open_presentation with SharePoint URL does not maintain file handle

[chillinbg]

Describe the bug
When opening a SharePoint-hosted .pptx via open_presentation with an HTTPS SharePoint URL, the tool returns "Presentation opened successfully" but does not maintain a persistent file handle. Any subsequent call returns "No presentation is open." The success response is misleading -- the file is not actually held open across calls.

To Reproduce

Call open_presentation with a SharePoint HTTPS URL (e.g. https://[tenant].sharepoint.com/sites/[site]/Shared%20Documents/file.pptx)
Observe "Presentation opened successfully"
Immediately call save_presentation or add_text_to_slide
Observe "No presentation is open"

Expected behavior
The presentation remains open and accessible for subsequent tool calls within the same session.

Logs
open_presentation response: "Presentation opened successfully"
save_presentation response: "No presentation is open"

Additional context
This makes the PowerPoint MCP non-functional for SharePoint-hosted files, which is the primary enterprise use case. The tool works correctly when opening local files.