write_note: add guard against accidental overwrites

[bm-clawd]

Problem

write_note silently overwrites existing notes with the same title. This is dangerous for agents that accumulate content in files (daily notes, logs, journals). An agent calling write_note on a file that already exists loses all prior content.

Real-world example: an agent ran write_note on a daily memory file during reflection, destroying a full day of accumulated notes.

Proposal

Add an optional overwrite parameter (default: true for backwards compat):

• overwrite: true — current behavior (create or replace)
• overwrite: false — error if the note already exists

Alternatively, or additionally:

• mode: "create" | "update" | "upsert" for more granular control
• Return a warning/diff when overwriting a note that has changed since last read

Workaround

Agents should use edit_note with operation: "append" for any file that accumulates content. But the footgun remains for any agent that doesn't know this.

Context

The MCP write_note tool is the most natural first choice for agents — it's what they reach for. Making the destructive path require explicit opt-in would prevent data loss.

[claude]

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