Constant M3_PLACEMENT_KEY_AFFINITY 

pub const M3_PLACEMENT_KEY_AFFINITY: &str = "affinity";

Canonical camelCase YAML sub-key for the crate::aplicacao::Placement struct’s affinity placement-engine-hint axis — the per-M3_KEY_PLACEMENT- block optional field carrying the validated non-empty affinity hint (per crate::aplicacao::AplicacaoSpec::validate_placement) that every downstream placement-hint consumer weights off:

• the lareira-fleet-programs aggregator’s per-entry M3 Adaptive compression pass reading placement.affinity to weight the emitted ComputeUnit’s replica-distribution overlay per MESH-COMPOSITION.md §V,
• the future app-operator reconciler’s per-Aplicacao pod-affinity / node-affinity K8s-primitive materializer keying off the same value as an app.pleme.io/affinity-hint=<value> label selector,
• the future mesh.pleme.io/v1alpha1/Aplicacao CR materializer’s admission-time spec.placement.affinity typed-string bind, and
• the M4 cross-cluster placement engine’s per-hint takeover-priority dispatch on the same value (data-locality / low-latency / anti-affinity per the [crate::aplicacao::validate_placement_affinity] value-shape gate’s documented canonical hint set).

The scalar is derived by crate::aplicacao::Placement’s #[serde(rename_all = "camelCase")] from the Rust field name affinity; affinity has no _, so the serde transform is a no-op on this axis and the emitted key equals the source-side field name byte-for-byte. Unlike the always-emitted M3_PLACEMENT_KEY_ESTRATEGIA / M3_PLACEMENT_KEY_CLUSTERS axes, the affinity field carries a #[serde(skip_serializing_if = "Option::is_none")] attribute so the key appears in the rendered placement: block iff the typed slot resolves to Some(_) — the omit-when-unset contract the peer typed slots (crate::aplicacao::MeshPolicy::timeout, crate::aplicacao::MeshPolicy::retries, crate::aplicacao::MeshPolicy::mtls_required) each carry to keep an unset typed slot from bloating every rendered programs.yaml entry with a nominal-only affinity: null value the downstream weighting passes would then need to unwrap defensively.

Lifting the byte to one &'static str closes the same drift footgun the peer M3_PLACEMENT_KEY_ESTRATEGIA / M3_PLACEMENT_KEY_CLUSTERS lifts closed on the sibling always-emitted axes: a future refactor renaming the Rust field (affinity → affinityHint for schema-clarity, placementHint for symmetry with the future per-cluster affinity hierarchy, etc.) OR retaining the field name while adding a #[serde(rename = "…")] override would silently emit a placement: block whose affinity hint lands under one key while every downstream weighting consumer still probes another — the M3 Adaptive compression pass would then see a None affinity on every entry and silently fall back to the uniform-weight baseline (the workload’s typed :affinity "data-locality" hint would be silently discarded, and the failure surfaces as “the newly-deployed Aplicacao’s replicas don’t cluster where the typed slot said they should” far from the rebrand commit’s source). The identity pin + serde-derive round-trip pin the sweep introduces catch the drift at caixa-core / caixa-mesh build time rather than at the aggregator’s weighting step or the operator’s reconcile posture.

Peer of M3_KEY_PLACEMENT / M3_PLACEMENT_KEY_ESTRATEGIA / M3_PLACEMENT_KEY_CLUSTERS on the same programs.yaml per-entry axis — M3_KEY_PLACEMENT names the top-level overlay key each entry carries, M3_PLACEMENT_KEY_ESTRATEGIA names the per-sub-block distribution-strategy discriminator every dispatch consumer branches on, M3_PLACEMENT_KEY_CLUSTERS names the per-sub-block cluster-pool list every per-cluster fanout consumer scopes by, this constant names the per-sub-block optional placement-engine hint every weighting consumer reads off.