Initial import of the CBDDC codebase with docs and tests. Add a .NET-focused gitignore to keep generated artifacts out of source control.

docs/peer-deprecation-removal-runbook.md

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+# Peer Deprecation & Removal Runbook
+
+Operational workflow for safely deprecating or removing peers in clusters using
+peer-confirmed pruning.
+
+## When to use this runbook
+
+- A site is permanently decommissioned.
+- A peer has been unreachable long enough to block prune progress.
+- A peer is being replaced and should stop gating prune decisions.
+
+## Decision matrix
+
+| Scenario | Action |
+|------|-----------|
+| Peer is temporarily offline and expected to return soon | Keep tracking; monitor lag and confirmations. |
+| Peer should stay configured but must stop gating pruning | `RemovePeerTrackingAsync(nodeId, removeRemoteConfig: false)` |
+| Peer is permanently removed from topology | `RemoveRemotePeerAsync(nodeId)` |
+
+## Procedure
+
+1. Confirm peer intent (temporary outage vs. decommission).
+2. Inspect health payload:
+   - `peersWithNoConfirmation`
+   - `laggingPeers`
+   - `lastSuccessfulConfirmationUpdateByPeer`
+3. If deprecating from prune gating only, run:
+
+```csharp
+await peerManagement.RemovePeerTrackingAsync(
+    nodeId: "peer-to-deprecate",
+    removeRemoteConfig: false,
+    cancellationToken);
+```
+
+4. If permanently removing, run:
+
+```csharp
+await peerManagement.RemoveRemotePeerAsync("peer-to-remove", cancellationToken);
+```
+
+5. Re-check `/health` and verify status transition:
+   - `Degraded`/`Unhealthy` should clear if the removed peer was the cause.
+6. Confirm maintenance logs no longer report prune blocking for that peer.
+
+## Post-change verification
+
+- Peer no longer appears in active tracked peers.
+- `maxLagMs` trends with only current active peers.
+- Pruning resumes with a valid effective cutoff (or a known non-peer reason).
+
+## Emergency path
+
+If pruning is blocked and storage pressure is high:
+
+1. De-track the clearly retired peer first (`removeRemoteConfig: false`).
+2. Validate pruning resumes.
+3. Perform full peer removal after change-control approval.
+
+## Re-activation path
+
+If a deprecated peer returns and should gate pruning again:
+
+1. Ensure peer config is enabled/available.
+2. Allow sync to re-register and refresh confirmations.
+3. Watch health payload until peer exits `peersWithNoConfirmation`.