Add topdata bridge commands and handoff

README.md

@@ -35,6 +35,10 @@ tools/             built development binary output
 
 - `sow-module` uses `sow-toolkit` for `build-module`, `extract`, `validate`, `compare`, and `apply-hak-manifest`
 - `sow-assets` uses `sow-toolkit` for `build-haks` and validation
+- `sow-module` now also uses `sow-toolkit` for the early topdata bridge:
+  - `validate-topdata`
+  - `build-topdata`
+  - `compare-topdata`
 
 During development, sibling repositories can point at `../sow-tools/tools/sow-toolkit`. For pinned releases, each consumer repo can instead carry its own copy at `tools/sow-toolkit`.
 
@@ -50,3 +54,16 @@ Consumer repos can fetch those binaries into their local `tools/` directory with
 
 - `install-tool.sh` on Linux/macOS
 - `install-tool.ps1` on Windows
+
+## TopData Migration
+
+The topdata rebuild is now staged in this repo.
+
+Current state:
+
+- the new command surface exists in `sow-toolkit`
+- `sow-module/topdata/` is the new long-term source home
+- `build-topdata` currently bridges through the Python builder in `sow-dev` for authoritative output generation
+- native Go merge/build parity is still a follow-up milestone
+
+See [TOPDATA_HANDOFF_2026-04-02.md](./TOPDATA_HANDOFF_2026-04-02.md) for the current handoff and migration notes.