## What changed
Add `codex-message-board-mcp` with a `MessageBoardMcpServer` that exposes selected message-board tools through `rmcp::ServerHandler`. Reuse the existing tool schemas, validation, permission checks, output budgets, and storage behavior.
Bind the board connection and caller identity when constructing the adapter, leaving authentication and transport setup to the host. Return JSON text with matching structured content for object results, map validation and permission failures to MCP tool errors, and report unknown tools as protocol errors.
Scope request deduplication to each MCP session so reused JSON-RPC IDs on new connections do not collide with earlier posts. Preserve the distinction between numeric and string request IDs.
## Testing
Add integration tests for tool discovery, bounded results, caller identity validation, unknown tools, request deduplication within and across sessions, and read-only permission denials. Exercise discovery and calls against both local and in-memory boards.
GitOrigin-RevId: 6c62c340b24198a00d0d3d0487cb2ebc5c397b06
## What changed
Move the message-board API, types, permissions, storage backends, and tool implementations into the new `codex-message-board` crate. Keep extension registration in `codex-agent-message-board-extension`, and update core and the remote client to use the shared crate directly.
Move the existing board tests with the implementation and add the crate to the Cargo workspace and Bazel build.
GitOrigin-RevId: 33ce527c2bef7f862eba55cb9b32222902ccf4ad
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