diff --git a/bin/atlas-baker.js b/bin/atlas-baker.js
new file mode 100644
index 0000000..439fbf9
--- /dev/null
+++ b/bin/atlas-baker.js
@@ -0,0 +1,48 @@
+#!/usr/bin/env node
+// CLI entry. Parses args, dispatches to bake(), prints summary.
+
+const { bake } = require('../src/bake');
+
+function parseArgs(argv) {
+    const opts = {};
+    for (let i = 0; i < argv.length; i++) {
+        const a = argv[i];
+        const next = argv[i + 1];
+        switch (a) {
+            case '--in':            opts.inDir = next;   i++; break;
+            case '--out':           opts.outDir = next;  i++; break;
+            case '--atlas-id':      opts.atlasId = next; i++; break;
+            case '--tile-size':
+                opts.tileSize = (next === 'auto') ? 'auto' : parseInt(next, 10);
+                i++;
+                break;
+            case '--max-size':      opts.maxSize  = parseInt(next, 10); i++; break;
+            case '--lock':          opts.lockPath = next; i++; break;
+            case '--blocks-sight-pattern':
+                opts.blocksSightPattern = new RegExp(next); i++; break;
+            case '--verbose':       opts.verbose = true; break;
+            default:
+                console.error(`unknown arg: ${a}`);
+                process.exit(2);
+        }
+    }
+    return opts;
+}
+
+(async () => {
+    try {
+        const opts = parseArgs(process.argv.slice(2));
+        const result = await bake(opts);
+        console.log(
+            `OK ${result.atlasId}: ${result.tileCount} tiles, `
+            + `${result.boundsW}x${result.boundsH} px atlas`
+        );
+        process.exit(0);
+    } catch (err) {
+        console.error('ERROR:', err.message);
+        if (err.scanErrors) {
+            for (const e of err.scanErrors) console.error('  ', e);
+        }
+        process.exit(1);
+    }
+})();
diff --git a/src/bake.js b/src/bake.js
new file mode 100644
index 0000000..6bf6c97
--- /dev/null
+++ b/src/bake.js
@@ -0,0 +1,71 @@
+// src/bake.js
+const path = require('node:path');
+const { scanSourceDir } = require('./scan');
+const { loadLock, assignIds, serializeLock } = require('./lock');
+const { packMaxRects } = require('./pack');
+const { probeImageDims, composeAtlas, buildAtlasJson, writeOutputs } = require('./write');
+
+async function bake(opts) {
+    const {
+        inDir,
+        outDir,
+        atlasId,
+        tileSize = 64,
+        maxSize = 4096,
+        lockPath,
+        blocksSightPattern,
+    } = opts;
+
+    if (!atlasId) throw new Error('bake: --atlas-id is required');
+    if (!inDir)   throw new Error('bake: --in is required');
+    if (!outDir)  throw new Error('bake: --out is required');
+
+    const scanResult = scanSourceDir(inDir);
+    if (scanResult.errors.length > 0) {
+        const e = new Error(scanResult.errors[0]);
+        e.scanErrors = scanResult.errors;
+        throw e;
+    }
+
+    // Determine each source's tile-dimensions.
+    // - If --tile-size is a positive integer, all tiles are forced to that
+    //   size (composeAtlas auto-resizes mismatched sources via jimp).
+    // - If --tile-size === 'auto', each tile keeps its native dims.
+    for (const src of scanResult.sources) {
+        if (tileSize && tileSize !== 'auto') {
+            src.w = tileSize;
+            src.h = tileSize;
+        } else {
+            const dims = await probeImageDims(src.diffusePath);
+            src.w = dims.width;
+            src.h = dims.height;
+        }
+    }
+
+    const existingLock = loadLock(lockPath || path.join(outDir, 'tiles.atlas.lock.json'));
+    const { tiles, lock } = assignIds(scanResult.sources, existingLock, atlasId);
+
+    const packResult = packMaxRects(tiles, maxSize);
+    if (packResult.error) {
+        throw new Error(packResult.message);
+    }
+
+    const { diffuse, height } = await composeAtlas(packResult.placed, packResult.boundsW, packResult.boundsH);
+    const atlasJson = buildAtlasJson(
+        atlasId, 1, (tileSize === 'auto') ? null : tileSize,
+        packResult.boundsW, packResult.boundsH,
+        packResult.placed,
+        blocksSightPattern,
+    );
+
+    writeOutputs(outDir, diffuse, height, atlasJson, lock);
+    return {
+        outDir,
+        atlasId,
+        tileCount: packResult.placed.length,
+        boundsW: packResult.boundsW,
