basecamp mcp: replace actions clear any field an agent leaves out, so a title-only edit wipes the to-do #895

Context

Found while evaluating basecamp mcp as a replacement for dyve/basecamp-cli-mcp, a self-built MCP server, written with Claude, that wraps the basecamp CLI. It exists because we wanted read/write Basecamp access from Claude Cowork and Claude Desktop, which have no terminal for the CLI or the Basecamp skill. Now that the CLI ships its own MCP server, we would rather use that than maintain ours; this issue is one of the gaps in the way.

basecamp-cli-mcp gets merge-safe edits by calling todos update / files update, so a title-only update leaves the rest of the record intact.

What happens

basecamp_todos exposes only replace_todo for editing a to-do. Its describe text says the body is the full writable state and that any omitted field is cleared. That is accurate, but an agent only sees it if it calls describe before writing. The action list shows just "Replace a todo with a new complete representation". The natural call for "rename this to-do" sends only content, and it destroys the rest of the record.

Repro (v0.13.2, macOS, Basecamp 3 account)

1. basecamp_todos → create_todo with content, description: "<div>keep me</div>", due_on: "2026-12-01", assignee_ids: [<person>].
2. basecamp_todos → replace_todo with { "todoId": <id>, "content": "renamed" }.
3. Read it back: description is "", due_on is gone, assignees is [].

replace_document documents the same behavior: omitting content clears the body, and omitting title leaves an "Untitled" document. Per the action catalog, replace_schedule_entry and update_todolist_or_group ("Replace a todolist…") are also full-replace operations. I verified only replace_todo live.

Why it matters for MCP specifically

The CLI does not have this problem: basecamp todos update <id> --title x and basecamp files update <id> --title x leave the other fields intact. Agents moving from the CLI, or from the Basecamp skill, to basecamp mcp will reasonably expect the same, and the failure is silent and destructive.

Suggestion

Offer a merge-safe update action next to each replace action, for example a synthetic update_todo that reads the record and merges in the given fields before the PUT. That is what the CLI's update commands already do, and the synthetic mentions parameter on create_comment shows the gateway already supports client-side composition. At minimum, the one-line action summary should say that omitted fields are cleared, since that line is all an agent sees without calling describe.

AI disclosure

This issue was discovered and described with assistance from Claude Code.