page set: doesn't support relation properties (error message doesn't suggest page link)

[DidelotK]

Description

notion page set <id> "MyRelation=<related-page-id>" fails with:

Error: set properties: validation_error: <RelationField> is expected to be relation.

This is technically working as documented (the canonical commands are notion page link / unlink), but two UX gaps:

1. The error message doesn't suggest notion page link --prop "MyRelation" --to <id> — users have to dig into docs to find the right command
2. notion page set accepts every other property type via Key=Value syntax. Excluding relations breaks the mental model — users reasonably expect "set this property to this value" to work uniformly

Repro

notion page set <page-id> "Product categories=34bd580f-96c5-80f7-9dee-d188f1cb4564"
# → Error: set properties: validation_error: Product categories is expected to be relation.

Expected

Either:

1. Make page set work for relations — accept comma-separated page IDs for multi-relation, single ID for single-relation. This is the most intuitive.
2. Improve the error message to direct users to page link — minimum bar to avoid wasting time.

Ideally (1), since the syntax already supports comma-separated values for other multi-value properties (e.g., Tags=a,b,c for multi_select).

Environment

• notion-cli v0.7.0

Impact

Minor surprise + extra trip to docs. Doesn't block anything but breaks the "uniform interface" expectation.