implements PLN-0082

discussion/index.ndjson

@@ -1,5 +1,5 @@
 {"type":"meta","next_id":{"DSC":39,"AGD":42,"DEC":38,"PLN":87,"LSN":53,"CLSN":1}}
-{"type":"discussion","id":"DSC-0038","status":"open","ticket":"studio-packer-rgba8888-asset-pipeline","title":"Studio and Packer RGBA8888 Asset Pipeline Alignment","created_at":"2026-05-23","updated_at":"2026-05-23","tags":["studio","packer","assets","glyph-bank","palette","rgba8888","runtime-alignment"],"agendas":[{"id":"AGD-0041","file":"AGD-0041-studio-packer-rgba8888-asset-pipeline.md","status":"accepted","created_at":"2026-05-23","updated_at":"2026-05-23"}],"decisions":[{"id":"DEC-0037","file":"DEC-0037-studio-packer-rgba8888-asset-pipeline.md","status":"accepted","created_at":"2026-05-23","updated_at":"2026-05-23","ref_agenda":"AGD-0041"}],"plans":[{"id":"PLN-0081","file":"PLN-0081-rgba8888-packer-and-studio-spec-propagation.md","status":"done","created_at":"2026-05-23","updated_at":"2026-05-23","ref_decisions":["DEC-0037"]},{"id":"PLN-0082","file":"PLN-0082-rgba8888-palette-model-and-argb-conversion.md","status":"review","created_at":"2026-05-23","updated_at":"2026-05-23","ref_decisions":["DEC-0037"]},{"id":"PLN-0083","file":"PLN-0083-rgba8888-glyph-payload-emission-and-sizes.md","status":"review","created_at":"2026-05-23","updated_at":"2026-05-23","ref_decisions":["DEC-0037"]},{"id":"PLN-0084","file":"PLN-0084-rgba8888-packer-projections-and-workspace-apis.md","status":"review","created_at":"2026-05-23","updated_at":"2026-05-23","ref_decisions":["DEC-0037"]},{"id":"PLN-0085","file":"PLN-0085-rgba8888-tests-fixtures-and-conformance.md","status":"review","created_at":"2026-05-23","updated_at":"2026-05-23","ref_decisions":["DEC-0037"]},{"id":"PLN-0086","file":"PLN-0086-rgba8888-final-integration-and-residue-removal.md","status":"review","created_at":"2026-05-23","updated_at":"2026-05-23","ref_decisions":["DEC-0037"]}],"lessons":[]}
+{"type":"discussion","id":"DSC-0038","status":"open","ticket":"studio-packer-rgba8888-asset-pipeline","title":"Studio and Packer RGBA8888 Asset Pipeline Alignment","created_at":"2026-05-23","updated_at":"2026-05-23","tags":["studio","packer","assets","glyph-bank","palette","rgba8888","runtime-alignment"],"agendas":[{"id":"AGD-0041","file":"AGD-0041-studio-packer-rgba8888-asset-pipeline.md","status":"accepted","created_at":"2026-05-23","updated_at":"2026-05-23"}],"decisions":[{"id":"DEC-0037","file":"DEC-0037-studio-packer-rgba8888-asset-pipeline.md","status":"accepted","created_at":"2026-05-23","updated_at":"2026-05-23","ref_agenda":"AGD-0041"}],"plans":[{"id":"PLN-0081","file":"PLN-0081-rgba8888-packer-and-studio-spec-propagation.md","status":"done","created_at":"2026-05-23","updated_at":"2026-05-23","ref_decisions":["DEC-0037"]},{"id":"PLN-0082","file":"PLN-0082-rgba8888-palette-model-and-argb-conversion.md","status":"done","created_at":"2026-05-23","updated_at":"2026-05-23","ref_decisions":["DEC-0037"]},{"id":"PLN-0083","file":"PLN-0083-rgba8888-glyph-payload-emission-and-sizes.md","status":"review","created_at":"2026-05-23","updated_at":"2026-05-23","ref_decisions":["DEC-0037"]},{"id":"PLN-0084","file":"PLN-0084-rgba8888-packer-projections-and-workspace-apis.md","status":"review","created_at":"2026-05-23","updated_at":"2026-05-23","ref_decisions":["DEC-0037"]},{"id":"PLN-0085","file":"PLN-0085-rgba8888-tests-fixtures-and-conformance.md","status":"review","created_at":"2026-05-23","updated_at":"2026-05-23","ref_decisions":["DEC-0037"]},{"id":"PLN-0086","file":"PLN-0086-rgba8888-final-integration-and-residue-removal.md","status":"review","created_at":"2026-05-23","updated_at":"2026-05-23","ref_decisions":["DEC-0037"]}],"lessons":[]}
 {"type":"discussion","id":"DSC-0037","status":"done","ticket":"pbs-autocomplete-parameter-names","title":"PBS autocomplete parameter names for stdlib and method calls","created_at":"2026-05-08","updated_at":"2026-05-14","tags":["compiler-pbs","studio","lsp","autocomplete","signature-help","stdlib"],"agendas":[],"decisions":[],"plans":[],"lessons":[{"id":"LSN-0052","file":"discussion/lessons/DSC-0037-pbs-autocomplete-parameter-names/LSN-0052-canonical-callable-parameter-names-through-pbs-editor-assistance.md","status":"done","created_at":"2026-05-14","updated_at":"2026-05-14"}]}
 {"type":"discussion","id":"DSC-0036","status":"open","ticket":"pbs-symbol-documentation-and-hover-markdown","title":"Modelo de documentacao de simbolos em PBS e consumo markdown no hover","created_at":"2026-05-08","updated_at":"2026-05-08","tags":["compiler","compiler-pbs","studio","lsp","vscode","editor","hover","documentation","markdown"],"agendas":[{"id":"AGD-0039","file":"AGD-0039-pbs-symbol-documentation-and-hover-markdown.md","status":"open","created_at":"2026-05-08","updated_at":"2026-05-08"}],"decisions":[],"plans":[],"lessons":[]}
 {"type":"discussion","id":"DSC-0035","status":"done","ticket":"pbs-lsp-editor-assistance-wave-1","title":"Wave 1 de assistencia editorial via LSP para PBS no VS Code","created_at":"2026-05-08","updated_at":"2026-05-08","tags":["studio","lsp","vscode","compiler","compiler-pbs","editor","completion","hover","signature-help"],"agendas":[],"decisions":[],"plans":[],"lessons":[{"id":"LSN-0051","file":"discussion/lessons/DSC-0035-pbs-lsp-editor-assistance-wave-1/LSN-0051-compiler-backed-editor-assistance-for-pbs.md","status":"done","created_at":"2026-05-08","updated_at":"2026-05-08"}]}

