Docker container labels with '/' in the key break Prometheus exposition parsing entirely #439

Description

When running scaphandre with --containers enabled, Docker container labels are exposed as Prometheus labels named container_label_<sanitized-key>. The key sanitization in ProcessTracker (src/sensors/utils.rs) escapes -, ., : and by replacing them with _, but does not escape /.

Container labels using Kubernetes/OCI-style namespaced keys (e.g. nuclio.io/function-spec, or any domain/key convention) therefore produce a Prometheus label name containing a literal /, which is not a valid character in a Prometheus label name.

This isn't just a cosmetic issue with that one label: it breaks the Prometheus text exposition format parser for scrapers that enforce it strictly (we hit this with Grafana Alloy). The scrape fails to parse the entire /metrics response, so every metric from that target is lost, not just the one with the bad label.

Example

A container with the Docker label:

nuclio.io/function-spec: {...}

Currently produces:

container_label_nuclio_io/function_spec="{...}"

(the . is escaped to _, but the / is not) — this is invalid Prometheus exposition syntax and causes the whole scrape to fail parsing.

With the fix, it produces:

container_label_nuclio_io_function_spec="{...}"

which parses correctly.

Fix

Add / to the existing escape_list alongside -, ., : and in ProcessTracker's container label handling. PR: #440