Fix Serena MCP server URL to use host.docker.internal

[Copilot]

The MCP gateway container was trying to connect to Serena at http://localhost:9121, which resolves to the container itself rather than the host where Serena runs.

Changes

• Updated Serena MCP server URL from localhost:9121 to host.docker.internal:9121 in both JSON and TOML config renderers
• Updated test expectations to reflect the new URL pattern
• Recompiled all affected workflow lock files

This aligns with the existing pattern used by safe-inputs server (http://host.docker.internal:3000).

Context

# Gateway configuration (sent to container)
"serena": {
  "type": "http",
  "url": "http://host.docker.internal:9121"  # Now reaches host
}

# Health check (runs on host)
curl -s http://localhost:9121/health  # Still correct

The health check step correctly uses localhost since it runs on the host, while the gateway config uses host.docker.internal for container-to-host communication.

Original prompt

Reference: https://github.com/githubnext/gh-aw/actions/runs/20955104811/job/60217714408#step:47:1

Debug why the MCP gateway failed

Custom agent used: agentic-campaigns
GitHub Agentic Campaigns - Create and manage multi-workflow campaigns for coordinated automation at scale

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