+        boundsH: packResult.boundsH,
+    };
+}
+
+module.exports = { bake };
diff --git a/tests/bake-deleted-tile.test.js b/tests/bake-deleted-tile.test.js
new file mode 100644
index 0000000..9886a72
--- /dev/null
+++ b/tests/bake-deleted-tile.test.js
@@ -0,0 +1,38 @@
+const { test } = require('node:test');
+const assert = require('node:assert');
+const path = require('node:path');
+const fs = require('node:fs');
+const os = require('node:os');
+const { bake } = require('../src/bake');
+
+test('bake-deleted: missing source moves ID to deleted[]', async () => {
+    const srcDir = fs.mkdtempSync(path.join(os.tmpdir(), 'atlas-src-'));
+    const outDir = fs.mkdtempSync(path.join(os.tmpdir(), 'atlas-out-'));
+    try {
+        // Copy only grass + stone from fixture (omit water)
+        const FIX = path.resolve(__dirname, 'fixtures/small-fresh');
+        fs.copyFileSync(path.join(FIX, 'grass_diffuse.png'), path.join(srcDir, 'grass_diffuse.png'));
+        fs.copyFileSync(path.join(FIX, 'stone_diffuse.png'), path.join(srcDir, 'stone_diffuse.png'));
+
+        // Pre-existing lock has all 3 names
+        fs.writeFileSync(
+            path.join(outDir, 'tiles.atlas.lock.json'),
+            JSON.stringify({
+                atlas_id: 'small_demo',
+                bindings: { grass: 1, stone: 2, water: 3 },
+                deleted: [],
+                next_id: 4,
+            }, null, 2),
+        );
+
+        await bake({ inDir: srcDir, outDir, atlasId: 'small_demo', tileSize: 32 });
+
+        const lock = JSON.parse(fs.readFileSync(path.join(outDir, 'tiles.atlas.lock.json'), 'utf8'));
+        assert.strictEqual(lock.bindings.water, undefined);
+        assert.deepStrictEqual(lock.deleted, [3]);
+        assert.strictEqual(lock.next_id, 4);  // not advanced
+    } finally {
+        fs.rmSync(srcDir, { recursive: true, force: true });
+        fs.rmSync(outDir, { recursive: true, force: true });
+    }
+});
diff --git a/tests/bake-determinism.test.js b/tests/bake-determinism.test.js
new file mode 100644
index 0000000..f9ff8ad
--- /dev/null
+++ b/tests/bake-determinism.test.js
@@ -0,0 +1,34 @@
+const { test } = require('node:test');
+const assert = require('node:assert');
+const path = require('node:path');
+const fs = require('node:fs');
+const os = require('node:os');
+const crypto = require('node:crypto');
+const { bake } = require('../src/bake');
+
+const FIX = path.resolve(__dirname, 'fixtures/small-fresh');
+
+function hashFile(p) {
+    return crypto.createHash('sha256').update(fs.readFileSync(p)).digest('hex');
+}
+
+test('bake-determinism: two fresh bakes produce identical outputs', async () => {
+    const out1 = fs.mkdtempSync(path.join(os.tmpdir(), 'atlas-det1-'));
+    const out2 = fs.mkdtempSync(path.join(os.tmpdir(), 'atlas-det2-'));
+    try {
+        await bake({ inDir: FIX, outDir: out1, atlasId: 'd', tileSize: 32 });
+        await bake({ inDir: FIX, outDir: out2, atlasId: 'd', tileSize: 32 });
+        const files = ['tiles.diffuse.atlas.png', 'tiles.height.atlas.png',
+                       'tiles.atlas.json',         'tiles.atlas.lock.json'];
+        for (const f of files) {
+            assert.strictEqual(
+                hashFile(path.join(out1, f)),
+                hashFile(path.join(out2, f)),
+                `${f} not bit-identical`,
+            );
+        }
+    } finally {
+        fs.rmSync(out1, { recursive: true, force: true });
+        fs.rmSync(out2, { recursive: true, force: true });
+    }
+});
diff --git a/tests/bake-fresh.test.js b/tests/bake-fresh.test.js
new file mode 100644
index 0000000..3de872c
--- /dev/null
+++ b/tests/bake-fresh.test.js
@@ -0,0 +1,43 @@
+const { test } = require('node:test');
+const assert = require('node:assert');
+const path = require('node:path');
+const fs = require('node:fs');
+const os = require('node:os');
+const { bake } = require('../src/bake');
+
+const FIX = path.resolve(__dirname, 'fixtures/small-fresh');
+
+test('bake-fresh: 3 sources, no lock, IDs 1..3', async () => {
+    const outDir = fs.mkdtempSync(path.join(os.tmpdir(), 'atlas-bake-fresh-'));
+    try {
+        const result = await bake({
+            inDir: FIX,
+            outDir,
+            atlasId: 'small_demo',
+            tileSize: 32,
+        });
+        assert.strictEqual(result.tileCount, 3);
+
