CLAUDE_CODE_OTEL_DIAG_STDERR was always set when OTEL is enabled, making
OTEL SDK errors (e.g. 404 from a misconfigured collector endpoint) appear
in every agent's stderr unconditionally. Move it behind a new opt-in flag.
Changes:
- nix/modules/hive-c0re.nix: add services.hyperhive.otel.debug (bool,
default false); wire to HYPERHIVE_OTEL_DEBUG env on hive-c0re unit.
- hive-c0re/src/meta.rs: add debug field to OtelConfig; read
HYPERHIVE_OTEL_DEBUG; emit hyperhive.otel.debug = true when set.
- nix/templates/harness-base.nix: add hyperhive.otel.debug internal
option; move CLAUDE_CODE_OTEL_DIAG_STDERR out of otelSettingsEnv into
a debug-gated lib.optionalAttrs block.
Default behaviour: OTEL exports silently (no stderr noise). Operators
troubleshooting collector connectivity set services.hyperhive.otel.debug
= true to re-enable the diagnostic output.
cb0a66147a