Cross-validate item appearance tables against the C reference

Instrumented the C game on modern-rogue with a DUMP mode (patch in
testdata/c_seedcompat.patch) that forces the RNG seed and prints the
per-seed item appearance tables — potion colors, scroll names, ring
stones, wand/staff materials — in the normal init order, before initscr
so no terminal is needed. Captured its output for four seeds as
testdata/item_tables.golden.

TestSeedCompatItemTables regenerates the same tables from the Go port
via New(Params{Seed, Wizard: true}) and checks they match the golden
byte for byte. They do, for all four seeds — proving the LCG and its
consumption order through the whole init sequence (init_probs →
init_player → init_names → init_colors → init_stones → init_materials,
including init_player's arrow rnd(8)+rnd(15)) agree with C exactly.

testdata/README.md documents how to regenerate the golden.

game/seedcompat_test.go

@@ -0,0 +1,98 @@
+package game
+
+import (
+	"fmt"
+	"os"
+	"strings"
+	"testing"
+)
+
+// dumpItemTables formats a game's per-seed item appearance tables in the
+// same layout the instrumented C reference prints: the potion colors,
+// scroll names, ring stones, and wand/staff materials, each generated by
+// consuming the RNG in a fixed order during New().
+func dumpItemTables(seed int32, g *RogueGame) string {
+	var b strings.Builder
+
+	fmt.Fprintf(&b, "SEED %d\n", seed)
+
+	fmt.Fprintln(&b, "POTIONS")
+
+	for _, c := range g.Items.PotColors {
+		fmt.Fprintln(&b, c)
+	}
+
+	fmt.Fprintln(&b, "SCROLLS")
+
+	for _, s := range g.Items.ScrNames {
+		fmt.Fprintln(&b, s)
+	}
+
+	fmt.Fprintln(&b, "RINGS")
+
+	for _, s := range g.Items.RingStones {
+		fmt.Fprintln(&b, s)
+	}
+
+	fmt.Fprintln(&b, "STICKS")
+
+	for i := range g.Items.WandType {
+		fmt.Fprintf(&b, "%s %s\n", g.Items.WandType[i], g.Items.WandMade[i])
+	}
+
+	return b.String()
+}
+
+// TestSeedCompatItemTables proves the port's seed-compatibility claim: for
+// the same seed, the Go game generates the exact per-seed item appearance
+// tables as the C reference on modern-rogue. That requires the LCG and its
+// consumption order through the whole init sequence (init_probs →
+// init_player → init_names → init_colors → init_stones → init_materials) to
+// match C byte for byte. The golden is captured from an instrumented build
+// of the C game (testdata/README.md).
+func TestSeedCompatItemTables(t *testing.T) {
+	golden, err := os.ReadFile("testdata/item_tables.golden")
+	if err != nil {
+		t.Fatalf("read golden: %v", err)
+	}
+
+	// These must match the seeds the golden was generated from
+	// (testdata/README.md).
+	seeds := []int32{1, 42, 12345, 99999}
+
+	var got strings.Builder
+
+	for _, seed := range seeds {
+		g := New(Params{Seed: seed, Wizard: true})
+		got.WriteString(dumpItemTables(seed, g))
+	}
+
+	if got.String() != string(golden) {
+		t.Errorf("Go item tables diverge from the C reference at %s",
+			firstDiff(string(golden), got.String()))
+	}
+}
+
+// firstDiff returns a description of the first line where want and got
+// differ, for a readable failure.
+func firstDiff(want, got string) string {
+	wl := strings.Split(want, "\n")
+	gl := strings.Split(got, "\n")
+
+	for i := 0; i < len(wl) || i < len(gl); i++ {
+		w, g := "", ""
+		if i < len(wl) {
+			w = wl[i]
+		}
+
+		if i < len(gl) {
+			g = gl[i]
+		}
+
+		if w != g {
+			return fmt.Sprintf("line %d: C=%q Go=%q", i+1, w, g)
+		}
+	}
+
+	return "no line difference (trailing content?)"
+}

