Add cdac CCR instructions

.github/instructions/cdac.instructions.md

@@ -0,0 +1,34 @@
+---
+applyTo: "src/native/managed/cdac/**"
+---
+
+# cDAC — Folder-Specific Guidance
+
+## Preface
+
+The instructions under `API Review`, `DacDbi interface` and `Dump compatibility` only apply if the SDK version in global.json is a preview, release candidate or otherwise a development branch of .NET 11. If this is a development branch of .NET 12 or later, you **MUST** ignore these three sections entirely. Check `global.json` before applying them.
+
+## API Review (.NET 11 dev branches only)
+
+New APIs on implementations of IContract under the folder src/native/managed/cdac/Microsoft.Diagnostics.DataContractReader.Contracts/Contracts/** do **NOT** need to go through API review. **MUST NOT** describe such changes as "breaking" or "public API changes".
+
+## DacDbi interface (.NET 11 dev branches only)
+
+The DacDbi COM interface is **internal and unstable**.
+
+- **MUST NOT** flag changes to DacDbi as breaking changes.
+- **MUST NOT** warn about COM ABI compatibility, vtable ordering, or
+  GUID changes on DacDbi.
+
+## Dump compatibility (.NET 11 dev branches only)
+
+- **MUST NOT** raise concerns about older dumps lacking new data descriptors.
+- **MUST NOT** request fallback paths, conditional reads, or versioning
+  shims for missing descriptors on the grounds of "supporting older dumps".
+
+## Exception types
+
+When porting `HRESULT`-returning APIs to throw exceptions, the following mappings **MUST** be accepted:
+- `ArgumentException` → for `E_INVALIDARG`
+- `NullReferenceException` → for `E_POINTER`
+- `InvalidCastException` → for `E_NOINTERFACE`