discussion/workflow/plans/PLN-0082-rgba8888-palette-model-and-argb-conversion.md

@@ -2,9 +2,9 @@
 id: PLN-0082
 ticket: studio-packer-rgba8888-asset-pipeline
 title: RGBA8888 Palette Model and ARGB Conversion
-status: review
+status: done
 created: 2026-05-23
-completed:
+completed: 2026-05-23
 ref_decisions:
   - DEC-0037
 tags:
@@ -124,12 +124,12 @@ diagnostic wording to remove `indices 1..15`.
 
 ## Acceptance Criteria
 
-- [ ] `PackerPaletteV1` exposes `rgba8888` and no RGB565 field.
+- [x] `PackerPaletteV1` exposes `rgba8888` and no RGB565 field.
-- [ ] `PackerGlyphBankWalker` stores canonical RGBA values.
+- [x] `PackerGlyphBankWalker` stores canonical RGBA values.
-- [ ] Magenta is not special.
+- [x] Magenta is not special.
-- [ ] Alpha zero and partial alpha are valid palette data.
+- [x] Alpha zero and partial alpha are valid palette data.
-- [ ] All 16 palette indices are usable.
+- [x] All 16 palette indices are usable.
-- [ ] Unit tests cover conversion and palette indexing semantics.
+- [x] Unit tests cover conversion and palette indexing semantics.
 
