fix: reject config writes without a revision

Issue: #340
User-Visible: yes

test/coordinate-write-barrier-guard.test.mjs

@@ -1,4 +1,9 @@
 import assert from 'node:assert/strict';
+import {
+  mkdirSync, mkdtempSync, readFileSync, readdirSync, rmSync, writeFileSync,
+} from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join, resolve } from 'node:path';
 import test from 'node:test';
 import { fileURLToPath } from 'node:url';
 
@@ -9,3 +14,38 @@ const repoRoot = fileURLToPath(new URL('..', import.meta.url));
 test('all frontend and backend coordinate writers converge on one boundary (#291)', () => {
   assert.deepEqual(checkCoordinateWriteBarriers(repoRoot), []);
 });
+
+test('the canonical config writer cannot drop its expected revision (#340)', () => {
+  const fixtureRoot = mkdtempSync(join(tmpdir(), 'houseplan-config-rev-'));
+  try {
+    mkdirSync(resolve(fixtureRoot, 'src'), { recursive: true });
+    mkdirSync(resolve(fixtureRoot, 'custom_components/houseplan'), { recursive: true });
+    for (const name of ['houseplan-card.ts', 'houseplan-editor-runtime.ts']) {
+      writeFileSync(
+        resolve(fixtureRoot, 'src', name),
+        readFileSync(resolve(repoRoot, 'src', name), 'utf8'),
+      );
+    }
+    const componentRoot = resolve(repoRoot, 'custom_components/houseplan');
+    for (const name of readdirSync(componentRoot).filter((entry) => entry.endsWith('.py'))) {
+      writeFileSync(
+        resolve(fixtureRoot, 'custom_components/houseplan', name),
+        readFileSync(resolve(componentRoot, name), 'utf8'),
+      );
+    }
+
+    const cardPath = resolve(fixtureRoot, 'src/houseplan-card.ts');
+    const productionCard = readFileSync(cardPath, 'utf8');
+    const withoutRevision = productionCard
+      .replace(', expected_rev: this._cfgRev', '');
+    assert.notEqual(withoutRevision, productionCard, 'fixture must remove the revision field');
+    writeFileSync(cardPath, withoutRevision);
+
+    assert.ok(
+      checkCoordinateWriteBarriers(fixtureRoot)
+        .includes('frontend config/set bypasses the canonical boundary'),
+    );
+  } finally {
+    rmSync(fixtureRoot, { recursive: true, force: true });
+  }
+});