fix: write-without-read validator now exempts control-flow branches

Operators with a `skip` field (inside if_/else_ branches) are mutually
exclusive at runtime, so writing the same field from different branches
is legitimate.  The validator now skips these ops when checking for
write-without-read violations.

Bump version to 0.2.4.

Author: Liam0205

apple/_version.py

@@ -1 +1 @@
-__version__ = "0.2.3"
+__version__ = "0.2.4"

apple/tests/test_validator.py

@@ -64,6 +64,22 @@ def test_read_then_write_ok(self):
                       function_for_common="g", function_for_item="")
         flow.compile()  # should not raise
 
+    def test_if_else_branches_write_same_field_ok(self):
+        """Mutually exclusive if/else branches may write the same field."""
+        flow = Flow(name="ok", common_input=["x"], common_output=["salt"])
+        flow.if_("x ~= nil") \
+            ._add_op("transform_by_lua",
+                     common_input=["x"], common_output=["salt"],
+                     lua_script="function f() return x end",
+                     function_for_common="f", function_for_item="") \
+        .else_() \
+            ._add_op("transform_by_lua",
+                     common_output=["salt"],
+                     lua_script="function g() return 'default' end",
+                     function_for_common="g", function_for_item="") \
+        .end_if_()
+        flow.compile()  # should not raise
+
 
 class TestDeadCode:
     def test_dead_operator(self):

apple/validator.py

@@ -102,12 +102,20 @@ def validate_write_without_read(
 ) -> None:
     """Detect writing a field that already exists (from upstream operator output)
     without reading it. Flow-contract inputs are not flagged — operators are
-    allowed to output fields that match flow inputs without reading them."""
-    # Track fields written by operators (not flow contract)
+    allowed to output fields that match flow inputs without reading them.
+
+    Operators inside a control-flow branch (``skip`` is set) are exempt from
+    *being flagged* AND their outputs do not count as "already written" for
+    downstream checks.  This is because mutually exclusive branches (if/else)
+    may legitimately write the same field without reading it."""
+    # Track fields written by operators (not flow contract).
+    # Only unconditional (non-skip) operators contribute.
     written_by_ops_common: set[str] = set()
     written_by_ops_item: set[str] = set()
 
     for name, op in ops:
+        if op.skip:
+            continue  # branch-internal ops are exempt
         for field in op.common_output:
             if field.startswith("_"):
                 continue

version.go

@@ -2,4 +2,4 @@ package pine
 
 // Version is the Pineapple engine version, embedded in every compiled JSON config.
 // This is the single source of truth — all Go code should reference this constant.
-const Version = "0.2.3"
+const Version = "0.2.4"