 ## Dependencies
 

prometeu-packer/prometeu-packer-v1/src/main/java/p/packer/models/PackerPaletteV1.java

@@ -1,6 +1,5 @@
 package p.packer.models;
 
 public record PackerPaletteV1(
-        int[] originalArgb8888,
+        int[] rgba8888) {
-        short[] convertedRgb565) {
 }

prometeu-packer/prometeu-packer-v1/src/main/java/p/packer/repositories/PackerAssetWalker.java

@@ -383,13 +383,10 @@ public class PackerAssetWalker {
             if (!indexNode.isInt() || !paletteNode.isObject()) {
                 continue;
             }
-            final int originalCount = paletteNode.path("originalArgb8888").isArray()
+            final int colorCount = paletteNode.path("rgba8888").isArray()
-                    ? paletteNode.path("originalArgb8888").size()
+                    ? paletteNode.path("rgba8888").size()
                     : 0;
-            final int convertedCount = paletteNode.path("convertedRgb565").isArray()
+            palettes.add(new DeclaredPalette(indexNode.intValue(), colorCount));
-                    ? paletteNode.path("convertedRgb565").size()
-                    : 0;
-            palettes.add(new DeclaredPalette(indexNode.intValue(), Math.min(originalCount, convertedCount)));
         }
         palettes.sort(java.util.Comparator.comparingInt(DeclaredPalette::index));
         return List.copyOf(palettes);

prometeu-packer/prometeu-packer-v1/src/main/java/p/packer/repositories/PackerGlyphBankWalker.java

@@ -11,8 +11,7 @@ import java.nio.file.Path;
 import java.util.*;
 
 public class PackerGlyphBankWalker extends PackerAbstractBankWalker<PackerGlyphBankRequirements> {
-    private static final int MAX_COLORS_PER_PALETTE = 15;
+    private static final int MAX_COLORS_PER_PALETTE = 16;
-    private static final int COLOR_KEY_RGB = 0x00FF00FF;
     private static final Set<String> SUPPORTED_MIME_TYPES = Set.of(
             "image/png"
     );
@@ -69,58 +68,37 @@ public class PackerGlyphBankWalker extends PackerAbstractBankWalker<PackerGlyphB
             ));
         }
 
-        final Map<Integer, Integer> paletteIndexByRgb = new LinkedHashMap<>();
+        final Map<Integer, Integer> paletteIndexByRgba = new LinkedHashMap<>();
         final byte[] paletteIndices = new byte[image.getWidth() * image.getHeight()];
-        boolean partialAlphaFound = false;
         boolean exceededPaletteLimit = false;
 
         int offset = 0;
         for (var y = 0; y < image.getHeight(); y++) {
             for (var x = 0; x < image.getWidth(); x++) {
                 final int argb = image.getRGB(x, y);
-                final int alpha = (argb >>> 24) & 0xFF;
+                final int rgba = argbToRgba(argb);
-                final int rgb = argb & 0x00FFFFFF;
 
-                if (alpha == 0 || rgb == COLOR_KEY_RGB) {
+                Integer paletteIndex = paletteIndexByRgba.get(rgba);
-                    paletteIndices[offset++] = 0;
-                    continue;
-                }
-
-                if (alpha < 0xFF) {
-                    partialAlphaFound = true;
-                }
-
-                Integer paletteIndex = paletteIndexByRgb.get(rgb);
                 if (paletteIndex == null) {
-                    if (paletteIndexByRgb.size() >= MAX_COLORS_PER_PALETTE) {
+                    if (paletteIndexByRgba.size() >= MAX_COLORS_PER_PALETTE) {
                         exceededPaletteLimit = true;
                         paletteIndices[offset++] = 0;
                         continue;
                     }
-                    paletteIndex = paletteIndexByRgb.size() + 1;
+                    paletteIndex = paletteIndexByRgba.size();
-                    paletteIndexByRgb.put(rgb, paletteIndex);
+                    paletteIndexByRgba.put(rgba, paletteIndex);
                 }
 
