diff --git a/garnet.cabal b/garnet.cabal
index 981915b..296eb7e 100644
--- a/garnet.cabal
+++ b/garnet.cabal
@@ -6,6 +6,13 @@ author: Patrick Aldis
 maintainer:
     george.thomas@obsidian.systems
     patrick.aldis@obsidian.systems
+-- aha, nice, this does fix recompilation checking
+extra-source-files:
+    rust/target/debug/garnet_rs.h
+-- that could be problematic given file is gitignored? unfortunately this doesn't work
+-- tbf, I haven't even looked up the docs, just saw the autocompletion
+-- extra-tmp-files:
+--     rust/target/debug/garnet_rs.h
 
 common common
     default-language: GHC2024
@@ -43,6 +50,9 @@ library
         GarnetRs.Wrapped
     hs-source-dirs: lib
     include-dirs: rust/target/debug
+    -- HLS gives up entirely when the header is malformed if we do this
+    -- and anyway, I don't think it gives us dependency tracking like `extra-source-files` does
+    -- includes: garnet_rs.h
     extra-bundled-libraries: Cgarnet_rs
     build-depends:
         hs-bindgen,
diff --git a/lib/GarnetRs/Raw.hs b/lib/GarnetRs/Raw.hs
index 61312fa..a1e2dc1 100644
--- a/lib/GarnetRs/Raw.hs
+++ b/lib/GarnetRs/Raw.hs
@@ -29,7 +29,15 @@ import HsBindgen.TH
 import Language.Haskell.TH
 import System.Process
 
+import Control.Monad.IO.Class (MonadIO (liftIO))
+import Language.Haskell.TH.Syntax (addDependentFile)
+import System.Directory.Extra (getCurrentDirectory)
+
 do
+    -- not sure this does anything - hs-bindgen should already be doing the tracking, and the issues are from elsewhere
+    -- dir <- liftIO getCurrentDirectory
+    -- liftIO $ print dir
+    -- addDependentFile $ dir <> "/rust/target/debug/garnet_rs.h"
     systemDirs <- -- TODO bit of a hack
         map (Dir . T.unpack . T.strip)
             . concatMap (takeWhile (maybe False ((== ' ') . fst) . T.uncons) . dropWhile T.null . T.lines)
diff --git a/project.nix b/project.nix
index ffcffbe..cf124f0 100644
--- a/project.nix
+++ b/project.nix
@@ -19,6 +19,8 @@
   };
   overrides = [
     ({ pkgs, ... }: {
+      # TODO get this upstreamed:
+      # https://input-output-hk.github.io/haskell.nix/tutorials/pkg-map.html#mapping-in-haskellnix
       packages.libclang-bindings.components.library = {
         build-tools = [ pkgs.llvmPackages.llvm ];
         libs = [ pkgs.llvmPackages.libclang ];
diff --git a/rust/build.rs b/rust/build.rs
index d93e5bb..d875866 100644
--- a/rust/build.rs
+++ b/rust/build.rs
@@ -2,6 +2,22 @@ use std::env;
 use std::path::PathBuf;
 
 fn main() {
+    // this doesn't make _much_ difference really, since this is our only Rust source file
+    // but it seems it's probably better than not having it
+    // what we really want is to tell Rust to only regenerate the header file if the Rust code actually compiles
+    // but we don't have that flexibility
+    // and it's an issue because cbindgen tries to be fault-tolerant in some ways that don't even seem to make sense
+    //
+    // e.g. mis-spell "Option" as "Option" and you get
+    // void print_optional(Optio<const int8_t*> x);
+    // instead of
+    // void print_optional(const int8_t *x);
+    // and that's only an issue because in HLS TH dependent-file watching gives up after an error
+    // i.e. once the containing splice has thrown an exception once, the containing file needs a manual edit to kick it
+    // P.S. strings to stdout?! what a terrible API
+    // don't get me started in the discoverability of actually then using the terminal for debugging:
+    // println!("cargo::warning={:?}", env::var("OUT_DIR"));
+    println!("cargo::rerun-if-changed=lib.rs");
     let crate_dir = env::var("CARGO_MANIFEST_DIR").unwrap();
     let profile = env::var("PROFILE").unwrap();
     cbindgen::Builder::new()