Function singleton_mapping_sequence 

pub fn singleton_mapping_sequence(m: Mapping) -> Value

Wrap a single serde_yaml::Mapping as the sole element of a serde_yaml::Value::Sequence, returning the ready-to-drop singleton-mapping-sequence Value.

The canonical shape every K8s-CRD schema-list-shape-required field with exactly one entry to emit lands the same Value::Sequence(vec![Value::Mapping(m)]) three-token block in front of. Seven identical-shape call sites across caixa-mesh collapse onto this helper:

• Cilium CiliumNetworkPolicy.spec.ingress[].toPorts[].ports (one port_entry per typed edge, wrapped in the CRD’s required-list-shape ports: axis);
• Cilium CiliumNetworkPolicy.spec.ingress[].toPorts[].rules.http (one http_rule per L7-introspection-capable crate::WitTarget::Http contract, wrapped in the CRD’s required-list-shape http: axis);
• Cilium CiliumNetworkPolicy.spec.ingress (one ingress_rule per policy — Cilium’s CRD schema lists the per-policy ingress ruleset even though V0 emits exactly one entry);
• Gateway API Gateway.spec.listeners (one listener per Gateway — V0 emits the single HTTP-listener shape the sibling GATEWAY_API_DEFAULT_HTTP_LISTENER_NAME + GATEWAY_API_DEFAULT_HTTP_LISTENER_PORT consts pin);
• Gateway API HTTPRoute.spec.rules[].matches (one match_entry per rule — V0 emits a single per-path prefix-match);
• Gateway API HTTPRoute.spec.rules[].backendRefs (one backend_ref per rule — V0 emits a single-backend fan-in on the :entrada :para destination Servico);
• Gateway API HTTPRoute.spec.parentRefs (one parent_ref per route — every route attaches to exactly one Gateway).

Until this lift landed all seven call sites re-inlined the same three-token boilerplate — serde_yaml:: path re-quote, Value::Sequence(_) promotion, vec![serde_yaml::Value::Mapping(_)] singleton-list wrapping — around a one-token semantic payload (the per-site Mapping). Lifting collapses the boilerplate into one function call the caller reads as intent (singleton_mapping_sequence (<mapping>) — “wrap this single mapping as the CRD-required list- shape”) rather than three hand-spelled positional artifacts. The next renderer to land — the per-:politicas CiliumClusterwideEnvoyConfig emitter (MESH-COMPOSITION §III.2 #3, which drops singleton resources:[] / listeners:[] / virtualHosts:[] blocks under its per-policy CR spec), the app-operator’s typed mesh.pleme.io/v1alpha1/Aplicacao CR materializer (§III.2 #5, whose spec.selectors:[] / spec.gates:[] blocks list-shape a single per-Aplicacao entry), the M4 cross- cluster fan-out’s per-cluster Service.spec.ports[] / HTTPRoute.spec.rules[].backendRefs[] emission, the future caixa-otel OpenTelemetry-Collector pipelines.traces.receivers[] / pipelines.traces.exporters[] singleton-list-shape emission — gets the canonical CRD-list-shape-wrap for free with one function call, instead of re-inlining the same three-token block. Peer with the sibling render-side helpers on the serde_yaml::Value- construction surface (yaml_string_mapping, label_selector, kube_resource_skeleton, single_field_overlay, the sibling MappingExt::insert_str_key primitive) — each closes a distinct axis of the K8s-artifact-emit surface’s “same shape, written N times” duplication.

The helper takes an owned serde_yaml::Mapping (moving into the wrapping vec! without a clone) because every call site has just finished building the mapping locally and passes it by value to the insert-under-outer-key step. A [Value::Mapping] wrapping of the same mapping is one step further along the emit trajectory — the helper closes the gap in one primitive.

The seven caixa-mesh call sites all followed the same insert-under-outer-key step, so the composition mapping.insert_str_key(K, singleton_mapping_sequence(m)) is itself lifted onto the sibling MappingExt::insert_singleton_mapping_sequence method — every caixa-mesh site now reaches for the composed method rather than nesting the two calls at the call site. This standalone helper remains the semantic primitive for the singleton-Mapping-list-shape Value (the trait method’s impl composes it internally), and stays public for future callers that want the raw Value::Sequence(vec![Value::Mapping(m)]) payload without inserting it under a schema key.