                 paletteIndices[offset++] = paletteIndex.byteValue();
             }
         }
 
-        if (partialAlphaFound) {
-            diagnostics.add(new PackerDiagnostic(
-                    PackerDiagnosticSeverity.WARNING,
-                    PackerDiagnosticCategory.HYGIENE,
-                    "Tile contains partial alpha; flattening to RGB and ignoring alpha channel",
-                    fileProbe.path(),
-                    false
-            ));
-        }
-
         if (exceededPaletteLimit) {
             diagnostics.add(new PackerDiagnostic(
                     PackerDiagnosticSeverity.ERROR,
                     PackerDiagnosticCategory.STRUCTURAL,
                     "Tile image exceeds color limit for " + fileProbe.path().getFileName()
-                            + ": expected at most " + MAX_COLORS_PER_PALETTE + " colors for indices 1..15",
+                            + ": expected at most " + MAX_COLORS_PER_PALETTE + " RGBA8888 colors",
                     fileProbe.path(),
                     true
             ));
@@ -131,7 +109,7 @@ public class PackerGlyphBankWalker extends PackerAbstractBankWalker<PackerGlyphB
         }
 
         final var tile = new PackerTileIndexedV1(image.getWidth(), image.getHeight(), paletteIndices);
-        final var palette = buildPalette(paletteIndexByRgb);
+        final var palette = buildPalette(paletteIndexByRgba);
         // Disabled for now: derived tile/palette JSON artifacts are not emitted during normal walks.
         // If we want filesystem-side debug artifacts again, uncomment the call below.
         // serializeProbeArtifacts(fileProbe, assetRoot, tile, palette, diagnostics);
@@ -150,7 +128,7 @@ public class PackerGlyphBankWalker extends PackerAbstractBankWalker<PackerGlyphB
         final Object width = tile.get("width");
         final Object height = tile.get("height");
         final Object indices = tile.get("paletteIndices");
-        final Object colors = palette.get("originalArgb8888");
+        final Object colors = palette.get("rgba8888");
         return width instanceof Number
                 && height instanceof Number
                 && indices instanceof List<?>
@@ -224,39 +202,27 @@ public class PackerGlyphBankWalker extends PackerAbstractBankWalker<PackerGlyphB
     }
 
     private Map<String, Object> toPalettePayload(final PackerPaletteV1 palette) {
-        final List<Integer> convertedRgb565 = new ArrayList<>(palette.convertedRgb565().length);
-        for (final short value : palette.convertedRgb565()) {
-            convertedRgb565.add(Short.toUnsignedInt(value));
-        }
-
         return Map.of(
-                "originalArgb8888", palette.originalArgb8888(),
+                "rgba8888", palette.rgba8888()
-                "convertedRgb565", convertedRgb565
         );
     }
 
-    private PackerPaletteV1 buildPalette(final Map<Integer, Integer> paletteIndexByRgb) {
+    private PackerPaletteV1 buildPalette(final Map<Integer, Integer> paletteIndexByRgba) {
-        final int[] originalArgb8888 = new int[paletteIndexByRgb.size()];
+        final int[] rgba8888 = new int[paletteIndexByRgba.size()];
-        final short[] convertedRgb565 = new short[paletteIndexByRgb.size()];
+        for (final var entry : paletteIndexByRgba.entrySet()) {
-        for (final var entry : paletteIndexByRgb.entrySet()) {
+            final int rgba = entry.getKey();
-            final int rgb = entry.getKey();
+            final int index = entry.getValue();
-            final int index = entry.getValue() - 1;
+            rgba8888[index] = rgba;
-            final int argb = 0xFF000000 | rgb;
-            originalArgb8888[index] = argb;
-            convertedRgb565[index] = convertToRgb565(argb);
         }
-        return new PackerPaletteV1(originalArgb8888, convertedRgb565);
+        return new PackerPaletteV1(rgba8888);
     }
 
