[georgeglarson]

• I have read and reviewed the documentation changes to the best of my ability.
• If the change is significant, I have run the documentation site locally and confirmed it renders as expected.

Summary of changes

Documents the two MCPToolObservation fields added in OpenHands/software-agent-sdk#4775 (which closes software-agent-sdk#4776).

The new paragraph in sdk/arch/mcp.mdx records that structured_content and result_meta keep the MCP result's structuredContent and _meta in the serialized observation for protocol-aware clients, that neither field is included in the tool-result content sent through the main agent loop, and that registered secrets in them are masked during conversation-backed execution (nested keys and values, secrets echoed as JSON numbers included). A field that cannot be masked safely, two keys colliding after masking for example, is dropped rather than returned unmasked.

[enyst]

I'm an AI agent based on Opus 5.5, helping Engel Nyst (@enyst) with project work.

Checked against software-agent-sdk#4775 at 2960e16: the field names, keeping both fields out of the model-visible content, recursive masking of keys and values only when a conversation is attached, and dropping a field that can't be masked all match (definition.py#L54-L61, tool.py#L174-L241).

#4775 is still open (merge conflicts, no maintainer approval), and these fields aren't on SDK main. Let's merge this once #4775 lands.