Sync: recursive updateApiObjectsNoChild ↔ updateApiMarkedBoards has no depth bound or cycle detection

[RodriSanchez1]

Part of #2195.

Problem

updateApiObjectsNoChild calls updateApiMarkedBoards (src/components/Board/Board.actions.js:1036), which in turn calls updateApiObjectsNoChild recursively when it finds shouldCreateBoard flags (:1086). Termination relies on the assumption that each recursion clears at least one flag, so the set of pending boards monotonically shrinks.

That assumption is informal:

• No explicit depth bound — a malformed graph (cyclic loadBoard references) could in principle keep marking boards.
• No telemetry to detect runaway cascades.
• The doc notes this in §14 with "Assumes finite board hierarchy depth."

In practice, the data model probably prevents cycles, so this is the lowest-priority item in the epic. But it's worth bounding defensively because the cost of a runaway loop is high (many API calls, possible stack overflow on deeply nested trees).

Proposed direction

• Add a recursion depth limit (e.g. 32) and log a warning if exceeded.
• Convert the recursion to an explicit work queue: collect all shouldCreateBoard and markToUpdate boards into a queue, drain iteratively. Combined with Sync: upsertApiCommunicator failures leave server-side communicator desynced silently #2197 (flags reflected in syncMeta) this becomes a normal Pass 1 push.

Acceptance criteria

• A pathological input does not produce unbounded recursion.
• Depth/iteration count is observable in logs.