-    private short convertToRgb565(final int argb) {
+    private int argbToRgba(final int argb) {
-        final int red = (argb >> 16) & 0xFF;
+        final int alpha = (argb >>> 24) & 0xFF;
-        final int green = (argb >> 8) & 0xFF;
+        final int red = (argb >>> 16) & 0xFF;
+        final int green = (argb >>> 8) & 0xFF;
         final int blue = argb & 0xFF;
-
+        return (red << 24) | (green << 16) | (blue << 8) | alpha;
-        final int r5 = (red >> 3) & 0x1F;
-        final int g6 = (green >> 2) & 0x3F;
-        final int b5 = (blue >> 3) & 0x1F;
-        return (short) ((r5 << 11) | (g6 << 5) | b5);
     }
 
     private java.awt.image.BufferedImage readImage(

prometeu-packer/prometeu-packer-v1/src/main/java/p/packer/services/FileSystemPackerWorkspaceService.java

@@ -1161,22 +1161,19 @@ public final class FileSystemPackerWorkspaceService implements PackerWorkspaceSe
             Object paletteMetadata,
             String artifactFile,
             Map<Integer, Integer> declaredPaletteIndexByRgb) {
-        final int[] originalArgb8888 = originalPaletteColors(paletteMetadata);
+        final int[] rgba8888 = paletteColors(paletteMetadata);
-        if (originalArgb8888.length == 0) {
+        if (rgba8888.length == 0) {
             throw new IllegalStateException("Selected tile artifact is missing palette metadata required for palette remapping: " + artifactFile);
         }
         final byte[] remapped = Arrays.copyOf(tile.paletteIndices(), tile.paletteIndices().length);
         for (int index = 0; index < remapped.length; index += 1) {
             final int paletteIndex = Byte.toUnsignedInt(remapped[index]);
-            if (paletteIndex == 0) {
+            if (paletteIndex >= rgba8888.length) {
-                continue;
-            }
-            if (paletteIndex > originalArgb8888.length) {
                 throw new IllegalStateException("Tile palette index exceeds discovered palette size for artifact: " + artifactFile);
             }
-            final int originalArgb = originalArgb8888[paletteIndex - 1];
+            final int rgba = rgba8888[paletteIndex];
-            final Integer materialIndex = declaredPaletteIndexByRgb.get(rgb24(originalArgb));
+            final Integer materialIndex = declaredPaletteIndexByRgb.get(rgba);
-            if (materialIndex == null || materialIndex < 1 || materialIndex > 15) {
+            if (materialIndex == null || materialIndex < 0 || materialIndex > 15) {
                 throw new IllegalStateException("Unable to resolve canonical palette index for artifact color in " + artifactFile);
             }
             remapped[index] = (byte) (materialIndex & 0x0F);
@@ -1189,29 +1186,29 @@ public final class FileSystemPackerWorkspaceService implements PackerWorkspaceSe
         if (!(palettesNode instanceof ArrayNode palettesArray) || palettesArray.isEmpty()) {
             throw new IllegalStateException("Glyph packing requires at least one declared pipeline palette.");
         }
-        final JsonNode paletteNode = palettesArray.get(0).path("palette").path("originalArgb8888");
+        final JsonNode paletteNode = palettesArray.get(0).path("palette").path("rgba8888");
         if (!paletteNode.isArray() || paletteNode.isEmpty()) {
-            throw new IllegalStateException("Glyph packing requires originalArgb8888 entries in the declared pipeline palette.");
+            throw new IllegalStateException("Glyph packing requires rgba8888 entries in the declared pipeline palette.");
         }
         final LinkedHashMap<Integer, Integer> mapping = new LinkedHashMap<>();
         for (int index = 0; index < paletteNode.size(); index += 1) {
             final JsonNode colorNode = paletteNode.get(index);
             if (!colorNode.canConvertToInt()) {
-                throw new IllegalStateException("Declared pipeline palette contains a non-integer originalArgb8888 entry.");
+                throw new IllegalStateException("Declared pipeline palette contains a non-integer rgba8888 entry.");
             }
-            mapping.put(rgb24(colorNode.intValue()), index + 1);
+            mapping.put(colorNode.intValue(), index);
         }
         return Map.copyOf(mapping);
     }
 
