[Luhaozhu]

Sandbox creation could reject concurrent requests while another container was starting, and a container removed during inventory enumeration could fail the entire request. This update moves capacity admission to a shared backend ledger, bounds concurrent creation, and tolerates containers disappearing during enumeration.

It also adds MCP OAuth client registration and private MCP connections, introduces native ACP client sessions, removes the Read-before-Edit precondition while retaining serialized mutations and unique text matching, and improves chat upload snapshots and My Space loading. The My Space changes overlap with #213.

Validation:

• CE brand, required-file, forbidden-artifact, license, import/OpenAPI/ORM, and release regression gates passed.
• The derived CE frontend production build passed.
• Sandbox regression suite: 80 passed.
• MCP OAuth, client-session, and file-edit regression suite: 40 passed in the product integration tree.
• Full frontend lint remains failing with 245 errors and 21 warnings on both the source baseline and product integration tree; the frontend file requiring conflict resolution passed targeted lint.

This branch contains only the derived community source tree and uses the public repository's history.