The experimental info() PromQL function returns no results when the info-selector filters by a label that already exists on the input vector, even when that label exists on target_info with a matching value.

Steps to Reproduce

Given OTLP metrics with resource attributes that result in:

Metric:
postgresql_commits_total{host_name="orbstack", instance="postgresql/postgres", job="postgresql"}

target_info:
target_info{host_name="orbstack", instance="postgresql/postgres", job="postgresql", service_name="postgresql", ...}

Note: host_name is promoted to the metric via promote_resource_attributes, so it exists on both the metric and target_info.

Queries and results:

Works - no filter

info(postgresql_commits_total)

✓ Returns enriched metrics

Works - filter by label only on target_info

info(postgresql_commits_total, {service_name="postgresql"})

✓ Returns enriched metrics

FAILS - filter by label that exists on BOTH metric and target_info

info(postgresql_commits_total, {host_name="orbstack"})

✗ Returns empty

info(postgresql_commits_total, {host_name=~".+"})

✗ Returns empty

Expected Behavior

All queries should return results. The info-selector filters which target_info series to consider. Since a matching target_info exists, the join should succeed regardless of whether the filter label also exists on the input metric.

Actual Behavior

When the info-selector includes a label that already exists on the input vector, info() returns no results.

Workaround

Filter on the metric directly, use info() selector only for labels exclusive to target_info:

info(postgresql_commits_total{host_name=~"$host_name"}, {service_name="postgresql"})