add cached processes tutorial

tutorials/03-advanced/04-cached-processes/README.md

@@ -0,0 +1,28 @@
+# Using cached processes
+
+When you run an inventory or impact assessment, the engine builds a system of equations that represents all processes and their dependencies.  
+This system is then solved in one pass to compute the results.
+
+For small models this is fine, but for large models the system can grow very large, making the solve more costly.
+
+The `@cached` annotation helps here: it tells the engine to **pre-solve a subsystem** (a process and its dependencies) during runtime.  
+The result of this local solve is then reused in the global assessment.  
+This makes the final system smaller and the overall computation faster while giving exactly the same results.
+
+## Try it yourself
+
+The file `main.lca` defines a `bake` process annotated with `@cached`.
+
+Run the following command once with the annotation, and once without:
+
+```bash
+lcaac trace sandwich_factory
+```
+
+Compare the two results:
+
+Without `@cached`, you will see `flour_production` and `salt_production` listed as dependencies of `sandwich_factory`.
+
+With `@cached`, these dependencies disappear from the trace. They are pre-solved and collapsed into the `bake` process.
+
+The impacts remain the same in both cases. Only the solving pipeline changes.

tutorials/03-advanced/04-cached-processes/main.lca

@@ -0,0 +1,56 @@
+process sandwich_factory {
+    products {
+        1 u sandwich
+    }
+    inputs {
+        200 g bread
+        50 g ham
+    }
+}
+
+@cached
+process bake {
+    products {
+        1 kg bread
+    }
+    inputs {
+        1 kg flour
+        30 g salt
+    }
+}
+
+process flour_production {
+    products {
+        1 kg flour
+    }
+    impacts {
+        2 kg_CO2_Eq GWP
+    }
+}
+
+process salt_production {
+    products {
+        1 g salt
+    }
+    impacts {
+        0.05 kg_CO2_Eq GWP
+    }
+}
+
+process ham_production {
+    products {
+        1 g ham
+    }
+    impacts {
+        0.7 kg_CO2_Eq GWP
+    }
+}
+
+test main_with_mock_data {
+    given {
+        1 u sandwich from sandwich_factory
+    }
+    assert {
+        GWP between 35.6 kg_CO2_Eq and 35.7 kg_CO2_Eq
+    }
+}

tutorials/run.sh

@@ -36,6 +36,8 @@ lcaac test -p $TUTORIALS_PATH/03-advanced/02-circular-footprint-formula
 lcaac test -p $TUTORIALS_PATH/03-advanced/03-project-file/lcaac.yaml main_with_data
 lcaac test -p $TUTORIALS_PATH/03-advanced/03-project-file/lcaac-mock.yaml main_with_mock_data
 
+lcaac test -p $TUTORIALS_PATH/03-advanced/04-cached-processes
+
 # Check custom dimensions tutorial
 set -euo
 # The following assessment is expected to fail.