fix handling of index-state

Author: andreabedini

Makefile

@@ -969,9 +969,14 @@ _build/bindist/tests.tar.gz:
 
 $(GHC1) $(GHC2): | hackage
 hackage: _build/packages/hackage.haskell.org/01-index.tar.gz
+
+# Always run cabal update. This makes sure that the index file won't go stale,
+# whatever index-state we set in the project file. Reproducibility is left to
+# index-state.
+.PHONY: _build/packages/hackage.haskell.org/01-index.tar.gz
 _build/packages/hackage.haskell.org/01-index.tar.gz: | $(CABAL)
 	@mkdir -p $(@D)
-	$(CABAL) $(CABAL_ARGS) update --index-state @1745256340
+	$(CABAL) $(CABAL_ARGS) update
 
 # --- Configure and source preparation ---
 

cabal.project.stage1

@@ -1,3 +1,5 @@
+index-state: 2025-10-26T19:17:08Z
+
 packages:
   -- NOTE: we need rts-headers, because the _newly_ built compiler depends
   --       on these potentially _new_ headers, we must not rely on those from
@@ -37,6 +39,7 @@ packages:
   utils/ghc-toolchain
   utils/ghc-toolchain/exe
 
+
 benchmarks: False
 tests: False
 allow-boot-library-installs: True