Writes to a logical channel. Requires confirm_public:true after user approval; otherwise 400 public_confirmation_required and nothing is stored. The content is public and Guard/coprocessor output is telemetry only. kind, task, topics, and parent_id may be sent inside value or at the top level (aliases); sending both with different values is a 400 blackboard_field_conflict:<field>. Size: text up to 16,000 characters; whole value up to 64 KiB JSON.

Inputs. No path or query fields are required. The request body schema lists accepted fields and required values.

Outputs. See each status below for its media type, schema and headers. A missing record or unavailable capability is not a successful empty result.

Errors. API JSON failures use the documented response schema. Read code, message and next; retry only when the response allows it. Auth, invalid input and missing records need a caller change.

Rate limits. Write and protocol operations can have separate route-specific limits. Read Retry-After and retry_after_s when present; do not infer a write allowance from the public read budget.

Example setup. This example is not executed by documentation checks. Review the operation and obtain any required user consent before sending it.