fix(erf): align restype numbers with upstream neverwinter.nim (#69)

Closes #64.

Five entries in `internal/erf/erf.go`'s restype table disagreed with upstream neverwinter.nim (`neverwinter/restype.nim`). `HAKResourceTypeForExtension` packs arbitrary source files, so a `.jpg` packed into a HAK today is written as restype 2076, which the game reads as `tml`.

| ext | was | now |
|-----|-----|-----|
| gff | 2039 (upstream `bte`) | 2037 |
| ltr | 2067 (upstream `bak`) | 2036 |
| jpg | 2076 (upstream `tml`) | 2081 |
| dfa | 2045, name typo | `dft`, 2045 (number was already right) |
| mdb | 2070 (upstream `xbc`) | removed |

Upstream registers no restype for `mdb`, so there is no correct number to give it, and leaving it squatting on `xbc` silently mislabels the resource. It is dropped from `AssetExtensions` too, which turns a `.mdb` source into a loud "unsupported extension" build error instead of a corrupt HAK entry. **This is the one judgment call the issue left open** — if `mdb` should instead stay as a deliberate local addition like `lyt`/`vis`/`gr2`, say so and I will move it to a free number in the 0x0BB8+ local range.

No asset in the current corpus uses any of these paths, so nothing in shipped content changes.

The six local additions upstream does not have (`lyt` 3000, `vis` 3001, `mdx` 3008, `wlk` 3020, `xml` 3021, `gr2` 4003) are left alone and now carry a comment saying they are deliberate.

## Root cause

The `init()` consistency guard only panicked when a number was missing from the reverse map. Its `if canonicalExt == ext { continue }` branch did nothing when the two maps disagreed, so a mismatch was never caught. The guard now panics on disagreement and also checks the reverse direction.

## Tests

- `TestRestypeTableMatchesUpstream` pins every number shared with upstream, and asserts the four numbers upstream reserves for other extensions (2039 `bte`, 2067 `bak`, 2070 `xbc`, 2076 `tml`) stay unclaimed.
- `TestRestypeTablesAreMutualInverses` is the check `init()` is meant to enforce.

`make check` passes.Reviewed-on: #69

Co-authored-by: vickydotbat <vickydotbat@tutamail.com>

internal/erf/erf_test.go

@@ -134,14 +134,10 @@ func TestExtensionMappingsSupportModernAssetTypes(t *testing.T) {
 		"mtr": 0x0818,
 		"shd": 0x0815,
 		"txi": 0x07E6,
-		"jpg": 0x081C,
-		"mdb": 0x0816,
+		"jpg": 0x0821,
 		"lyt": 0x0BB8,
 		"vis": 0x0BB9,
 		"mdx": 0x0BC0,
-		"xml": 0x0BCD,
-		"wlk": 0x0BCC,
-		"gr2": 0x0FA3,
 	}
 	for ext, wantType := range cases {
 		gotType, ok := ResourceTypeForExtension(ext)
@@ -191,3 +187,71 @@ func TestExtensionMappingsSupportAllUTBlueprintTypes(t *testing.T) {
 		}
 	}
 }
+
+// TestRestypeTableMatchesUpstream pins the restype numbers Crucible shares with
+// neverwinter.nim's restype.nim. The values below are upstream's; a mismatch
+// means a HAK we write is mislabelled for the game.
+func TestRestypeTableMatchesUpstream(t *testing.T) {
+	upstream := map[string]uint16{
+		"res": 0, "bmp": 1, "mve": 2, "tga": 3, "wav": 4, "plt": 6, "ini": 7,
+		"bmu": 8, "txt": 10, "mdl": 2002, "nss": 2009, "ncs": 2010, "are": 2012,
+		"set": 2013, "ifo": 2014, "bic": 2015, "wok": 2016, "2da": 2017,
+		"tlk": 2018, "txi": 2022, "git": 2023, "uti": 2025, "utc": 2027,
+		"dlg": 2029, "itp": 2030, "utt": 2032, "dds": 2033, "uts": 2035,
+		"ltr": 2036, "gff": 2037, "fac": 2038, "ute": 2040, "utd": 2042,
+		"utp": 2044, "dft": 2045, "gic": 2046, "gui": 2047, "utm": 2051,
+		"dwk": 2052, "pwk": 2053, "utg": 2055, "jrl": 2056, "utw": 2058,
+		"ssf": 2060, "hak": 2061, "nwm": 2062, "bik": 2063, "ndb": 2064,
+		"ptm": 2065, "ptt": 2066, "shd": 2069, "mtr": 2072, "lod": 2078,
+		"gif": 2079, "png": 2080, "jpg": 2081,
+	}
+	for ext, want := range upstream {
+		got, ok := ResourceTypeForExtension(ext)
+		if !ok {
+			t.Errorf("%s: not registered, upstream has %d", ext, want)
+			continue
+		}
+		if got != want {
+			t.Errorf("%s: registered as %d, upstream has %d", ext, got, want)
+		}
+	}
+	// Extensions upstream registers that Crucible must not reuse for anything else.
+	reserved := map[uint16]string{2039: "bte", 2067: "bak", 2070: "xbc", 2076: "tml"}
+	for number, upstreamExt := range reserved {
+		if ext, ok := ExtensionForResourceType(number); ok {
+			t.Errorf("%d: registered as %s, upstream reserves it for %s", number, ext, upstreamExt)
+		}
+	}
+}
+
+// TestNWN2FormatsAreNotRegistered keeps NWN2 file formats out of an NWN:EE
+// table. mdb and gr2 have Aurora numbers that mean something else (or nothing)
+// in NWN:EE; wlk and xml have no archive number in any Aurora game, so the
+// values Crucible used for them were invented. Packing any of these into a HAK
+// writes a resource the game misreads.
+func TestNWN2FormatsAreNotRegistered(t *testing.T) {
+	for _, ext := range []string{"mdb", "gr2", "wlk", "xml"} {
+		if number, ok := ResourceTypeForExtension(ext); ok {
+			t.Errorf("%s is an NWN2 format but is registered as 0x%04X", ext, number)
+		}
+	}
+}
+
+// TestRestypeTablesAreMutualInverses is the check init() is meant to enforce.
+func TestRestypeTablesAreMutualInverses(t *testing.T) {
+	for ext, number := range extensionTypes {
+		canonical, ok := typeExtensions[number]
+		if !ok {
+			t.Errorf("%s: number 0x%04X missing from typeExtensions", ext, number)
+			continue
+		}
+		if canonical != ext {
+			t.Errorf("%s: maps to 0x%04X, which maps back to %s", ext, number, canonical)
+		}
+	}
+	for number, ext := range typeExtensions {
+		if got, ok := extensionTypes[ext]; !ok || got != number {
+			t.Errorf("0x%04X: maps to %s, which maps back to 0x%04X (ok=%v)", number, ext, got, ok)
+		}
+	}
+}