add matrix orchestrator rail and repo scaffolding

README.md

@@ -127,6 +127,22 @@ Templates currently supported:
 - `typescript-nextjs`
 - `monorepo`
 
+## Matrix Orchestrator Rail
+
+Mosaic includes a runtime-agnostic orchestrator rail at:
+
+- `~/.mosaic/rails/orchestrator-matrix/`
+
+Run from a bootstrapped repo:
+
+```bash
+~/.mosaic/bin/mosaic-orchestrator-run --once
+~/.mosaic/bin/mosaic-orchestrator-run --poll-sec 10
+```
+
+The controller reads/writes repo-local state in `.mosaic/orchestrator/` and emits
+structured events to `.mosaic/orchestrator/events.ndjson` for Matrix bridge consumption.
+
 ## Bootstrap Any Repo (Slave Linkage)
 
 Attach any repository/workspace to the master layer: