Defensive payload parsing: absent, never zero

Status

Accepted — hardened in Phase 3 against the docs/swagger/ reference.

Context

BMC Redfish payloads are unreliable: string-typed numbers, per-vendor value shapes (the [{"Member": …}] form), "N/A" strings, and stray \r. The exporter already strips \r and uses tolerant types (xstring, asFloat64); a recent fix ensured xstring unmarshalling cannot panic. The family rule: an unparseable value yields an absent sample, never a zero — a fake 0 on a capacity or error metric silently corrupts dashboards and alerts.

Decision

Keep tolerant parsing localized (the unmarshal.go helpers). Custom UnmarshalJSON must never panic. When a field cannot be parsed, emit no sample for it rather than a zero. Validate the response structs in model.go against the Dell iDRAC 10 and DMTF Redfish OpenAPI documents in docs/swagger/ during the Phase 3 realignment pass.

Consequences

Missing/garbled fields disappear from /metrics instead of reporting misleading zeros. The OpenAPI specs are the authority for field names and shapes.