game/testdata/README.md

@@ -0,0 +1,28 @@
+# Seed-compatibility golden
+
+`item_tables.golden` is the per-seed item appearance tables (potion colors,
+scroll names, ring stones, wand/staff materials) captured from the **C
+reference** on the `modern-rogue` branch, for the seeds in the `seeds` list in
+`TestSeedCompatItemTables`. That test regenerates the same tables
+from the Go port and checks they match byte for byte — proving the LCG and its
+consumption order through the whole init sequence (`init_probs` →
+`init_player` → `init_names` → `init_colors` → `init_stones` →
+`init_materials`) agree with C.
+
+## Regenerating the golden
+
+`c_seedcompat.patch` adds a `DUMP` mode to the C `main.c`: with `DUMP` set it
+forces the RNG seed from `SEED`, runs the item-table init in the normal order,
+prints the tables, and exits before `initscr` (so no terminal is needed).
+
+```sh
+# from a checkout of the C reference (modern-rogue branch):
+git archive modern-rogue | tar -x -C /tmp/rogue-c
+cd /tmp/rogue-c
+patch -p1 < .../game/testdata/c_seedcompat.patch
+./configure && make
+for s in 1 42 12345 99999; do DUMP=1 SEED=$s ./rogue; done \
+    > .../game/testdata/item_tables.golden
+```
+
+The seed list must match the `seeds` slice in `TestSeedCompatItemTables`.

game/testdata/c_seedcompat.patch

@@ -0,0 +1,37 @@
+--- a/main.c	2026-07-24 03:02:38
++++ b/main.c	2026-07-24 02:48:31
+@@ -63,6 +63,34 @@
+ #endif
+ 	dnum = lowtime + md_getpid();
+     seed = dnum;
++
++    /* SEEDCOMPAT: dump the per-game item appearance tables for a fixed
++     * seed and exit, without initscr. The init sequence and everything
++     * it consumes from rnd() mirror the normal startup (main.c), so the
++     * tables are exactly what a real game with SEED would show. */
++    if (getenv("DUMP") != NULL)
++    {
++	int di;
++	char *sv = getenv("SEED");
++	if (sv != NULL)
++	    seed = atoi(sv);
++	printf("SEED %d\n", seed);
++	init_probs();
++	init_player();
++	init_names();
++	init_colors();
++	init_stones();
++	init_materials();
++	printf("POTIONS\n");
++	for (di = 0; di < MAXPOTIONS; di++) printf("%s\n", p_colors[di]);
++	printf("SCROLLS\n");
++	for (di = 0; di < MAXSCROLLS; di++) printf("%s\n", s_names[di]);
++	printf("RINGS\n");
++	for (di = 0; di < MAXRINGS; di++) printf("%s\n", r_stones[di]);
++	printf("STICKS\n");
++	for (di = 0; di < MAXSTICKS; di++) printf("%s %s\n", ws_type[di], ws_made[di]);
++	exit(0);
++    }
+ 
+     open_score();
+ 

