Return -32602 for resource not found (SEP-2164) (#2920)

tests/interaction/_requirements.py

@@ -1142,8 +1142,10 @@ REQUIREMENTS: dict[str, Requirement] = {
     ),
     "mcpserver:resource:read-throws-surfaced": Requirement(
         source="sdk",
-        behavior="A resource function that raises is surfaced to the caller as a JSON-RPC error response.",
-        arm_exclusions=(ArmExclusion(reason="modern-error-surface", spec_version="2026-07-28"),),
+        behavior=(
+            "A resource function that raises is surfaced to the caller as a JSON-RPC error response "
+            "(-32603 Internal error), with the original exception text withheld."
+        ),
     ),
     "mcpserver:resource:static": Requirement(
         source="sdk",
@@ -1161,14 +1163,10 @@ REQUIREMENTS: dict[str, Requirement] = {
     ),
     "mcpserver:resource:unknown-uri": Requirement(
         source=f"{SPEC_BASE_URL}/server/resources#error-handling",
-        behavior="resources/read for a URI matching no registered resource returns JSON-RPC error -32002.",
-        divergence=Divergence(
-            note=(
-                "The spec reserves -32002 for resource-not-found; MCPServer raises ResourceError, which "
-                "the low-level server converts to error code 0."
-            ),
+        behavior=(
+            "resources/read for a URI matching no registered resource returns JSON-RPC error -32602 "
+            "(invalid params) with the requested URI in error.data, per SEP-2164."
         ),
-        arm_exclusions=(ArmExclusion(reason="modern-error-surface", spec_version="2026-07-28"),),
     ),
     # ═══════════════════════════════════════════════════════════════════════════
     # Prompts

tests/interaction/mcpserver/test_resources.py

@@ -112,10 +112,7 @@ async def test_read_templated_resource(connect: Connect) -> None:
 
 @requirement("mcpserver:resource:unknown-uri")
 async def test_read_unknown_uri_is_error(connect: Connect) -> None:
-    """Reading a URI that matches no registered resource fails with a JSON-RPC error.
-
-    The spec reserves -32002 for resource-not-found; see the divergence note on the requirement.
-    """
+    """Reading a URI that matches no registered resource fails with -32602 and the URI in data (SEP-2164)."""
     mcp = MCPServer("library")
 
     @mcp.resource("config://app")
@@ -127,16 +124,17 @@ async def test_read_unknown_uri_is_error(connect: Connect) -> None:
         with pytest.raises(MCPError) as exc_info:
             await client.read_resource("config://missing")
 
-    assert exc_info.value.error == snapshot(ErrorData(code=0, message="Unknown resource: config://missing"))
+    assert exc_info.value.error == snapshot(
+        ErrorData(code=-32602, message="Unknown resource: config://missing", data={"uri": "config://missing"})
+    )
 
 
 @requirement("mcpserver:resource:read-throws-surfaced")
 async def test_resource_function_that_raises_is_surfaced_as_a_jsonrpc_error(connect: Connect) -> None:
     """An exception raised by a resource function reaches the caller as a JSON-RPC error.
 
-    MCPServer wraps the failure in a generic error that names only the URI, so the original
-    exception text is not leaked to the client. The wrapped exception becomes error code 0 the
-    same way every other unhandled server-side exception does.
+    MCPServer wraps the failure in a generic ResourceError that names only the URI, so the original
+    exception text is not leaked to the client. The wrapped exception surfaces as -32603 Internal error.
     """
     mcp = MCPServer("library")
 
@@ -148,7 +146,9 @@ async def test_resource_function_that_raises_is_surfaced_as_a_jsonrpc_error(conn
         with pytest.raises(MCPError) as exc_info:
             await client.read_resource("res://boom")
 
-    assert exc_info.value.error == snapshot(ErrorData(code=0, message="Error reading resource res://boom"))
+    assert exc_info.value.error == snapshot(
+        ErrorData(code=-32603, message="Error reading resource res://boom", data={"uri": "res://boom"})
+    )
 
 
 @requirement("mcpserver:resource:duplicate-name")