-    private int[] originalPaletteColors(Object paletteMetadata) {
+    private int[] paletteColors(Object paletteMetadata) {
         if (paletteMetadata instanceof PackerPaletteV1 palette) {
-            return palette.originalArgb8888();
+            return palette.rgba8888();
         }
         if (!(paletteMetadata instanceof Map<?, ?> map)) {
             return new int[0];
         }
-        final Object colors = map.get("originalArgb8888");
+        final Object colors = map.get("rgba8888");
         if (!(colors instanceof List<?> list)) {
             return new int[0];
         }
@@ -1226,10 +1223,6 @@ public final class FileSystemPackerWorkspaceService implements PackerWorkspaceSe
         return values;
     }
 
-    private int rgb24(int argb) {
-        return argb & 0x00FFFFFF;
-    }
-
     private PackedAsset packSceneBank(PackerRuntimeAsset runtimeAsset, PackerAssetDeclaration declaration) {
         final ScenePackRequest request = runtimeAsset.walkProjection().buildCandidateFiles().stream()
                 .map(file -> file.metadata().get("scenePackRequest"))

prometeu-packer/prometeu-packer-v1/src/main/java/p/packer/services/PackerReadMessageMapper.java

@@ -109,17 +109,12 @@ public final class PackerReadMessageMapper {
                     "paletteIndices", List.copyOf(paletteIndices));
         }
         if (value instanceof PackerPaletteV1 palette) {
-            final List<Integer> originalArgb8888 = new java.util.ArrayList<>(palette.originalArgb8888().length);
+            final List<Integer> rgba8888 = new java.util.ArrayList<>(palette.rgba8888().length);
-            for (int argb : palette.originalArgb8888()) {
+            for (int rgba : palette.rgba8888()) {
-                originalArgb8888.add(argb);
+                rgba8888.add(rgba);
-            }
-            final List<Integer> convertedRgb565 = new java.util.ArrayList<>(palette.convertedRgb565().length);
-            for (short rgb565 : palette.convertedRgb565()) {
-                convertedRgb565.add(Short.toUnsignedInt(rgb565));
             }
             return Map.of(
-                    "originalArgb8888", List.copyOf(originalArgb8888),
+                    "rgba8888", List.copyOf(rgba8888));
-                    "convertedRgb565", List.copyOf(convertedRgb565));
         }
         if (value instanceof Map<?, ?> nestedMap) {
             final java.util.LinkedHashMap<String, Object> normalized = new java.util.LinkedHashMap<>();

prometeu-packer/prometeu-packer-v1/src/test/java/p/packer/repositories/PackerGlyphBankWalkerTest.java

@@ -5,8 +5,10 @@ import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
 import p.packer.models.PackerAssetCacheEntry;
 import p.packer.models.PackerFileCacheEntry;
-import p.packer.models.PackerTileIndexedV1;
+import p.packer.models.PackerDiagnostic;
 import p.packer.models.PackerGlyphBankRequirements;
+import p.packer.models.PackerPaletteV1;
+import p.packer.models.PackerTileIndexedV1;
 
 import javax.imageio.ImageIO;
 import java.awt.image.BufferedImage;
@@ -42,7 +44,7 @@ final class PackerGlyphBankWalkerTest {
                         null,
                         Map.of(
                                 "tile", Map.of("width", 16, "height", 16),
-                                "palette", Map.of("originalArgb8888", List.of(0xFFFFFFFF))),
+                                "palette", Map.of("rgba8888", List.of(0xFFFFFFFF))),
                         List.of())));
 
         final var result = walker.walk(assetRoot, new PackerGlyphBankRequirements(16), Optional.of(priorCache));
@@ -52,6 +54,54 @@ final class PackerGlyphBankWalkerTest {
         assertTrue(tile.paletteIndices().length > 0);
     }
 
