Scaling based on a number of active calls fixed and filtering by sipTrunkId

[rafallezanko]

There was existing TODO to fix -> Scale outbound calls based on number or active calls.

Load-aware affinity routing and trunk whitelisting for SIP bridges

Summary

• Implement CreateSIPParticipantAffinity to return a dynamic score based on the number of active calls (inbound + outbound),
  replacing the hardcoded 0.5. This enables psrpc to route new outbound calls to the least-loaded SIP bridge.
• Add sip_trunk_ids config option to restrict a SIP bridge to only serve specific trunk IDs, enabling dedicated gateways per
  trunk.

Affinity algorithm

The function evaluates in order:

1. Trunk whitelist (sip_trunk_ids) — if configured and the request's trunk ID is not in the list, return 0 immediately (this node
   will not claim the call).
2. Capacity limit (max_active_calls) — if configured, return 1 - (active / max). Returns 0 when at or over capacity.
3. Fallback (no max_active_calls) — return 1 / (1 + active). No hard cap, but nodes with fewer calls are always preferred.

Configuration

Optional: maximum number of concurrent calls this bridge should handle.
Affinity scales linearly from 1.0 (idle) to 0.0 (at capacity).
max_active_calls: 100

Optional: only accept outbound calls for these trunk IDs.
Calls for any other trunk will get affinity 0 (routed elsewhere).
If empty/unset, all trunks are accepted.
sip_trunk_ids:
- "ST_abc123"
- "ST_def456"

[codecov]

Codecov Report

❌ Patch coverage is 87.50000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 63.07%. Comparing base (0460b40) to head (cfd3770).
⚠️ Report is 229 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/sip/service.go	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #598      +/-   ##
==========================================
- Coverage   65.25%   63.07%   -2.18%     
==========================================
  Files          51       35      -16     
  Lines        6588     6920     +332     
==========================================
+ Hits         4299     4365      +66     
- Misses       1915     2128     +213     
- Partials      374      427      +53     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.