Add a plan for working on the ledger blueprint

Author: Nicholas Clarke

src/ledger/README.md

@@ -2,7 +2,8 @@
 
 > [!WARNING]
 >
-> This blueprint is a work in progress.
+> This blueprint is a work in progress. See [./plan.md] for the intended
+> restructuring.
 
 The Ledger is responsible for validating Blocks and represents the actual
 semantics of Cardano transactions. The format of blocks and transactions is

src/ledger/plan.md

@@ -0,0 +1,52 @@
+# Ledger Blueprint Planning
+
+The aim is to restructure this documentation with the aim of providing a guide
+to somebody who might wish to implement the ledger for a compatible node.
+
+To that end, we break down the documentation in various sections. Certain
+things make sense to document in certain ways. We wish to avoid any duplication
+of work already done - for example, the formal specs remain probably the best
+way to document the precise implementation of a pure function. However, we can
+provide guidance for people trying to read the specifications.
+
+It is the fundamental nature of documentation to go out of date. As such, we
+also want to avoid referring to details of specific eras etc (which are in any
+case covered in the formal specs) and instead cover the general principles and
+details needed by all potential implementations.
+
+- Concepts
+  - Blocks
+    - The header/body split
+  - Transactions
+  - Eras
+  - The structure of an epoch
+- The ledger state transition
+  - How to read the specs
+    - Old-style semi-formal specs
+    - New-style Agda specifications
+- Ledger interfaces
+  - To the consensus layer
+    - Applying a block
+    - Ticking
+      - On an era boundary
+    - Forecasting
+    - Nonces
+    - The stake distribution
+  - To the mempool
+    - Validating a transaction
+    - Revalidating a transaction
+  - To the CLI
+    - Forecasting the leader schedule
+- Understanding parts of the transition
+  - Non-integral math
+  - Transaction fee calculation
+  - Reward calculation
+- Ledger serialisation
+  - Transaction and block formats
+  - The ledger state
+    - Decomposition - large and small parts
+- Constraints on the ledger
+  - Computational concerns
+    - Avoiding spikes
+  - Implications of the header/body split
+  - Rollbacks and storage