Improve WPM pathing paint editor

AGENTS.md

@@ -112,6 +112,7 @@ Three tiers, cheapest first. Put a test in the cheapest tier that can actually c
    - `e2e/harness/vscodeLauncher.js` pins `workbench.editorAssociations` in the temp profile. Without it a `.w3u`/`.w3a` passed on the command line opens in the *text* editor on a cold `--extensionDevelopmentPath` start, because the extension host has not registered its custom editors yet — and no webview is ever created.
 
 ### Editable binary formats
+- `.imp` remains intentionally read-only: it is World Editor import-manager bookkeeping, not a useful standalone editing target for normal Wurst workflows.
 - **.w3i is an editable custom editor** (`wurst.w3iEditor`, in `mapDataPreview.ts`) backed by `casc-ts` `parseW3i`/`serializeW3i`, which use a **parse-prefix + opaque-tail** model: only leading string/scalar fields are editable; players/forces/lists are preserved verbatim in `file.tail` (and parsed best-effort for display only). Every save passes a round-trip safety gate (`serializeValidatedW3i`). TRIGSTR-backed strings edit `war3map.wts`; inline strings edit the w3i bytes. The other map-data formats remain read-only under `wurst.mapDataPreview` (the old read-only `renderW3i`/`parseW3i` in that file are retained but no longer routed to).
 - When adding a new editable binary format, mirror this: a casc-ts parser+serializer with a byte-exact round-trip test, a `CustomEditorProvider` with dirty tracking, and a serialize→re-parse→compare safety gate before any write.
 

e2e/harness/makeFixtures.js

@@ -118,6 +118,7 @@ function buildWpm() {
     for (let y = 4; y < 8; y++) {
         for (let x = 4; x < 8; x++) data[y * width + x] = 0x02; // walkability blocked
     }
+    data[7 * width + 9] = 0xd0; // unfloatable + unamphibious + no-peon-harvest: picker must preserve every bit
     return serializeWpm({ version: 0, width, height, data, tail: Buffer.alloc(0) });
 }
 

e2e/specs/wpm-editor.spec.js

@@ -128,6 +128,47 @@ test('a drag paints a line of cells as one undo step', async ({ openWpm }) => {
     await expect.poll(() => host.isDirty).toBe(false);
 });
 
+test('the brush size expands one gesture into a square of cells', async ({ openWpm }) => {
+    const { page, host } = await openWpm();
+    await page.click('#btnZoomFit');
+    await page.click('[data-tool="paint"]');
+    await page.fill('#brushSize', '3');
+    await expect(page.locator('#brushSizeValue')).toHaveText('3 × 3');
+
+    const box = await page.locator('#viewport').boundingBox();
+    await page.mouse.click(box.x + box.width / 2, box.y + box.height / 2);
+
+    await expect.poll(() => host.editLabels.length).toBe(1);
+    const painted = Number(/Paint (\d+)/.exec(host.editLabels[0])[1]);
+    expect(painted).toBeGreaterThan(1);
+    expect(painted).toBeLessThanOrEqual(9);
+});
+
+test('line and fill tools produce one undoable edit each', async ({ openWpm }) => {
+    const { page, host } = await openWpm();
+    await page.click('#btnZoomFit');
+    const box = await page.locator('#viewport').boundingBox();
+
+    await page.click('[data-tool="line"]');
+    const y = box.y + box.height / 2;
+    await page.mouse.move(box.x + box.width * 0.3, y);
+    await page.mouse.down();
+    await page.mouse.move(box.x + box.width * 0.7, y, { steps: 4 });
+    await page.mouse.up();
+    await expect.poll(() => host.editLabels.length).toBe(1);
+    expect(host.editLabels[0]).toMatch(/^Paint \d+ pathing cells$/);
+
+    await page.click('[data-tool="fill"]');
+    await page.mouse.click(box.x + box.width * 0.8, box.y + box.height * 0.8);
+    await expect.poll(() => host.editLabels.length).toBe(2);
+    expect(host.editLabels[1]).toMatch(/^Paint \d+ pathing cells$/);
+
+    host.undo();
+    await expect.poll(() => host.editLabels.length).toBe(2);
+    host.undo();
+    await expect.poll(() => host.isDirty).toBe(false);
+});
+
 test('the erase tool clears flags instead of painting them', async ({ openWpm }) => {
     const { page, host } = await openWpm();
     await page.click('#btnZoomFit');
@@ -171,6 +212,23 @@ test('Alt+click picks up the brush flags from the cell under the cursor', async
     await expect(page.locator('[data-tool="paint"]')).toHaveClass(/active/);
 });
 
