Function kube_field_map 

pub fn kube_field_map<'a, R: KubeReceiver + ?Sized>(
    recv: &'a R,
    field: &str,
    map_field: &str,
) -> Option<&'a Mapping>

Read a sub-<mid>.<tail> YAML sub-mapping nested two hops under an arbitrary KubeReceiver as Option<&serde_yaml::Mapping> — the value-level three-hop navigation primitive that folds .get(<mid>) .and_then(|v| v.get(<tail>)).and_then(|v| v.as_mapping()) into a single helper call. Exactly kube_field(recv, mid).and_then(|v| kube_map(v, tail)) — the composed peer of the value-level kube_field (e04c234) one-hop pass-through and the value-level sub-mapping-arity kube_map (28fa5d8) two-hop accessor. Sub- mapping-arity sibling of the composed scalar-str kube_field_str (1c68424), composed scalar-u64 kube_field_u64 (e6fca52), composed scalar-bool kube_field_bool (261894b), composed sequence-tail kube_field_seq (a45bd8b), and composed raw-tail kube_field_field (cb5d862) accessors on the same three-hop axis: where those five composed accessors fold a trailing .as_str() / .as_u64() / .as_bool() / .as_sequence() shape- gate (or pass through the raw &Value tail) onto the two-hop- nested navigation, this accessor folds the trailing .as_mapping() shape-gate on the same navigation, so every routed two-hop .and_then(|X| kube_field(X, <MID>)).and_then(|Y| kube_map(Y, <TAIL>)) middle-hop-plus-sub-mapping-tail block (the canonical per-K8s-document metadata.labels per-resource-label-block readback on the KUBE_KEY_METADATA middle-hop + KUBE_KEY_LABELS tail axis the sibling specialization kube_metadata_labels already pins from the root, the future per-HTTPRoute per-rule matches[<i>].path per-match path-selection sub-mapping readback once the M4 typed per-match overlay lands, the future per-CNP spec.egress[<i>].authentication per-egress auth sub-mapping readback under an egress-authentication overlay, the future per- HelmRelease per-spec.values.<library> per-child-chart sub- mapping readback once the [&Mapping]-receiver overlay peer lands) folds onto one dispatch.

Returns None on any of the four short-circuit arms folded through the underlying three-hop composition: the receiver carries a YAML type without a get(<mid>) navigation surface (serde_yaml::Value::get returns None on scalar arms — string, bool, number, null — that expose no per-key lookup), the requested <mid> middle-hop axis-key is absent from the receiver’s mapping, the <mid> sub-field value is present but carries a YAML shape with no get(<tail>) navigation surface (a scalar arm at the middle-hop altitude — the inner serde_yaml::Value::get scalar- arm None folds through), or the <tail> value is present but carries a non-mapping YAML type (the trailing .as_mapping() shape-gate short-circuit — a schema-invalid nested type per the K8s apiserver’s OpenAPI schema but tolerated here as None so the readback stays a total function, mirroring the sibling kube_field_str / kube_field_u64 / kube_field_bool / kube_field_seq posture). The returned &Mapping borrows into the input receiver — the caller decides whether to .iter() for a per-key enumeration, .contains_key(<K>) for a presence probe, .get(<K>) for a downstream .and_then continuation, or .expect(...) for a load-bearing full-sub-mapping bind.

Closes the composed value-level shape-gated family at the fifth and final of the shape-gate arities the four sibling shape-gated composed accessors opened — with this sub-mapping-arity peer the family now spans str, u64, bool, sequence, and sub-mapping at the two-hop-nested altitude, matching the closed shape of the spec- anchored family one altitude above where kube_spec_field plus the shape-gated kube_spec_str_field / kube_spec_u64_field / kube_spec_bool_field / kube_spec_seq_field / kube_spec_map_field variants already span the axis, and the closed shape of the value-level primitive family (kube_field, kube_str, kube_u64, kube_bool, kube_seq, kube_map) one altitude below where the value-level primitives already span the K8s apiserver OpenAPI schema shape arities the two-hop navigation resolves through. The routed producer-side specialization kube_metadata_labels on the canonical metadata.labels per-K8s-document axis (already lifted) is the natural composition-symmetric peer at the M2/M3 metadata altitude that this generic composed accessor closes at the composed value- level altitude.

Every future nested <mid>.<tail> sub-mapping readback the M3.x + M4 renderer set materializes (the future per-:contratos per-edge WIT-attribute nested sub-mapping once the M4 typed per-edge overlay lands, the future per-Aplicacao spec.placement.affinity.podAffinity nested pod-affinity sub- mapping readback under a placement-shape probe, the future caixa-otel per-Servico per-processors.<name>.config nested processor-config sub-mapping probe, every future test-side nested- sub-mapping readback the M3.x + M4 renderer set adds under .contains_key(<K>) / .iter() / .get(<K>).and_then(...) enumeration) reaches this one helper by construction. No per- consumer two-hop re-inline; no coordinated rewrite across every nested-sub-mapping readback on a future serde_yaml surface rebrand or shape-gate shift. Symmetric closure of the composed value-level shape-gated family the four prior lifts opened.