review #3: fix remaining Result generic-param duplicates and consolidate

The previous fix changed only the lowerer's builtin_generic_type_params; two more
identical copies (hir.rs, checks/calls.rs — the latter drives the actual generic
substitution) still mapped Result -> [K,V] instead of [T,E], weakening
Result.map/map_error/and_then substitution. Fixed both, then consolidated all three
into a single text_util::builtin_generic_type_params so the names can't drift per
layer again.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: Haofei

crates/rsscript/src/checks/calls.rs

@@ -4847,16 +4847,7 @@ pub(crate) fn unresolved_generic_type(type_name: &str) -> bool {
             .any(|param_type| unresolved_generic_type(param_type))
 }
 
-fn builtin_generic_type_params(root: &str) -> Option<Vec<&'static str>> {
-    match root {
-        "List" | "Set" | "Option" | "ResourcePool" | "Channel" | "Sender" | "Receiver"
-        | "Stream" | "Pipeline" => Some(vec!["T"]),
-        "FalliblePipeline" => Some(vec!["T", "E"]),
-        "Capability" => Some(vec!["P"]),
-        "Map" | "Result" => Some(vec!["K", "V"]),
-        _ => None,
-    }
-}
+use crate::text_util::builtin_generic_type_params;
 
 fn hir_expr_span(expr: &HirExpr) -> &Span {
     match expr {

crates/rsscript/src/hir.rs

@@ -2869,16 +2869,7 @@ fn substitute_type_params(type_name: &str, substitutions: &HashMap<String, Strin
     format!("{root}<{args}>")
 }
 
-fn builtin_generic_type_params(root: &str) -> Option<Vec<&'static str>> {
-    match root {
-        "List" | "Set" | "Option" | "ResourcePool" | "Channel" | "Sender" | "Receiver"
-        | "Stream" | "Pipeline" => Some(vec!["T"]),
-        "FalliblePipeline" => Some(vec!["T", "E"]),
-        "Capability" => Some(vec!["P"]),
-        "Map" | "Result" => Some(vec!["K", "V"]),
-        _ => None,
-    }
-}
+use crate::text_util::builtin_generic_type_params;
 
 fn capability_protocol(type_name: &str) -> Option<&str> {
     let root = type_root_name(type_name);

crates/rsscript/src/rust_lower/lowerer.rs

@@ -5450,17 +5450,7 @@ fn collect_type_ref_substitutions(
     }
 }
 
-fn builtin_generic_type_params(root: &str) -> Option<Vec<&'static str>> {
-    match root {
-        "List" | "Set" | "Option" | "ResourcePool" | "Channel" | "Sender" | "Receiver"
-        | "Stream" | "Pipeline" => Some(vec!["T"]),
-        "FalliblePipeline" => Some(vec!["T", "E"]),
-        "Capability" => Some(vec!["P"]),
-        "Map" => Some(vec!["K", "V"]),
-        "Result" => Some(vec!["T", "E"]),
-        _ => None,
-    }
-}
+use crate::text_util::builtin_generic_type_params;
 
 /// Type names declared by the bundled stdlib (`builtin`) interfaces. These are
 /// runtime-backed (lowered as `rsscript_runtime::X`), so they must be kept out of

crates/rsscript/src/text_util.rs

@@ -146,3 +146,21 @@ pub(crate) fn split_top_level_type_args(args: &str) -> Vec<&str> {
     }
     parts
 }
+
+/// Declared generic parameter names for a builtin generic type root, e.g.
+/// `Map<K, V>` -> `["K", "V"]`, `Result<T, E>` -> `["T", "E"]`, `List<T>` ->
+/// `["T"]`. `None` for non-generic / unknown roots. Single source of truth: the
+/// HIR substitution path, the call-site substitution path, and the Rust lowerer
+/// all use this, so the names can't drift apart per layer (they did once: a
+/// `Result -> ["K","V"]` copy weakened error-combinator substitution).
+pub(crate) fn builtin_generic_type_params(root: &str) -> Option<Vec<&'static str>> {
+    match root {
+        "List" | "Set" | "Option" | "ResourcePool" | "Channel" | "Sender" | "Receiver"
+        | "Stream" | "Pipeline" => Some(vec!["T"]),
+        "FalliblePipeline" => Some(vec!["T", "E"]),
+        "Capability" => Some(vec!["P"]),
+        "Map" => Some(vec!["K", "V"]),
+        "Result" => Some(vec!["T", "E"]),
+        _ => None,
+    }
+}