diff --git a/src/client.jl b/src/client.jl
index 583c611..b310e16 100644
--- a/src/client.jl
+++ b/src/client.jl
@@ -1070,14 +1070,19 @@ function _header_descriptor(header::NormalizedHeader, type::String)
            ", content = " * content * ")"
 end
 
-function _security_descriptor(requirements)
+function _security_descriptor(requirements, known_schemes)
     Base.@nospecialize requirements
     alternatives = String[]
     for requirement in requirements
+        # Permissive normalization keeps requirements naming schemes declared
+        # outside this document (warned as :unknown_security_scheme). The
+        # runtime cannot construct credentials for a scheme it cannot see, so
+        # exclude them; a group left empty is an anonymous alternative and the
+        # caller supplies external auth explicitly.
         entries = String[
             "(name = " * repr(name) *
             ", scopes = " * _julia_literal(scopes) * ")" for
-            (name, scopes) in requirement.alternatives
+            (name, scopes) in requirement.alternatives if name in known_schemes
         ]
         push!(alternatives, "(" * join(entries, ',') * (length(entries) == 1 ? "," : "") * ")")
     end
@@ -1131,7 +1136,8 @@ function _emit_operation_descriptor(io, operation::OperationPlan, api::Normalize
         )
     end
     println(io, "    ),")
-    println(io, "    security = ", _security_descriptor(operation.operation.security), ",")
+    known_schemes = Set{String}(scheme.name for scheme in api.security_schemes)
+    println(io, "    security = ", _security_descriptor(operation.operation.security, known_schemes), ",")
     println(
         io,
         "    servers = ",
diff --git a/src/normalize.jl b/src/normalize.jl
index ea38921..3a17341 100644
--- a/src/normalize.jl
+++ b/src/normalize.jl
@@ -1748,12 +1748,32 @@ function _validate_security_references!(context, requirements, schemes)
                 end
             end
             scheme === nothing && begin
-                _reference_error!(
-                    context.resolver,
-                    :unknown_security_scheme,
-                    "security requirement refers to unknown scheme $(repr(name))",
-                    requirement.provenance.node,
-                )
+                # Strict mode enforces the Security Requirement Object's MUST
+                # (the name corresponds to a declared scheme). Permissive mode
+                # supports the specification's multi-document pattern, where a
+                # referenced document names schemes its entry document
+                # declares: the scheme is treated as externally declared, and
+                # generation excludes it from credential enforcement.
+                if context.resolver.strict
+                    _reference_error!(
+                        context.resolver,
+                        :unknown_security_scheme,
+                        "security requirement refers to unknown scheme $(repr(name))",
+                        requirement.provenance.node,
+                    )
+                else
+                    _warning!(
+                        context.resolver.bag,
+                        :unknown_security_scheme,
+                        "security requirement refers to unknown scheme $(repr(name)); " *
+                        "treating it as externally declared and excluding it from " *
+                        "generated credential enforcement",
+                        SourceLocation(
+                            requirement.provenance.node.resource,
+                            requirement.provenance.node.pointer,
+                        ),
+                    )
+                end
                 continue
             end
             if version.minor < 2 &&
diff --git a/src/planning.jl b/src/planning.jl
index dcf9dc1..2e3ff39 100644
--- a/src/planning.jl
+++ b/src/planning.jl
@@ -1682,6 +1682,27 @@ end
 function _check_server_generation_support!(context::PlanningContext, strict::Bool)
     for operation in context.api.operations
         operation.direction === :request || continue
+        # The OAS Responses Object SHOULD cover a successful operation
+        # response; documents regularly violate that (petstore's addPet lists
+        # only 405). Handlers of such operations answer `nothing` with an
+        # empty 200 at runtime — surface that here instead of per-request.