+test('Alt-click samples the complete flag byte from a cell', async ({ openWpm }) => {
+    const { page } = await openWpm();
+    await page.click('#btnZoomFit');
+
+    const box = await page.locator('#viewport').boundingBox();
+    const cellSize = await page.locator('#wpmCanvas').evaluate((canvas) => Math.min(canvas.width / 16, canvas.height / 16));
+    await page.keyboard.down('Alt');
+    await page.mouse.click(box.x + box.width / 2 + cellSize, box.y + box.height / 2);
+    await page.keyboard.up('Alt');
+
+    await expect(page.locator('#brushValue')).toHaveText('0xD0');
+    await expect(page.locator('[data-brush-bit="16"]')).toBeChecked();
+    await expect(page.locator('[data-brush-bit="64"]')).toBeChecked();
+    await expect(page.locator('[data-brush-bit="128"]')).toBeChecked();
+    await expect(page.locator('[data-tool="paint"]')).toHaveClass(/active/);
+});
+
 test('saving writes bytes that re-parse to the painted map', async ({ openWpm }) => {
     const { page, host } = await openWpm();
     await page.click('#btnZoomFit');

scripts/test-webview.js

@@ -1088,6 +1088,8 @@ function testWpmEditorInlineScriptAndRecoveryGuards() {
         .replace('${wpm.width}', '4')
         .replace('${wpm.height}', '4')
         .replace('${dataBase64}', 'AAAAAAAAAAAAAAAAAAAAAA==')
+        .replace('${JSON.stringify(colorTable)}', '[[0, 0, 0]]')
+        .replace('${JSON.stringify(WPM_FLAG_DEFS.map(({ bit, label }) => ({ bit, label })))}', '[]')
         .replace(/\\`/g, '`')
         .replace(/\\\$\{/g, '${');
     // eslint-disable-next-line sonarjs/constructor-for-side-effects -- parsing the real inline script is the assertion.
@@ -1097,6 +1099,21 @@ function testWpmEditorInlineScriptAndRecoveryGuards() {
     assert.ok(!host.includes('doc.editDepth'), 'WPM dirty tracking must not use branch-unsafe edit depth');
 }
 
+function testWpmFlagSemantics() {
+    const { WPM_FLAG_DEFS, WPM_KNOWN_VERSION, wpmCellRgb, wpmFlagLabels } = loadTsModuleWithMocks('src/features/wpmPreview.ts', {
+        vscode: {},
+        'casc-ts/formats': {},
+        './diagnostics': {},
+        './webviewShared': {},
+        './webviewUtils': {},
+    });
+    assert.strictEqual(WPM_KNOWN_VERSION, 0);
+    assert.deepStrictEqual(WPM_FLAG_DEFS.map((definition) => definition.bit), [1, 2, 4, 8, 16, 32, 64, 128]);
+    assert.deepStrictEqual(wpmFlagLabels(0xd0), ['No Peon Harvest', 'No Water / Unfloatable', 'Unamphibious']);
+    assert.deepStrictEqual(wpmCellRgb(0x0a), [255, 0, 255], 'primary pathing colors must remain RGB channels');
+    assert.notDeepStrictEqual(wpmCellRgb(0x80), [0, 0, 0], 'amphibious cells must not render as an anonymous black cell');
+}
+
 async function main() {
     testAssetPathNormalization();
     testSignals();
@@ -1128,6 +1145,7 @@ async function main() {
     testObjModDensityAndTreeStyling();
     testImportedAssetDedupeSafety();
     testLocalE2eFixturesRemainOptIn();
+    testWpmFlagSemantics();
     console.log('webview harness tests passed');
 }