Fix the remote build of CA derivations

Make sure that the derivation we send to the remote builder is exactly
the one that we want to build locally so that the output ids are exactly
the same

Fix #4845

src/build-remote/build-remote.cc

@@ -277,6 +277,15 @@ connected:
 
         auto drv = store->readDerivation(*drvPath);
         auto outputHashes = staticOutputHashes(*store, drv);
+
+        // Hijack the inputs paths of the derivation to include all the paths
+        // that come from the `inputDrvs` set.
+        // We don’t do that for the derivations whose `inputDrvs` is empty
+        // because
+        // 1. It’s not needed
+        // 2. Changing the `inputSrcs` set changes the associated output ids,
+        //  which break CA derivations
+        if (!drv.inputDrvs.empty())
             drv.inputSrcs = store->parseStorePathSet(inputs);
 
         auto result = sshStore->buildDerivation(*drvPath, drv);