+        if !any(operation.responses) do response
+            selector = uppercase(response.selector)
+            (!isempty(selector) && all(isdigit, selector) && startswith(selector, '2')) ||
+                selector == "2XX" || selector == "DEFAULT"
+        end
+            _warning!(
+                context.bag,
+                :missing_success_response,
+                "operation $(repr(operation.id)) documents no success response; " *
+                "handlers returning `nothing` are answered with an empty 200, " *
+                "and any other response needs an explicit framework response",
+                SourceLocation(
+                    operation.provenance.node.resource,
+                    operation.provenance.node.pointer,
+                ),
+            )
+        end
         # A form-style exploded object query or cookie parameter consumes
         # arbitrary wire names. One such parameter per location decodes from the
         # pairs no other declared parameter claimed; two or more are ambiguous.
diff --git a/src/runtime.jl b/src/runtime.jl
index 844d4bb..3e17689 100644
--- a/src/runtime.jl
+++ b/src/runtime.jl
@@ -1553,15 +1553,32 @@ function _decode_body(client::Client, type, content_type, body, schema)
             )
         return _decode(type, value, client.validate_responses)
     elseif _is_sequential_json_media(media)
+        # Sequential media is documented either with an array schema covering
+        # the whole sequence (planned as a vector type) or with the schema of
+        # one record (planned as the item type); mirror _stream_plan and
+        # support both.
         value = _decode_sequential_json(body, media)
-        client.validate_responses &&
-            _validate_schema(client.spec, 
-                schema,
-                value,
-                "decoding a sequential JSON response";
-                direction = :output,
-            )
-        return _decode(type, value, client.validate_responses)
+        if type <: AbstractVector && type !== Vector{UInt8}
+            client.validate_responses &&
+                _validate_schema(client.spec,
+                    schema,
+                    value,
+                    "decoding a sequential JSON response";
+                    direction = :output,
+                )
+            return _decode(type, value, client.validate_responses)
+        end
+        if client.validate_responses
+            for item in value
+                _validate_schema(client.spec,
+                    schema,
+                    item,
+                    "decoding a sequential JSON response";
+                    direction = :output,
+                )
+            end
+        end
+        return [_decode(type, item, client.validate_responses) for item in value]
     elseif startswith(media, "text/") || type === String
         isvalid(String, body) || throw(DecodeError("response text is not UTF-8"))
         value = String(copy(body))
diff --git a/src/servergen.jl b/src/servergen.jl
index d60717e..c9c5227 100644
--- a/src/servergen.jl
+++ b/src/servergen.jl
@@ -129,8 +129,12 @@ function _object_from_alternating(tokens, context; decode::Bool = false)
 end
 
 function _finish_parameter(descriptor, value, context)
-    _validate_schema(_SPEC, descriptor.schema, _encode(value), context; direction = :input)
-    return _decode(descriptor.type, value)
+    # _typed_scalar/_typed_array already construct generated value types (via
+    # _header_scalar), so decode from the encoded wire form: decoding the typed
+    # value itself would validate a Julia struct against its raw JSON schema.
+    encoded = _encode(value)
+    _validate_schema(_SPEC, descriptor.schema, encoded, context; direction = :input)
+    return _decode(descriptor.type, encoded)
 end
 
 function _decode_parameter_content(descriptor, text, context)
@@ -696,11 +700,18 @@ end
 
 function _server_response(operation, result)
     descriptor = _success_response(operation.responses)
-    descriptor === nothing && throw(ArgumentError(string(
-        "operation ",
-        operation.id,
-        " documents no success response",
-    )))
+    if descriptor === nothing
+        # The OAS Responses Object is non-exhaustive documentation, and some
+        # documents cover only error codes (flagged at planning time as
+        # :missing_success_response). Answer `nothing` with an empty 200; a
+        # typed value has no documented media to encode against.