+        const atlas = JSON.parse(fs.readFileSync(path.join(outDir, 'tiles.atlas.json'), 'utf8'));
+        assert.strictEqual(atlas.atlas_id, 'small_demo');
+        assert.strictEqual(atlas.tiles.length, 3);
+        // Alphabetical sort: grass < stone < water
+        assert.strictEqual(atlas.tiles[0].name, 'grass');
+        assert.strictEqual(atlas.tiles[0].id, 1);
+        assert.strictEqual(atlas.tiles[1].name, 'stone');
+        assert.strictEqual(atlas.tiles[1].id, 2);
+        assert.strictEqual(atlas.tiles[2].name, 'water');
+        assert.strictEqual(atlas.tiles[2].id, 3);
+
+        const lock = JSON.parse(fs.readFileSync(path.join(outDir, 'tiles.atlas.lock.json'), 'utf8'));
+        assert.strictEqual(lock.bindings.grass, 1);
+        assert.strictEqual(lock.bindings.water, 3);
+        assert.strictEqual(lock.next_id, 4);
+        assert.deepStrictEqual(lock.deleted, []);
+
+        assert.ok(fs.existsSync(path.join(outDir, 'tiles.diffuse.atlas.png')));
+        assert.ok(fs.existsSync(path.join(outDir, 'tiles.height.atlas.png')));
+    } finally {
+        fs.rmSync(outDir, { recursive: true, force: true });
+    }
+});
diff --git a/tests/bake-oversize-fail.test.js b/tests/bake-oversize-fail.test.js
new file mode 100644
index 0000000..58cabed
--- /dev/null
+++ b/tests/bake-oversize-fail.test.js
@@ -0,0 +1,32 @@
+const { test } = require('node:test');
+const assert = require('node:assert');
+const path = require('node:path');
+const fs = require('node:fs');
+const os = require('node:os');
+const { PNG } = require('pngjs');
+const { bake } = require('../src/bake');
+
+test('bake-oversize: tile that does not fit hard-fails', async () => {
+    const srcDir = fs.mkdtempSync(path.join(os.tmpdir(), 'atlas-over-src-'));
+    const outDir = fs.mkdtempSync(path.join(os.tmpdir(), 'atlas-over-out-'));
+    try {
+        // Single huge 256x256 tile, max canvas 128 -> cannot fit
+        const png = new PNG({ width: 256, height: 256 });
+        png.data.fill(255);
+        fs.writeFileSync(path.join(srcDir, 'huge_diffuse.png'), PNG.sync.write(png));
+
+        await assert.rejects(
+            () => bake({
+                inDir: srcDir,
+                outDir,
+                atlasId: 'over',
+                tileSize: 256,
+                maxSize: 128,
+            }),
+            /does not fit/,
+        );
+    } finally {
+        fs.rmSync(srcDir, { recursive: true, force: true });
+        fs.rmSync(outDir, { recursive: true, force: true });
+    }
+});
diff --git a/tests/bake-with-lock.test.js b/tests/bake-with-lock.test.js
new file mode 100644
index 0000000..4b1253b
--- /dev/null
+++ b/tests/bake-with-lock.test.js
@@ -0,0 +1,43 @@
+const { test } = require('node:test');
+const assert = require('node:assert');
+const path = require('node:path');
+const fs = require('node:fs');
+const os = require('node:os');
+const { bake } = require('../src/bake');
+
+const FIX = path.resolve(__dirname, 'fixtures/small-fresh');
+
+test('bake-with-lock: existing IDs preserved, new tile appended', async () => {
+    const outDir = fs.mkdtempSync(path.join(os.tmpdir(), 'atlas-bake-lock-'));
+    try {
+        // Pre-seed lock with grass=5, stone=6 (non-default IDs)
+        fs.writeFileSync(
+            path.join(outDir, 'tiles.atlas.lock.json'),
+            JSON.stringify({
+                atlas_id: 'small_demo',
+                bindings: { grass: 5, stone: 6 },
+                deleted: [],
+                next_id: 7,
+            }, null, 2),
+        );
+        const result = await bake({
+            inDir: FIX,
+            outDir,
+            atlasId: 'small_demo',
+            tileSize: 32,
+        });
+        assert.strictEqual(result.tileCount, 3);
+
+        const lock = JSON.parse(fs.readFileSync(path.join(outDir, 'tiles.atlas.lock.json'), 'utf8'));
+        assert.strictEqual(lock.bindings.grass, 5);   // preserved
+        assert.strictEqual(lock.bindings.stone, 6);   // preserved
+        assert.strictEqual(lock.bindings.water, 7);   // new
+        assert.strictEqual(lock.next_id, 8);
+
+        const atlas = JSON.parse(fs.readFileSync(path.join(outDir, 'tiles.atlas.json'), 'utf8'));
+        const ids = atlas.tiles.map(t => t.id).sort();
+        assert.deepStrictEqual(ids, [5, 6, 7]);
+    } finally {
+        fs.rmSync(outDir, { recursive: true, force: true });
+    }
+});