fix(adapters): hoist path-template validation into shared forward core, run at from_openapi import (JS-02)

Import-time path-template checks now run on both adapters:
- from_jsonschema: validate_path_template moves to forward.rs (same
  checks, same messages, shared implementation)
- from_openapi: build_registration calls it before building each op, so
  a template like /x{open fails import with 'unterminated placeholder'
  instead of a per-call INTERNAL on first invoke
- new test: unterminated_path_template_fails_import_not_first_call

src/adapters/forward.rs

@@ -122,6 +122,7 @@
 use std::collections::HashMap;
 use std::sync::Arc;
 
+use alkcall::client::AdapterError;
 use alkcall::protocol::wire::{CallError, ResponseEnvelope};
 use alkcall::registry::context::OperationContext;
 use alkcall::registry::registration::ResponseStream;
@@ -176,6 +177,35 @@ pub(crate) const GATEWAY_BODY_KEY: &str = "body";
 pub(crate) const HEADER_PARAM_IN_MARKER: &str = "wire";
 pub(crate) const HEADER_PARAM_MARKER_VALUE: &str = "header";
 
+/// Import-time path-template validation shared by `from_jsonschema`
+/// (review 001 OAI-09) and `from_openapi` (review 002 JS-02): every
+/// `{placeholder}` must terminate with a `}` and carry a name. A
+/// template that slips through (e.g. `/x{open`) otherwise surfaces as a
+/// per-call `INTERNAL` error on first invoke — the eager-validation
+/// promise both adapters make.
+pub(crate) fn validate_path_template(path_template: &str) -> Result<(), AdapterError> {
+    let mut rest = path_template;
+    while let Some(start) = rest.find('{') {
+        let Some(end_rel) = rest[start..].find('}') else {
+            return Err(AdapterError::SchemaParse {
+                message: format!("path template `{path_template}` has an unterminated placeholder"),
+            });
+        };
+        if rest[start + 1..start + end_rel].is_empty() {
+            return Err(AdapterError::SchemaParse {
+                message: format!("path template `{path_template}` has an empty placeholder name"),
+            });
+        }
+        rest = &rest[start + end_rel + 1..];
+    }
+    if path_template.contains('}') && !path_template.contains('{') {
+        return Err(AdapterError::SchemaParse {
+            message: format!("path template `{path_template}` has `}}` without a matching `{{`"),
+        });
+    }
+    Ok(())
+}
+
 /// The credential scheme forwarded handlers apply to outbound requests
 /// (ADR-014). The credential value itself flows through
 /// `OperationContext.capabilities` at call time — never through this

src/adapters/from_jsonschema.rs

@@ -32,7 +32,7 @@ use async_trait::async_trait;
 use reqwest::Method;
 use serde_json::Value;
 
-use super::forward::{forward, forward_stream, HttpServiceConfig};
+use super::forward::{forward, forward_stream, validate_path_template, HttpServiceConfig};
 use crate::client::SharedHttpClient;
 
 /// The HTTP-backed single-endpoint adapter (ADR-066): one caller-built
@@ -139,30 +139,6 @@ fn validate_method(method: &str) -> Result<(), AdapterError> {
     })?;
     Ok(())
 }
-
-fn validate_path_template(path_template: &str) -> Result<(), AdapterError> {
-    let mut rest = path_template;
-    while let Some(start) = rest.find('{') {
-        let Some(end_rel) = rest[start..].find('}') else {
-            return Err(AdapterError::SchemaParse {
-                message: format!("path template `{path_template}` has an unterminated placeholder"),
-            });
-        };
-        if rest[start + 1..start + end_rel].is_empty() {
-            return Err(AdapterError::SchemaParse {
-                message: format!("path template `{path_template}` has an empty placeholder name"),
-            });
-        }
-        rest = &rest[start + end_rel + 1..];
-    }
-    if path_template.contains('}') && !path_template.contains('{') {
-        return Err(AdapterError::SchemaParse {
-            message: format!("path template `{path_template}` has `}}` without a matching `{{`"),
-        });
-    }
-    Ok(())
-}
-
 fn spec_name_references_undeclared(spec: &OperationSpec, path_template: &str) -> bool {
     let properties = spec
         .input_schema

src/adapters/from_openapi.rs

@@ -27,8 +27,8 @@ use async_trait::async_trait;
 use serde_json::Value;
 
 use super::forward::{
-    forward, forward_stream, HttpServiceConfig, GATEWAY_BODY_KEY, HEADER_PARAM_IN_MARKER,
-    HEADER_PARAM_MARKER_VALUE,
+    forward, forward_stream, validate_path_template, HttpServiceConfig, GATEWAY_BODY_KEY,
+    HEADER_PARAM_IN_MARKER, HEADER_PARAM_MARKER_VALUE,
 };
 use super::openapi_spec::{OpenAPISpec, Operation, Parameter, SUCCESS_RESPONSE_KEYS};
 use crate::client::SharedHttpClient;
@@ -310,6 +310,7 @@ impl FromOpenAPI {
         op: &Operation,
         path_parameters: &[Parameter],
     ) -> Result<HandlerRegistration, AdapterError> {
+        validate_path_template(path)?;
         let name = Self::normalize_operation_id(op, method, path);
         let qualified_name = format!("{}/{name}", self.config.namespace);
         let op_type = Self::detect_op_type(method, op);
@@ -810,6 +811,32 @@ mod tests {
         }
     }
 
+    #[tokio::test]
+    async fn unterminated_path_template_fails_import_not_first_call() {
+        let doc = r#"{
+            "openapi":"3.0.0","info":{"title":"T","version":"1"},
+            "paths":{"/x{open":{"get":{"operationId":"x","responses":{"200":{"content":{"application/json":{"schema":{}}}}}}}}
+        }"#;
+        let spec = OpenAPISpec::from_json(doc).unwrap();
+        let result = adapter(spec, config("ns", "https://x", None))
+            .import()
+            .await;
+        match result {
+            Err(AdapterError::SchemaParse { message }) => {
+                assert!(
+                    message.contains("unterminated placeholder"),
+                    "message was: {message}"
+                );
+                assert!(message.contains("/x{open"), "message was: {message}");
+            }
+            Ok(bundles) => panic!(
+                "unterminated path template must fail at import (JS-02), got {} bundles",
+                bundles.len()
+            ),
+            Err(e) => panic!("expected SchemaParse, got {e}"),
+        }
+    }
+
     #[tokio::test]
     async fn op_type_detection() {
         let get_doc = r#"{"openapi":"3.0.0","info":{"title":"T","version":"1"},"paths":{"/g":{"get":{"operationId":"g","responses":{"200":{"content":{"application/json":{"schema":{}}}}}}}}}"#;