fix(validate): reject condition edges routed on the wrong port field

src/error.rs

@@ -74,6 +74,31 @@ pub enum ValidationError {
         /// The highest schema version this crate understands.
         supported: u32,
     },
+
+    /// A `condition` node has an outgoing edge whose `from_port` is not one of
+    /// its two declared branch ports (`"true"` / `"false"`).
+    ///
+    /// Routing is keyed EXCLUSIVELY on `from_port` (see `engine::outgoing_by_port`
+    /// / `handler_routing`) — `to_port` is never consulted to decide which
+    /// successor fires. A condition node authored with the branch label on
+    /// `to_port` instead (e.g. `{from_port:"main", to_port:"true"}` and
+    /// `{from_port:"main", to_port:"false"}`) puts both edges in the SAME
+    /// `from_port` group, which `handler_routing` classifies as a parallel
+    /// `FanOut` — silently driving BOTH branches unconditionally instead of
+    /// gating on the condition's actual result. This is a HARD authoring
+    /// mistake, not a runtime data issue, so it is rejected here rather than
+    /// left as a silent no-op condition.
+    #[error(
+        "condition node {node} has an outgoing edge with from_port {from_port:?} — condition \
+         edges must emit on from_port \"true\" or \"false\" (the branch label belongs on \
+         from_port, not to_port; routing is keyed exclusively on from_port)"
+    )]
+    InvalidConditionRouting {
+        /// The offending condition node's id.
+        node: String,
+        /// The edge's actual (invalid) `from_port` value.
+        from_port: String,
+    },
 }
 
 /// Errors produced while compiling or running a workflow.
@@ -160,6 +185,16 @@ mod tests {
             "schema_version 5 is newer than this crate supports (max 1); \
              upgrade tinyflows to load this graph"
         );
+        assert_eq!(
+            ValidationError::InvalidConditionRouting {
+                node: "gate".to_string(),
+                from_port: "main".to_string(),
+            }
+            .to_string(),
+            "condition node gate has an outgoing edge with from_port \"main\" — condition \
+             edges must emit on from_port \"true\" or \"false\" (the branch label belongs on \
+             from_port, not to_port; routing is keyed exclusively on from_port)"
+        );
     }
 
     #[test]

src/validate.rs

@@ -113,6 +113,32 @@ pub fn validate(graph: &WorkflowGraph) -> Result<(), ValidationError> {
         }
     }
 
+    // A `condition` node's outgoing edges must emit on `from_port` "true" or
+    // "false" — routing is keyed EXCLUSIVELY on `from_port` (see
+    // `engine::outgoing_by_port` / `handler_routing`), so any other value
+    // (most commonly the default `"main"`, from an authoring mistake that put
+    // the branch label on `to_port` instead) is a hard authoring bug: it
+    // silently degrades to a parallel `FanOut` that drives BOTH branches
+    // unconditionally, with no runtime error or warning to point at the
+    // mistake. Caught here, at the door, instead.
+    let condition_node_ids: HashSet<&str> = graph
+        .nodes
+        .iter()
+        .filter(|n| n.kind == NodeKind::Condition)
+        .map(|n| n.id.as_str())
+        .collect();
+    for edge in &graph.edges {
+        if condition_node_ids.contains(edge.from_node.as_str())
+            && edge.from_port != "true"
+            && edge.from_port != "false"
+        {
+            return Err(ValidationError::InvalidConditionRouting {
+                node: edge.from_node.clone(),
+                from_port: edge.from_port.clone(),
+            });
+        }
+    }
+
     Ok(())
 }
 
@@ -457,6 +483,153 @@ mod tests {
         assert_eq!(validate(&graph), Ok(()));
     }
 
