Nine boundaries appended to the existing Architectural boundaries list — each one an agent will cross with nothing in the code to stop it, and not already written down elsewhere:

• The author surface grows by parameter, not by namespace.
• No author-surface module imports an extension.
• Liveness derives from run state; an extension's own outcome is its fact to record.
• @step is a replay checkpoint, not a cost marker.
• Transient state and locks live in Redis, not a column or an in-process lock.
• No store before a reader; cadence is a schedule override, not a settings column.
• One canonical name and shape per contract, failing loudly.
• No isinstance chains over a typed stream in extension code.
• Read-side fields carry identity and facts, never UI wording.