apc: expose NMC3 ambient temperature

[user01010111]

Summary

Fixes #3250.

APC Network Management Card 3 units expose universal I/O temperature through uioSensorStatusTemperatureDegC, but the APC subdriver does not currently map that value to ambient.temperature.

This adds the Universal I/O Celsius OID as the first ambient-temperature provider, rejects the MIB-defined -1 invalid sentinel, bumps APCC_MIB_VERSION to 1.62, and documents the addition in NEWS.adoc.

Schneider Electric's official PowerNet MIB v4.6.0, dated 9 July 2026, independently confirms the exact Celsius OID and the -1 invalid sentinel. Placing the new mapping before the existing Measure-UPS and IEM alternatives lets NMC3 devices use it when legacy OIDs are unavailable while preserving the current later-provider precedence on devices which answer those legacy OIDs.

Validation

• GCC 16.2.1 hard warnings with -Werror: clean complete snmp-ups compile and link passed.
• Clang 22 medium warnings with -Weverything -Werror: clean complete snmp-ups compile and link passed.
• The changed APC object passed Clang hard warnings with -Weverything -Werror.
• A compiled lookup-table check confirmed APC MIB version 1.62, the exact OID, scale 1, SU_FLAG_OK | SU_FLAG_NEGINVALID, and first-provider placement.
• The configured test suite passed 9/9 with loopback sockets available.
• make stylecheck, non-ASCII checks and git diff --check passed.
• make SPELLCHECK_ERROR_FATAL=no distcheck-light passed, including archive, build, check, install and uninstall.
• Spellcheck reported only existing findings in unchanged text; this change introduced none.
• Physical NMC3 confirmation remains pending.
• Upstream CI remains pending.

The whole-driver Clang hard profile stops on nine existing conversion warnings in unchanged snmp-ups.c. The changed APC object passes that profile, and the complete driver passes the project's medium Clang profile with -Werror.

General C checklist

• The change is one cohesive update to an existing subdriver.
• APCC_MIB_VERSION was bumped.
• The mapping uses the established ambient.temperature variable.
• The MIB-defined invalid value is rejected.
• Coding style, ASCII portability and distribution checks passed.
• NEWS.adoc was updated.

AI assistance

OpenAI Codex gpt-5.6-sol was used for planning, repository analysis, implementation, review, drafting and validation, including controller and delegated work. The human contributor reviewed the change and remains responsible for it.

[github-actions]

A ZIP file with standard source tarball and another tarball with pre-built docs for commit d0b0293 is temporarily available: NUT-tarballs-PR-3605.zip.

[AppVeyorBot]

✅ Build nut 2.8.5.5173-master completed (commit bfb14d4b41 by @)

• artifacts
• A 7-zip archive with built NUT for Windows debug binaries is temporarily available: NUT-for-Windows-x86_64-SNAPSHOT-2.8.5.5173-master.7z