Implement checkpoint modes with docs/tests and reorganize project file layout

README.md

@@ -104,6 +104,27 @@ Operational procedures, diagnostics, and escalation are documented in:
 - [`docs/runbook.md`](docs/runbook.md)
 - [`docs/troubleshooting.md`](docs/troubleshooting.md)
 
+## Checkpoint Modes
+
+`DocumentDbContext` and `StorageEngine` support explicit checkpoint modes via `CheckpointMode`:
+
+- `Passive`: non-blocking; skips if checkpoint lock is contended.
+- `Full`: applies committed WAL pages and appends a checkpoint marker, without truncating WAL.
+- `Truncate`: applies committed WAL pages and truncates WAL.
+- `Restart`: truncate + WAL writer restart.
+
+Example:
+
+```csharp
+using ZB.MOM.WW.CBDD.Core.Transactions;
+
+var result = db.Checkpoint(CheckpointMode.Full);
+if (!result.Executed)
+{
+    // passive checkpoint can be skipped under contention
+}
+```
+
 ## Security And Compliance Posture
 
 - CBDD relies on host and process-level access controls.