.Which])
@@ -192,6 +219,7 @@ func (g *RogueGame) doPot(kind PotionKind, knowit bool) {
 	if !g.Items.Potions[kind].Know {
 		g.Items.Potions[kind].Know = knowit
 	}
+
 	t := g.spread(pp.time)
 	if !g.Player.On(pp.flags) {
 		g.Player.Flags.Set(pp.flags)
@@ -200,11 +228,14 @@ func (g *RogueGame) doPot(kind PotionKind, knowit bool) {
 	} else {
 		g.Lengthen(pp.daemon, t)
 	}
+
 	high, straight := pp.high, pp.straight
+
 	if kind == PotionSeeInvisible {
 		s := fmt.Sprintf("this potion tastes like %s juice", g.Fruit)
 		high, straight = s, s
 	}
+
 	g.msg("%s", g.chooseStr(high, straight))
 }
 
@@ -218,6 +249,7 @@ func (o *Object) isMagic() bool {
 	case KindPotion, KindScroll, KindWand, KindRing, KindAmulet:
 		return true
 	}
+
 	return false
 }
 
@@ -225,6 +257,7 @@ func (o *Object) isMagic() bool {
 // invis_on).
 func (g *RogueGame) invisOn() {
 	g.Player.Flags.Set(CanSeeInvisible)
+
 	for _, mp := range g.Level.Monsters {
 		if mp.On(Invisible) && g.seeMonst(mp) && !g.Player.On(Hallucinating) {
 			g.mvaddch(mp.Pos.Y, mp.Pos.X, mp.Disguise)
@@ -236,8 +269,10 @@ func (g *RogueGame) invisOn() {
 // turn_see).
 func (g *RogueGame) turnSee(turnOff bool) bool {
 	addNew := false
+
 	for _, mp := range g.Level.Monsters {
 		g.move(mp.Pos.Y, mp.Pos.X)
+
 		canSee := g.seeMonst(mp)
 		if turnOff {
 			if !canSee {
@@ -247,22 +282,27 @@ func (g *RogueGame) turnSee(turnOff bool) bool {
 			if !canSee {
 				g.standout()
 			}
+
 			if !g.Player.On(Hallucinating) {
 				g.addch(mp.Type)
 			} else {
-				g.addch(byte(g.rnd(26) + 'A'))
+				g.addch(g.randomMonsterLetter())
 			}
+
 			if !canSee {
 				g.standend()
+
 				addNew = true
 			}
 		}
 	}
+
 	if turnOff {
 		g.Player.Flags.Clear(SenseMonsters)
 	} else {
 		g.Player.Flags.Set(SenseMonsters)
 	}
+
 	return addNew
 }
 
@@ -271,9 +311,11 @@ func (g *RogueGame) turnSee(turnOff bool) bool {
 func (g *RogueGame) seenStairs() bool {
 	st := g.Level.Stairs
 	g.move(st.Y, st.X)
+
 	if g.inch() == Stairs { // it's on the map
 		return true
 	}
+
 	if g.Player.Pos == st { // it's under him
 		return true
 	}
@@ -282,9 +324,11 @@ func (g *RogueGame) seenStairs() bool {
 		if g.seeMonst(tp) && tp.On(Awake) { // visible and awake:
 			return true // it must have moved there
 		}
+
 		if g.Player.On(SenseMonsters) && tp.OldCh == Stairs {
 			return true
 		}
 	}
+
 	return false
 }