+        result === nothing && return (200, Pair{String,String}[], UInt8[])
+        throw(ArgumentError(string(
+            "operation ",
+            operation.id,
+            " documents no success response; return `nothing` for an empty 200 or a framework response",
+        )))
+    end
     status = _selector_status(descriptor.selector)
     if isempty(descriptor.media)
         result === nothing || throw(ArgumentError(string(
@@ -735,8 +746,22 @@ function _server_response(operation, result)
         _validate_schema(_SPEC, entry.schema, lowered, context; direction = :output)
         payload = Vector{UInt8}(codeunits(JSON.json(lowered)))
     elseif _is_sequential_json_media(media)
+        # Sequential media is documented either with an array schema covering
+        # the whole sequence (planned as a vector type) or with the schema of
+        # one record (planned as the item type); validate accordingly.
         lowered = _encode(result)
-        _validate_schema(_SPEC, entry.schema, lowered, context; direction = :output)
+        lowered isa AbstractVector || lowered isa Tuple || throw(ArgumentError(string(
+            "operation ",
+            operation.id,
+            " documents a sequential JSON response; return an array or tuple of items",
+        )))
+        if entry.type <: AbstractVector && entry.type !== Vector{UInt8}
+            _validate_schema(_SPEC, entry.schema, lowered, context; direction = :output)
+        else
+            for item in lowered
+                _validate_schema(_SPEC, entry.schema, item, context; direction = :output)
+            end
+        end
         payload = Vector{UInt8}(codeunits(_encode_sequential_json(result, media)))
     elseif startswith(media, "text/")
         result isa AbstractString || throw(ArgumentError(string(
diff --git a/test/semantics.jl b/test/semantics.jl
index 19e642f..ab532a6 100644
--- a/test/semantics.jl
+++ b/test/semantics.jl
@@ -470,4 +470,68 @@ end
         @test :unknown_oauth_scope in codes
         @test :duplicate_server_name in codes
     end
+
+    @testset "externally declared security schemes" begin
+        # The Security Requirement Object's names MUST correspond to declared
+        # schemes, but the specification's multi-document pattern lets a
+        # referenced document name schemes its entry document declares. Strict
+        # mode enforces the MUST; permissive mode warns and generation excludes
+        # the unknown scheme from credential enforcement.
+        document = minimal_openapi(
+            "3.0.3",
+            OpenAPI.obj(
+                "/things" => OpenAPI.obj(
+                    "get" => semantic_operation(
+                        "listThings";
+                        responses = OpenAPI.obj(
+                            "200" => OpenAPI.obj(
+                                "description" => "ok",
+                                "content" => OpenAPI.obj(
+                                    "application/json" => OpenAPI.obj(
+                                        "schema" => OpenAPI.obj("type" => "string"),
+                                    ),
+                                ),
+                            ),
+                        ),
+                        security = Any[
+                            OpenAPI.obj("gatewayAuth" => Any[]),
+                            OpenAPI.obj("localKey" => Any[]),
+                        ],
+                    ),
+                ),
+            ),
+        )
+        document["components"] = OpenAPI.obj(
+            "securitySchemes" => OpenAPI.obj(
+                "localKey" => OpenAPI.obj(
+                    "type" => "apiKey",
+                    "name" => "X-Key",
+                    "in" => "header",
+                ),
+            ),
+        )
+
+        strict_error = @test_throws OpenAPI.OpenAPIError OpenAPI.normalize(document)
+        @test any(
+            diagnostic -> diagnostic.code === :unknown_security_scheme,
+            strict_error.value.diagnostics,
+        )
+
+        permissive = OpenAPI.normalize(document; strict = false)
+        warning = only(
+            diagnostic for diagnostic in permissive.diagnostics if
+            diagnostic.code === :unknown_security_scheme
+        )
+        @test warning.severity === :warning
+
+        # the unknown scheme is excluded from the generated operation security:
+        # its alternative becomes anonymous, and the declared scheme survives
+        source = OpenAPI.client(permissive; name = "ExternalAuthClient", strict = false)
+        @test occursin("security = ((),((name = \"localKey\", scopes = ()),)),", source)
+        # the unknown scheme survives only inside the embedded raw document,
+        # never as an enforceable descriptor or scheme entry
+        @test !occursin("name = \"gatewayAuth\"", source)
+        @test !occursin("\"gatewayAuth\" =>", source)
+        @test occursin("\"localKey\" => (type = :apikey", source)
+    end
 end