game/testdata/item_tables.golden

@@ -0,0 +1,260 @@
+SEED 1
+POTIONS
+tangerine
+white
+ecru
+gold
+amber
+violet
+vermilion
+pink
+aquamarine
+plaid
+clear
+orange
+cyan
+tan
+SCROLLS
+miwhon garsnanih
+xomimi roke eshwedshu
+potwexrol ipbjorod turs evsnelg
+bekornan oxyfatox
+iv wexpo wun
+ha sefnelgtue whon pay
+alari wedit
+zantmon umzonski umwhonjo yot
+bluoxun rokkho yottrol sta
+vomarg microgcomp iteulkshu mung
+jo urokeep yuskiun
+ox xozantaks klisstaevs ag
+ipnih bek
+shu ami erk
+nejti zim
+iprol mic ishoxyvom fagan
+reacreti oodrol
+bytsri solsa tabu fri
+RINGS
+agate
+zircon
+jade
+tiger eye
+onyx
+germanium
+lapis lazuli
+emerald
+taaffeite
+kryptonite
+garnet
+ruby
+turquoise
+pearl
+STICKS
+wand steel
+wand platinum
+staff redwood
+staff pine
+wand silicon
+staff spruce
+staff pecan
+wand bone
+staff maple
+wand zinc
+wand iron
+wand pewter
+wand electrum
+staff dogwood
+SEED 42
+POTIONS
+blue
+green
+grey
+amber
+violet
+gold
+pink
+tan
+purple
+yellow
+plaid
+magenta
+turquoise
+cyan
+SCROLLS
+bek itod oxytaod oxy
+tarhovzant cre sname oxroy
+plemik ganod hyd wergerkpot
+hyd sol um bekzok
+esh eep ganmung
+anera ishsa ingala mon
+alasniklech viv
+yunejorn garro con nej
+dotrolther gopum eltitrol trolmonsri
+nes alazum
+itegopmung ti
+ere haeta wergla
+nejerecre poipi iprea
+ha falechrhov
+monskiwex sabitla frido
+rhovmar sno
+mar bekurzant satbuzum
+somon sri
+RINGS
+carnelian
+onyx
+jade
+granite
+stibotantalite
+kryptonite
+lapis lazuli
+germanium
+garnet
+tiger eye
+opal
+topaz
+agate
+peridot
+STICKS
+staff birch
+staff ebony
+staff redwood
+wand gold
+wand copper
+wand aluminum
+wand titanium
+wand mercury
+staff cypress
+staff bamboo
+staff dogwood
+wand silicon
+staff zebrawood
+wand beryllium
+SEED 12345
+POTIONS
+purple
+black
+grey
+brown
+plaid
+violet
+vermilion
+ecru
+orange
+turquoise
+tan
+magenta
+silver
+gold
+SCROLLS
+readalf shuplu ivnin
+plelaiv solel skibyt monha
+xo wun
+wedyfri o ewhonxo favompay
+eep zantreanelg
+plu buxo
+un zontabdan
+bie snik
+ulkitzant bluri
+apporg ash posnevly dennepwex
+u urval rol
+arzepotsno snovly pay snoropay
+pottox erewed faoxro
+ther sun ulkipo mik
+argzebfri elgrekli tuenepzon sehturssef
+isheep blumur
+wedash yuzimsun
+plupofri ski rejo fa
+RINGS
+onyx
+tiger eye
+alexandrite
+turquoise
+pearl
+emerald
+germanium
+sapphire
+zircon
+ruby
+granite
+stibotantalite
+opal
+diamond
+STICKS
+wand silicon
+staff ironwood
+staff holly
+wand gold
+staff mahogany
+wand iron
+wand brass
+wand pewter
+staff hemlock
+staff cherry
+staff elm
+wand mercury
+staff banyan
+staff dogwood
+SEED 99999
+POTIONS
+aquamarine
+plaid
+gold
+black
+vermilion
+red
+cyan
+tan
+orange
+violet
+brown
+clear
+silver
+green
+SCROLLS
+zant jocompan vomervly
+mur shusat prok
+prokmurklis oxysriklis
+ingcre prokbu whonengarg kli
+kli bot
+rokcoswerg ipsolsan klisvlypay
+glen yot whontox
+lechme markho fazim
+dalfsunbie micjosef cre comp
+vlyfumi bjorzantbot werg
+po argfidcos klipones
+ashtemarg ycrezim dalfiv whon
+turs unmisa zimpo therdo
+miccompuni uni neswex sef
+odwexing elwergmur mung
+itcon rhov nejmic lech
+garturs engseh ganish
+oodta whonorgsno monabmik vomyeng
+RINGS
+obsidian
+moonstone
+jade
+carnelian
+tiger eye
+taaffeite
+turquoise
+stibotantalite
+agate
+ruby
+onyx
+topaz
+germanium
+granite
+STICKS
+wand titanium
+wand brass
+wand silicon
+staff zebrawood
+wand mercury
+staff dogwood
+wand pewter
+staff cinnibar
+staff kukui wood
+staff banyan
+wand magnesium
+wand gold
+staff maple
+wand nickel