Define complete Rust API mapping schema

RUSTREWRITE.md

@@ -22,8 +22,11 @@ Generated inventories are intentionally checked in:
   projects, including a SHA-256 digest.
 - `api/public-api.json` is the authoritative compiled-metadata catalog for all
   13 library assemblies after all six source generators run. It also records
-  every external type referenced by a public signature as a pending Rust
-  mapping obligation.
+  every external type referenced by a public signature.
+- `api/RUST-TYPES.tsv` resolves all 3,066 public and 142 external signature
+  types, plus two support traits referenced by public inheritance metadata.
+- `api/RUST-MAPPING.tsv` records the reviewed Rust destination and complete
+  signature decision for all 30,789 public members.
 - `tests/upstream-tests.json` records every NUnit invocation and the SHA-256 of
   its C# method body.
 - `tests/PARITY.md` maps every NUnit invocation to its Rust test name.
@@ -45,8 +48,8 @@ The current workspace is a structural baseline, not a working client:
 - 1,705 public C# type declarations produce compiling Rust type/trait shims;
 - 12,195 public declaration lines are retained in the API ledger;
 - compiled metadata records 3,066 public types and 30,789 public members with
-  matching independent ECMA-335 counts, plus 142 external signature types that
-  still require explicit Rust mapping decisions;
+  matching independent ECMA-335 counts, with all 142 external signature types
+  resolved to cross-platform Rust or project-owned boundary types;
 - all 1,295 NUnit `[Test]`/`[TestCase]` invocations have compiling Rust test
   entries that intentionally panic with their source identity and body hash;
 - all nine sample/tool projects have compiling Rust binary targets;
@@ -166,6 +169,33 @@ Apply these rules consistently:
 | vectors/quaternions/matrices | compatibility structs with LibreMetaverse field/order semantics; use `glam` internally after parity tests prove conversions |
 | dependency injection container | normal constructors and explicit trait parameters; add no service-locator equivalent |
 
+The checked-in mapping ledgers make those rules concrete:
+
+- properties become getter/setter methods; indexers become `item`/`set_item`
+  methods with their index parameters;
+- events become typed subscriptions returning a guard; stored delegates become
+  `Fn` callbacks, while CLR `BeginInvoke`/`EndInvoke` rows are retained as
+  intentional differences;
+- `in` borrows immutably, `ref` borrows mutably, and `out` is a mutable output;
+  optional parameters use `Option<T>` rather than Rust default arguments;
+- nullable values use `Option<T>` at the exact metadata node, including nested
+  generic arguments;
+- inheritance maps to traits and composition rather than class inheritance;
+  generic parameters retain their names and cataloged constraints as explicit
+  Rust bounds recorded in the mapping ledgers;
+- operators receive stable trait-style names; overloads receive parameter-based
+  descriptive suffixes and a stable ID suffix only when necessary;
+- `[Flags]` enums use `bitflags` with unknown bits retained; wire enums use their
+  exact width/discriminants and an `Unknown(raw)` form only when extensible;
+- all third-party types exposed by C# signatures map through project-owned
+  cross-platform boundary types. No mapping may name a macOS-only API unless
+  equivalent Linux and Windows implementations are provided.
+
+Run `python3 tools/generate_rust_mapping.py --check` after any catalog or mapping
+rule change. It regenerates in memory and rejects duplicate source IDs or Rust
+destinations, stale/missing members, unresolved referenced types, invalid
+statuses, missing assembly representatives, and platform-specific targets.
+
 Public structs and enums that come from the protocol must be `#[non_exhaustive]`
 when servers may add values. Do not derive `Serialize`/`Deserialize` as a
 substitute for the specified wire encoding: LLUDP, LLSD, MessagePack, asset