Return the set of agent names configured in config.toml — the global
[workers].agent (defaulting to “claude” when absent) plus the agent
of every [worker_profiles.*] entry.
Layer 1 of the two-layer manifest validation design.
Validates all configured agent names and scans .apm/agents/ for issues.
Returns (errors, warnings) so callers can route them — keeps this single
directory scan from running twice when both validate_config and
validate_warnings are invoked.
Walk every non-closed ticket and return a vec of (subject, message) pairs
for each ticket whose depends_on violates the active completion strategy rule.