Implementation Log: Start multi-file upload (US-04)

Feature: Start multi-file upload

Summary

Implemented a batch-aware startUpload flow that initiates multi-file uploads. The server creates pending Asset records per file, requests storage upload targets (one target per chunk), and returns per-file upload grants and targets. Whole-request validation is returned as top-level userErrors; per-file problems are reported per-file.

Implementation Details

• StartUploadService::startUploadBatch validates the batch, creates pending assets, asks the StorageAdapter for upload targets, and issues per-file upload grants.
• GraphQL schema extended with StartUploadBatchInput/StartUploadBatchPayload and a StartUploadBatchResolver maps the application result into the GraphQL response.
• MockStorageAdapter provides deterministic mock:// upload targets for local development so no external storage is required.

Files Changed

• src/Application/Asset/StartUploadService.php — batch start implementation
• src/Application/Asset/Command/StartUploadBatchCommand.php — command for batch start
• src/Application/Asset/Result/StartUploadBatchResult.php — batch result shape
• src/GraphQL/Resolver/StartUploadBatchResolver.php — GraphQL mapping
• src/GraphQL/Schema/schema.graphql — schema additions for batch upload
• src/Infrastructure/Storage/MockStorageAdapter.php — local target generation
• tests/Unit/Application/Asset/StartUploadServiceTest.php — unit tests
• tests/Unit/Http/GraphQLHandlerTest.php — GraphQL mapping tests

Validation

• vendor/bin/phpunit --configuration phpunit.xml tests/Unit/Application/Asset/StartUploadServiceTest.php — passed locally (unit tests).
• vendor/bin/phpunit --configuration phpunit.xml tests/Unit/Http/GraphQLHandlerTest.php — passed locally.
• Integration tests that require MySQL were skipped locally due to the test database not being available.

Follow-up

• Run the full CI pipeline and mkdocs build in an environment with MkDocs installed to confirm navigation and link rendering.
• Optionally add an integration smoke test for storage target generation.