Add Anthropic Files API and persistent Google file caching for all providers

- Add anthropic_file_id/google_file_uri fields to FileMeta (backend + frontend)
- Eager upload to Anthropic and Google at file upload time (like OpenAI)
- Cache and reuse file references in prepare_attachments for all 3 providers
- Add document content block injection in stream_claude (file_id, base64, text fallback)
- Conditional beta streaming for Anthropic Files API references
- Persist on-demand upload results (changed flag + save_files_index)
- Clean up file deletion for all providers (Anthropic warn-only, Google deduplicated)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/frontend/src/store/flowStore.ts b/frontend/src/store/flowStore.ts
index 665030b..6140339 100644
--- a/frontend/src/store/flowStore.ts
+++ b/frontend/src/store/flowStore.ts
@@ -129,6 +129,8 @@ export interface FileMeta {
   created_at: number;
   provider?: string;
   provider_file_id?: string;
+  anthropic_file_id?: string;
+  google_file_uri?: string;
   scopes?: string[];  // "project_path/node_id" composite keys
 }