+    @Test
+    void preservesRgba8888PaletteDataAndUsesIndexZeroAsOrdinaryColor() throws Exception {
+        final Path assetRoot = Files.createDirectories(tempDir.resolve("rgba"));
+        final Path filePath = assetRoot.resolve("tile.png");
+        final BufferedImage image = new BufferedImage(16, 16, BufferedImage.TYPE_INT_ARGB);
+        image.setRGB(0, 0, 0x80FF0000);
+        image.setRGB(1, 0, 0x00000000);
+        image.setRGB(2, 0, 0xFFFF00FF);
+        for (int y = 0; y < 16; y++) {
+            for (int x = 3; x < 16; x++) {
+                image.setRGB(x, y, 0xFF00FF00);
+            }
+        }
+        ImageIO.write(image, "png", filePath.toFile());
+
+        final PackerGlyphBankWalker walker = new PackerGlyphBankWalker(MAPPER);
+        final var result = walker.walk(assetRoot, new PackerGlyphBankRequirements(16));
+
+        assertTrue(result.diagnostics().stream().noneMatch(diagnostic -> diagnostic.message().contains("partial alpha")));
+        final var metadata = result.probeResults().getFirst().metadata();
+        final PackerTileIndexedV1 tile = (PackerTileIndexedV1) metadata.get("tile");
+        final PackerPaletteV1 palette = (PackerPaletteV1) metadata.get("palette");
+
+        assertEquals(0, Byte.toUnsignedInt(tile.paletteIndices()[0]));
+        assertEquals(1, Byte.toUnsignedInt(tile.paletteIndices()[1]));
+        assertEquals(2, Byte.toUnsignedInt(tile.paletteIndices()[2]));
+        assertArrayEquals(new int[]{0xFF000080, 0x00000000, 0xFF00FFFF, 0x00FF00FF}, palette.rgba8888());
+    }
+
+    @Test
+    void acceptsSixteenRgbaColorsAndRejectsSeventeenth() throws Exception {
+        final Path validRoot = Files.createDirectories(tempDir.resolve("sixteen"));
+        writeColorCountTile(validRoot.resolve("tile.png"), 16);
+
+        final PackerGlyphBankWalker walker = new PackerGlyphBankWalker(MAPPER);
+        final var valid = walker.walk(validRoot, new PackerGlyphBankRequirements(16));
+
+        assertTrue(valid.diagnostics().stream().noneMatch(PackerDiagnostic::blocking));
+
+        final Path invalidRoot = Files.createDirectories(tempDir.resolve("seventeen"));
+        writeColorCountTile(invalidRoot.resolve("tile.png"), 17);
+        final var invalid = walker.walk(invalidRoot, new PackerGlyphBankRequirements(16));
+
+        assertTrue(invalid.probeResults().stream()
+                .flatMap(probeResult -> probeResult.diagnostics().stream())
+                .anyMatch(PackerDiagnostic::blocking));
+    }
+
     private void writeTile(Path path) throws Exception {
         final BufferedImage image = new BufferedImage(16, 16, BufferedImage.TYPE_INT_ARGB);
         for (int y = 0; y < 16; y++) {
@@ -61,4 +111,18 @@ final class PackerGlyphBankWalkerTest {
         }
         ImageIO.write(image, "png", path.toFile());
     }
+
+    private void writeColorCountTile(Path path, int colorCount) throws Exception {
+        final BufferedImage image = new BufferedImage(16, 16, BufferedImage.TYPE_INT_ARGB);
+        for (int y = 0; y < 16; y++) {
+            for (int x = 0; x < 16; x++) {
+                final int index = Math.min(colorCount - 1, y * 16 + x);
+                final int red = (index * 17) & 0xFF;
+                final int green = (index * 31) & 0xFF;
+                final int blue = (index * 47) & 0xFF;
+                image.setRGB(x, y, 0xFF000000 | (red << 16) | (green << 8) | blue);
+            }
+        }
+        ImageIO.write(image, "png", path.toFile());
+    }
 }