Save the build state before the source generation starts, so a generation cut short after it wrote layout.json runs again on the next try instead of being taken as done.

After Keep Build Cache removed the generated sources and the kit was updated, the lift ran because layout.json was
gone while its key still matched. An interruption after layout.json was back left the saved state calling the lift
complete, and the next run compiled unfinished sources. The pull request's two commits (one a merge of main) are
applied here as their net change.

Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>

tests/launcher_test.py

@@ -1554,13 +1554,14 @@ class MakeGameTest(Tmp):
         (kits[1] / 'runtime' / 'h.h').write_text('#define V 2\n')        # the new version changed the header
         self.assertEqual(go(kits[1])[:2], (1, 0))
 
-    def main_with(self, romfs, lift, compile_):
-        """make_game.main() in this process for a first build, with the given step functions in place of the real
+    def main_with(self, romfs, lift, compile_, rebuild=False):
+        """make_game.main() in this process, with the given step functions in place of the real
         lift and compile (they need real modules and clang). Returns the SystemExit code, or 0."""
         sys.path.insert(0, str(self.layout.pydeps))   # the fake zbic
         saved = (self.mg.step_romfs, self.mg.step_lift, self.mg.step_compile, sys.argv)
         self.mg.step_romfs, self.mg.step_lift, self.mg.step_compile = romfs, lift, compile_
-        sys.argv = ['make_game.py', '--nup', str(self.nup), '--out', str(self.out), '--msys', str(self.msys),
+        source = ['--rebuild'] if rebuild else ['--nup', str(self.nup)]
+        sys.argv = ['make_game.py', *source, '--out', str(self.out), '--msys', str(self.msys),
                     '--until', 'compile']   # the shaders step needs the shader translator
         try:
             with contextlib.redirect_stdout(io.StringIO()), contextlib.redirect_stderr(io.StringIO()):
@@ -1572,6 +1573,37 @@ class MakeGameTest(Tmp):
             self.mg.step_romfs, self.mg.step_lift, self.mg.step_compile, sys.argv = saved
             sys.path.remove(str(self.layout.pydeps))
 
+    def test_retry_interrupted_lift_after_cache_cleanup(self):
+        layout = self.out / 'build-cache' / 'lift' / 'layout.json'
+        ran = []
+
+        def lift(out, cache):
+            ran.append('lift')
+            layout.parent.mkdir(exist_ok=True)
+            layout.write_text('[]')
+
+        def compile_(out, cache, msys, jobs, romfs_job, update):
+            ran.append('compile')
+            self.assertTrue(layout.is_file())
+
+        def interrupted(out, cache):
+            lift(out, cache)
+            raise SystemExit(1)  # layout exists again, but the lift did not finish
+
+        with mock.patch.object(self.mg, 'WIN', True):  # use the fixture's MSYS toolchain check
+            self.assertEqual(self.main_with(self.mg.step_romfs, lift, compile_), 0)
+            self.nup.unlink()
+            ran.clear()
+            shutil.rmtree(layout.parent)
+            self.assertEqual(self.main_with(self.mg.step_romfs, lift, compile_, rebuild=True), 0)
+            self.assertEqual(ran, [])  # cleaning the cache alone does not require a compile
+
+            with mock.patch.object(self.mg, 'kit_version', return_value='updated kit'):
+                self.assertEqual(self.main_with(self.mg.step_romfs, interrupted, compile_, rebuild=True), 1)
+                self.assertEqual(self.main_with(self.mg.step_romfs, lift, compile_, rebuild=True), 0)
+                self.assertEqual(self.main_with(self.mg.step_romfs, lift, compile_, rebuild=True), 0)
+            self.assertEqual(ran, ['lift', 'lift', 'compile'])
+
     def test_romfs_beside_lift_and_compile(self):
         """A first build packs the RomFS image while the lift and the compile run; the compile gets the running step
         and waits for it only for the RomFS index."""

tools/make_game.py

@@ -2487,6 +2487,10 @@ def build_main():
                     for later in STEPS[STEPS.index(name):]:
                         if later == name or not ({name, later} & set(OWN_KEY_STEPS) or (name, later) in UNAFFECTED):
                             state['steps'].pop(later, None)
+                if name == 'lift':
+                    # The generator writes layout.json before the sources. A retry must finish an interrupted lift
+                    # even if the layout is back and the previous lift key still matches its inputs.
+                    save()
                 say(f'{name}:')
                 emit('step', step=name, state='start')
                 if name in ('shaders', 'prompts', 'scan') and romfs_job:   # they read the RomFS image