fix: detect generated asset manifest write failures before running the frontend manager.

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - fix: run manager commands in the configured root directory without changing the PHP working directory, and prevent manager probes and npm dependency cleanup when manager execution is disabled.
 - feat!: add secure frontend audits with CVE reporting, CI formats, and strict npm, pnpm, Yarn, and Bun validation.
 - perf: write generated Composer asset manifests directly without first copying their source files.
+- fix: detect generated asset manifest write failures before running the frontend manager.
 
 ## 0.2.0 January 24, 2026
 

src/Solver/Solver.php

@@ -213,6 +213,12 @@ private function getMockPackagePath(PackageInterface $package, string $assetDir,
 
         $targetJsonFile->write($packageValue);
 
+        if (!$targetJsonFile->exists()) {
+            throw new RuntimeException(
+                sprintf('Unable to write asset manifest "%s".', $newFilename),
+            );
+        }
+
         return [$packageName, $newFilename];
     }
 

tests/Solver/SolverTest.php

@@ -8,6 +8,7 @@
 use Composer\EventDispatcher\EventDispatcher;
 use Composer\Installer\InstallationManager;
 use Composer\IO\IOInterface;
+use Composer\Json\JsonFile;
 use Composer\Package\{Link, PackageInterface, RootPackageInterface};
 use Composer\Repository\{InstalledArrayRepository, RepositoryManager, WritableRepositoryInterface};
 use Composer\Semver\Constraint\Constraint;
@@ -20,6 +21,7 @@
 use Foxy\Fallback\FallbackInterface;
 use Foxy\FoxyEvents;
 use Foxy\Solver\{Solver, SolverInterface};
+use JsonException;
 use LogicException;
 use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\MockObject\MockObject;
@@ -824,6 +826,83 @@ public function testSolveRejectsWhitespaceOnlyAssetDirectory(): void
         $solver->solve($this->composer, $this->io);
     }
 
+    public function testSolveRestoresComposerWhenAssetManifestCannotBeRead(): void
+    {
+        $sourceContent = '{"name":"source-package","version":"1.0.0"}';
+        ['source' => $source, 'target' => $target] = $this->prepareAssetPackageManifest($sourceContent);
+
+        MockerState::addCondition(
+            'Foxy\\Solver',
+            'file_get_contents',
+            [$source, false, null, 0, null],
+            false,
+        );
+
+        $this->manager->expects(self::never())->method('addDependencies');
+        $this->manager->expects(self::never())->method('run');
+        $this->composerFallback->expects(self::once())->method('restore');
+
+        try {
+            $this->solver->solve($this->composer, $this->io);
+            self::fail('Expected reading the asset manifest to fail.');
+        } catch (RuntimeException $exception) {
+            self::assertSame(sprintf('Unable to read asset manifest "%s".', $source), $exception->getMessage());
+        }
+
+        self::assertSame($sourceContent, file_get_contents($source));
+        self::assertFileDoesNotExist($target);
+    }
+
+    public function testSolveRestoresComposerWhenAssetManifestCannotBeWritten(): void
+    {
+        $sourceContent = '{"name":"source-package","version":"1.0.0"}';
+        ['source' => $source, 'target' => $target] = $this->prepareAssetPackageManifest($sourceContent);
+        $targetContent = JsonFile::encode(
+            ['name' => '@composer-asset/foo--bar', 'version' => '1.0.0'],
+        ) . "\n";
+
+        MockerState::addCondition(
+            'Composer\\Json',
+            'file_put_contents',
+            [$target, $targetContent, 0, null],
+            false,
+        );
+
+        $this->manager->expects(self::never())->method('addDependencies');
+        $this->manager->expects(self::never())->method('run');
+        $this->composerFallback->expects(self::once())->method('restore');
+
+        try {
+            $this->solver->solve($this->composer, $this->io);
+            self::fail('Expected writing the asset manifest to fail.');
+        } catch (RuntimeException $exception) {
+            self::assertSame(sprintf('Unable to write asset manifest "%s".', $target), $exception->getMessage());
+        }
+
+        self::assertSame($sourceContent, file_get_contents($source));
+        self::assertFileDoesNotExist($target);
+    }
+
+    public function testSolveRestoresComposerWhenAssetManifestContainsInvalidJson(): void
+    {
+        $sourceContent = '{';
+        ['source' => $source, 'target' => $target] = $this->prepareAssetPackageManifest($sourceContent);
+
+        $this->manager->expects(self::never())->method('addDependencies');
+        $this->manager->expects(self::never())->method('run');
+        $this->composerFallback->expects(self::once())->method('restore');
+
+        try {
+            $this->solver->solve($this->composer, $this->io);
+            self::fail('Expected decoding the asset manifest to fail.');
+        } catch (JsonException $exception) {
+            self::assertSame('Syntax error', $exception->getMessage());
+        }
+
+        self::assertSame($sourceContent, file_get_contents($source));
+        self::assertFileDoesNotExist($target);
+    }
+
     public function testSolveRestoresComposerWhenManagerThrows(): void
     {
         $this->addInstalledPackages();
@@ -1045,4 +1124,38 @@ private function invokeSolverMethodOn(SolverInterface $solver, string $method, m
     {
         return (new ReflectionClass($solver))->getMethod($method)->invoke($solver, ...$arguments);
     }
+
+    /**
+     * @return array{source: string, target: string}
+     */
+    private function prepareAssetPackageManifest(string $sourceContent): array
+    {
+        $package = $this->createMock(PackageInterface::class);
+        $package->method('getName')->willReturn('foo/bar');
+        $package
+            ->method('getRequires')
+            ->willReturn([new Link('root/package', 'php-forge/foxy', new Constraint('=', '1.0.0'))]);
+
+        $this->addInstalledPackages([$package]);
+
+        $installPath = "{$this->cwd}/vendor/foo/bar";
+        $source = "{$installPath}/package.json";
+
+        $this->im->expects(self::once())->method('getInstallPath')->with($package)->willReturn($installPath);
+        $this->manager->expects(self::once())->method('getPackageName')->willReturn('package.json');
+        $this->sfs->mkdir($installPath);
+
+        self::assertNotFalse(file_put_contents($source, $sourceContent));
+
+        $source = realpath($source);
+
+        if (false === $source) {
+            self::fail('Unable to resolve the source asset manifest.');
+        }
+
+        return [
+            'source' => $this->fs->normalizePath($source),
+            'target' => $this->getCanonicalPath('/composer-asset-dir/foo/bar/package.json'),
+        ];
+    }
 }

tests/Support/InternalMockerExtension.php

@@ -40,6 +40,10 @@ public function notify(Finished $event): void
     public static function load(): void
     {
         $mocks = [
+            [
+                'namespace' => 'Composer\\Json',
+                'name' => 'file_put_contents',
+            ],
             [
                 'namespace' => 'Foxy\\Asset',
                 'name' => 'getcwd',