+    fn condition_node(id: &str) -> Node {
+        node(id, NodeKind::Condition)
+    }
+
+    #[test]
+    fn accepts_condition_with_branch_label_on_from_port() {
+        // The CORRECT shape (B23/B24): the branch label lives on `from_port`,
+        // `to_port` stays `"main"`.
+        let graph = WorkflowGraph {
+            nodes: vec![
+                node("t", NodeKind::Trigger),
+                condition_node("gate"),
+                node("yes", NodeKind::Agent),
+                node("no", NodeKind::Agent),
+            ],
+            edges: vec![
+                Edge {
+                    from_node: "t".to_string(),
+                    from_port: "main".to_string(),
+                    to_node: "gate".to_string(),
+                    to_port: "main".to_string(),
+                },
+                Edge {
+                    from_node: "gate".to_string(),
+                    from_port: "true".to_string(),
+                    to_node: "yes".to_string(),
+                    to_port: "main".to_string(),
+                },
+                Edge {
+                    from_node: "gate".to_string(),
+                    from_port: "false".to_string(),
+                    to_node: "no".to_string(),
+                    to_port: "main".to_string(),
+                },
+            ],
+            ..Default::default()
+        };
+        assert_eq!(validate(&graph), Ok(()));
+    }
+
+    #[test]
+    fn accepts_condition_with_only_one_branch_wired() {
+        // Wiring only the `true` (or only the `false`) branch is legal — the
+        // other simply dead-ends.
+        let graph = WorkflowGraph {
+            nodes: vec![
+                node("t", NodeKind::Trigger),
+                condition_node("gate"),
+                node("yes", NodeKind::Agent),
+            ],
+            edges: vec![
+                Edge {
+                    from_node: "t".to_string(),
+                    from_port: "main".to_string(),
+                    to_node: "gate".to_string(),
+                    to_port: "main".to_string(),
+                },
+                Edge {
+                    from_node: "gate".to_string(),
+                    from_port: "true".to_string(),
+                    to_node: "yes".to_string(),
+                    to_port: "main".to_string(),
+                },
+            ],
+            ..Default::default()
+        };
+        assert_eq!(validate(&graph), Ok(()));
+    }
+
+    #[test]
+    fn rejects_condition_with_branch_label_on_to_port_instead_of_from_port() {
+        // The BAD shape (B23/B24 — the exact bug the workflow_builder agent
+        // produced live): both edges share `from_port: "main"` with the branch
+        // label on `to_port` instead. Without this check, `handler_routing`
+        // would see one `from_port` group with two targets and classify it as
+        // a parallel `FanOut`, silently driving BOTH branches unconditionally.
+        let graph = WorkflowGraph {
+            nodes: vec![
+                node("t", NodeKind::Trigger),
+                condition_node("gate"),
+                node("yes", NodeKind::Agent),
+                node("no", NodeKind::Agent),
+            ],
+            edges: vec![
+                Edge {
+                    from_node: "t".to_string(),
+                    from_port: "main".to_string(),
+                    to_node: "gate".to_string(),
+                    to_port: "main".to_string(),
+                },
+                Edge {
+                    from_node: "gate".to_string(),
+                    from_port: "main".to_string(),
+                    to_node: "yes".to_string(),
+                    to_port: "true".to_string(),
+                },
+                Edge {
+                    from_node: "gate".to_string(),
+                    from_port: "main".to_string(),
+                    to_node: "no".to_string(),
+                    to_port: "false".to_string(),
+                },
+            ],
+            ..Default::default()
+        };
+        assert_eq!(
+            validate(&graph),
+            Err(ValidationError::InvalidConditionRouting {
+                node: "gate".to_string(),
+                from_port: "main".to_string(),
+            })
+        );
+    }
+
+    #[test]
+    fn rejects_condition_with_unrecognized_from_port() {
+        let graph = WorkflowGraph {
+            nodes: vec![
+                node("t", NodeKind::Trigger),
+                condition_node("gate"),
+                node("other", NodeKind::Agent),
+            ],
+            edges: vec![
+                Edge {
+                    from_node: "t".to_string(),
+                    from_port: "main".to_string(),
+                    to_node: "gate".to_string(),
+                    to_port: "main".to_string(),
+                },
+                Edge {
+                    from_node: "gate".to_string(),
+                    from_port: "maybe".to_string(),
+                    to_node: "other".to_string(),
+                    to_port: "main".to_string(),
+                },
+            ],
+            ..Default::default()
+        };
+        assert_eq!(
+            validate(&graph),
+            Err(ValidationError::InvalidConditionRouting {
+                node: "gate".to_string(),
+                from_port: "maybe".to_string(),
+            })
+        );
+    }
+
     #[test]
     fn duplicate_id_is_reported_before_trigger_checks() {
         // Two agents sharing an id and no trigger: the duplicate-id check runs