Why

Memory clients sometimes need to continue reading a file from a known line instead of starting over from the top. Adding a line offset to the read MCP keeps that resume logic simple and avoids re-reading already-consumed content.

What changed

• Added an optional line_offset argument to the memory read tool, defaulting to 1.
• Read content starting at the requested 1-indexed line before token truncation, and return start_line_number in the response.
• Treat invalid offsets as invalid params errors and cover the new behavior in codex-rs/memories/mcp/src/local_tests.rs.

Testing

• Added unit tests for reading from a non-default starting line.
• Added unit tests for rejecting 0 and past-end line offsets.