v0.5.1 - ACM-7: Pinned messages survive compaction
ACM-7: Re-inject pinned messages across compaction boundaries
Pinned messages pushed before a compaction boundary were silently absent from the model's context after compaction. The transform hook now fetches and prepends any pinned messages missing from output.messages, with a synthetic marker so agents can identify them as re-injected context.
This was the core ACM contract violation — it is now fixed.