docs: add CLAUDE.md with rain.flare build invariants (#74)

CLAUDE.md

@@ -0,0 +1,19 @@
+# rain.flare — build invariants
+
+## Committed artifacts — regenerate with build.sh
+
+`meta/FlareFtsoSubParserAuthoringMeta.rain.meta` and `meta/FlareFtsoWords.rain.meta` are generated outputs, not hand-edited. Run `./script/build.sh` to regenerate them and commit the result. If they drift, `copy-artifacts` CI fails.
+
+`src/generated/FlareFtsoWords.pointers.sol` is also a generated artifact, regenerated by the nix prelude (`rain-flare-prelude`). Regenerate via `nix develop -c rain-flare-prelude` and commit the result alongside the meta files.
+
+## Build tools
+
+Use `nix develop` for all builds. `forge` and `rain` binaries must come from the nix shell — do not use system-installed versions.
+
+## Dependencies
+
+Soldeer (not git submodules). Run `forge soldeer install` inside `nix develop` to install/update dependencies listed in `foundry.toml`.
+
+## Publishing
+
+Pushing to `main` automatically publishes the soldeer package via `rainix-autopublish`. No manual publish step.

REUSE.toml

@@ -6,6 +6,7 @@ path = [
   ".github/workflows/**/",
   ".gitignore",
   ".soldeerignore",
+  "CLAUDE.md",
   "README.md",
   "flake.lock",
   "flake.nix",