diff --git a/lib/components/fabro-tool/src/workflow_version.rs b/lib/components/fabro-tool/src/workflow_version.rs
index 8adb193f8..38be81c8b 100644
--- a/lib/components/fabro-tool/src/workflow_version.rs
+++ b/lib/components/fabro-tool/src/workflow_version.rs
@@ -21,8 +21,9 @@ pub struct FabroWorkflowVersionCreateParams {
     #[schemars(with = "String")]
     pub entrypoint: WorkflowPath,
     /// All local dependencies, keyed by package-relative path. Values are text
-    /// contents.
-    #[serde(deserialize_with = "fabro_types::deserialize_unique_map")]
+    /// contents. Tool arguments arrive as an already-parsed JSON value on
+    /// every production route, so duplicate keys have collapsed (last wins)
+    /// before this type sees them; there is no byte-level guard to add here.
     #[schemars(with = "BTreeMap<String, String>")]
     pub files:      BTreeMap<WorkflowPath, String>,
 }
@@ -127,12 +128,6 @@ mod tests {
     fn workflow_version_request_rejects_unknown_fields_and_invalid_paths() {
         let valid = json!({"entrypoint": "workflow", "files": {"workflow": "digraph W {}"}});
         validate(valid.clone()).unwrap();
-        assert!(
-            serde_json::from_str::<FabroWorkflowVersionCreateParams>(
-                r#"{"entrypoint":"workflow","files":{"workflow":"a","workflow":"b"}}"#
-            )
-            .is_err()
-        );
         for field in [
             "cwd",
             "url",
diff --git a/lib/foundation/fabro-types/src/lib.rs b/lib/foundation/fabro-types/src/lib.rs
index a398b827b..e678a8a1f 100644
--- a/lib/foundation/fabro-types/src/lib.rs
+++ b/lib/foundation/fabro-types/src/lib.rs
@@ -197,7 +197,7 @@ pub use workflow_path::{
 };
 pub use workflow_version::{
     MAX_WORKFLOW_VERSION_BYTES, MAX_WORKFLOW_VERSION_DEPENDENCIES, MAX_WORKFLOW_VERSION_FILE_BYTES,
-    MAX_WORKFLOW_VERSION_FILES, WorkflowVersion, WorkflowVersionShapeError, deserialize_unique_map,
+    MAX_WORKFLOW_VERSION_FILES, WorkflowVersion, WorkflowVersionShapeError,
     validate_workflow_source_paths,
 };
 pub use workflow_version_id::{WorkflowVersionId, WorkflowVersionIdParseError};
diff --git a/lib/foundation/fabro-types/src/workflow_version.rs b/lib/foundation/fabro-types/src/workflow_version.rs
index 297e485d6..a957f1b36 100644
--- a/lib/foundation/fabro-types/src/workflow_version.rs
+++ b/lib/foundation/fabro-types/src/workflow_version.rs
@@ -236,17 +236,6 @@ impl<'de> Deserialize<'de> for WorkflowVersion {
     }
 }
 
-/// Deserialize a map while rejecting duplicate keys, which serde would
-/// otherwise silently collapse to the last value.
-pub fn deserialize_unique_map<'de, D, K, V>(deserializer: D) -> Result<BTreeMap<K, V>, D::Error>
-where
-    D: Deserializer<'de>,
-    K: Deserialize<'de> + Ord + fmt::Display,
-    V: Deserialize<'de>,
-{
-    UniqueBTreeMap::deserialize(deserializer).map(|map| map.0)
-}
-
 struct UniqueBTreeMap<K, V>(BTreeMap<K, V>);
 
 impl<'de, K, V> Deserialize<'de> for UniqueBTreeMap<K, V>