feat(agent-toolkit): document the "group" filter column

[stasshw]

What

Documents the group filter column in three places. Descriptions only — no filtering behavior or schema-shape change.

• get_board_items_page description: a GROUP FILTERING section with the exact rule to use.
• filters[].columnId: states that group is accepted alongside real board column ids.
• get_column_type_info: returns filter guidelines for columnType: "group" (previously filter: null).

Why

Filtering by group has always worked — filters: [{"columnId": "group", "compareValue": ["group_mm6wsvcc"]}] — but it was documented nowhere, and get_board_info does not return group among a board's columns. Models could only get it right from prior knowledge of the monday API.

Meanwhile includeGroup hands the model each item's group.id. With no documented way to filter on it, models put the group id in filters[].columnId and got "Column not found".

Effect

Over 2 days, monday-agents caller:

• 21% of the tool's ResourceNotFoundException (500 of 2,367) — 40% excluding one runaway tenant
• 191 accounts affected
• 81% of failed group filters then scanned the whole board (351 of 431, ~2.9 extra calls each)

Notes

• Started larger and cut twice, deliberately. A groupIds parameter was dropped because the capability already exists in filters, a parameter is a permanent API commitment while a description is free to change, and groupIds next to columnIds would read like a projection rather than a filter. A server-side repair of misplaced group ids was dropped because it rewrites caller intent with nothing logged, and its value on top of the descriptions is unmeasured.
• Plan: re-measure this error code on the dashboard after release. Add a parameter or a repair only if the failures persist, with data behind it.
• The guidance says to use any_of / not_any_of for filtering by group id, rather than claiming those are the only supported operators — rule-engine-board-columns-config.json lists 10 for the group column. It recommends an array of ids without requiring one, since filter_rules_service.rb:70 applies Array.wrap.
• Group-only on purpose. Not here: the other non-column ids (__item_id__, __creation_log__, __last_updated__, 177 failures), oversized error messages, the hosted-mcp schema copy.
• 5.67.0 → 5.68.0. 1,336 tests pass.

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