Add downloadUrl (presigned URL) to generate_pptx response

[okamoto-aws]

Summary

Add a downloadUrl (S3 presigned URL) to the generate_pptx MCP tool response in the Remote MCP Server (Layer 3).

Motivation

When integrating with external platforms like GenU (Generative AI Use Cases), the caller has no direct access to S3 or the SDPM Web UI. The current response only returns status and slide summary — there is no way for the caller to retrieve the generated PPTX file.

Adding a presigned URL enables external MCP clients to provide a download link directly to the end user.

Current behavior

generate_pptx returns:

{
  "status": "completed",
  "slideCount": 12,
  "slides": ["page01 - Title", "..."]
}

Proposed behavior

{
  "status": "completed",
  "slideCount": 12,
  "slides": ["page01 - Title", "..."],
  "downloadUrl": "https://bucket.s3.region.amazonaws.com/pptx/deck-id/uuid.pptx?X-Amz-..."
}

Implementation

In mcp-server/tools/generate.py, after uploading the PPTX to S3:

result["downloadUrl"] = storage.presign_url(key=key, expires=3600)

Storage.presign_url() already exists in the ABC and is implemented in AwsStorage.

Scope

• Only affects Remote MCP Server (mcp-server/tools/generate.py)
• Local MCP Server (mcp-local/) is unaffected (separate codebase, returns local file path)
• No breaking change — additive field only

[okamoto-aws]

Since the downloadUrl is usually too long to receive and handle as LLM context, we will consider adding a simple frontend to download the prepared PPTX file.