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/monsters.go

@@ -21,14 +21,17 @@ func (g *RogueGame) randMonster(wander bool) byte {
 	if wander {
 		mons = &wandMons
 	}
+
 	for {
 		d := g.Depth + (g.rnd(10) - 6)
 		if d < 0 {
 			d = g.rnd(5)
 		}
+
 		if d > 25 {
 			d = g.rnd(5) + 21
 		}
+
 		if mons[d] != 0 {
 			return mons[d]
 		}
@@ -38,10 +41,8 @@ func (g *RogueGame) randMonster(wander bool) byte {
 // newMonster picks a new monster and adds it to the list (monsters.c
 // new_monster).
 func (g *RogueGame) newMonster(tp *Monster, typ byte, cp Coord) {
-	levAdd := g.Depth - AmuletLevel
-	if levAdd < 0 {
-		levAdd = 0
-	}
+	levAdd := max(g.Depth-AmuletLevel, 0)
+
 	attachMon(&g.Level.Monsters, tp)
 	tp.Type = typ
 	tp.Disguise = typ
@@ -58,15 +59,19 @@ func (g *RogueGame) newMonster(tp *Monster, typ byte, cp Coord) {
 	tp.Stats.Dmg = mp.Stats.Dmg
 	tp.Stats.Str = mp.Stats.Str
 	tp.Stats.Exp = mp.Stats.Exp + levAdd*10 + expAdd(tp)
+
 	tp.Flags = mp.Flags
 	if g.Depth > 29 {
 		tp.Flags.Set(Hasted)
 	}
+
 	tp.Turn = true
 	tp.Pack = nil
+
 	if g.Player.IsWearing(RingAggravateMonsters) {
 		g.runto(cp)
 	}
+
 	if typ == 'X' {
 		tp.Disguise = g.rndThing()
 	}
@@ -81,11 +86,13 @@ func expAdd(tp *Monster) int {
 	} else {
 		mod = tp.Stats.MaxHP / 6
 	}
+
 	if tp.Stats.Lvl > 9 {
 		mod *= 20
 	} else if tp.Stats.Lvl > 6 {
 		mod *= 4
 	}
+
 	return mod
 }
 
@@ -93,23 +100,29 @@ func expAdd(tp *Monster) int {
 // (monsters.c wanderer).
 func (g *RogueGame) wanderer() {
 	tp := &Monster{}
+
 	var cp Coord
 	for {
-		cp, _ = g.findFloor(nil, 0, true)
+		cp, _ = g.findFloor(true)
 		if g.roomin(cp) != g.Player.Room {
 			break
 		}
 	}
+
 	g.newMonster(tp, g.randMonster(true), cp)
+
 	if g.Player.On(SenseMonsters) {
 		g.standout()
+
 		if !g.Player.On(Hallucinating) {
 			g.addch(tp.Type)
 		} else {
-			g.addch(byte(g.rnd(26) + 'A'))
+			g.addch(g.randomMonsterLetter())
 		}
+
 		g.standend()
 	}
+
 	g.runto(tp.Pos)
 }
 
@@ -117,10 +130,12 @@ func (g *RogueGame) wanderer() {
 // (monsters.c wake_monster).
 func (g *RogueGame) wakeMonster(y, x int) *Monster {
 	p := &g.Player
+
 	tp := g.Level.MonsterAt(y, x)
 	if tp == nil {
 		panic("can't find monster in wake_monster")
 	}
+
 	ch := tp.Type
 	// Every time he sees a mean monster, it might start chasing him
 	if !tp.On(Awake) && g.rnd(3) != 0 && tp.On(Mean) && !tp.On(Held) &&
@@ -128,24 +143,30 @@ func (g *RogueGame) wakeMonster(y, x int) *Monster {
 		tp.Dest = &p.Pos
 		tp.Flags.Set(Awake)
 	}
+
 	if ch == 'M' && !p.On(Blind) && !p.On(Hallucinating) &&
 		!tp.On(Found) && !tp.On(Cancelled) && tp.On(Awake) {
 		rp := p.Room
 		if (rp != nil && !rp.Flags.Has(Dark)) ||
 			distance(y, x, p.Pos.Y, p.Pos.X) < LampDist {
 			tp.Flags.Set(Found)
+
 			if !g.save(VsMagic) {
 				if p.On(Confused) {
 					g.Lengthen(DUnconfuse, g.spread(HuhDuration))
 				} else {
 					g.Fuse(DUnconfuse, 0, g.spread(HuhDuration), After)
 				}
+
 				p.Flags.Set(Confused)
+
 				mname := g.setMname(tp)
-				g.addmsg("%s", mname)
+				g.addmsgf("%s", mname)
+
 				if mname != "it" {
-					g.addmsg("'")
+					g.addmsgf("'")
 				}
+
 				g.msg("s gaze has confused you")
 			}
 		}
@@ -153,12 +174,14 @@ func (g *RogueGame) wakeMonster(y, x int) *Monster {
 	// Let greedy ones guard gold
 	if tp.On(Greedy) && !tp.On(Awake) {
 		tp.Flags.Set(Awake)
+
 		if p.Room.GoldVal != 0 {
 			tp.Dest = &p.Room.Gold
 		} else {
 			tp.Dest = &p.Pos
 		}
 	}
+
 	return tp
 }
 
@@ -174,6 +197,7 @@ func (g *RogueGame) givePack(tp *Monster) {
 // save_throw).
 func (g *RogueGame) saveThrow(which int, st *Stats) bool {
 	need := 14 + which - st.Lvl/2
+
 	return g.roll(1, 20) >= need
 }
 
@@ -185,9 +209,17 @@ func (g *RogueGame) save(which int) bool {
 		if p.IsRing(Left, RingProtection) {
 			which -= p.CurRing[Left].Bonus
 		}
+
 		if p.IsRing(Right, RingProtection) {
 			which -= p.CurRing[Right].Bonus
 		}
 	}
+
 	return g.saveThrow(which, &p.Stats)
 }
+
+// randomMonsterLetter picks a random monster display letter, used by the
+// hallucination effects (the C rnd(26)+'A' idiom).
+func (g *RogueGame) randomMonsterLetter() byte {
+	return byte(g.rnd(26) + 'A') //nolint:gosec // G115: 'A'..'Z' fits a byte
+}