[chore][MCP] Configure backend MCP service ingress domain

[arnold-retool]

Summary

• Inject MCP_SERVICE_INGRESS_DOMAIN into the main backend when MCP is enabled.
• Derive the internal URL from the release-specific MCP Service name and configured external port.
• Preserve explicit overrides from env, environmentSecrets, or environmentVariables.
• Update both synchronized values.yaml files to document the automatic configuration.

Testing

• helm lint charts/retool
• helm template with test-install-values.yaml and test-mcp-enabled-option.yaml
• Verified MCP-disabled, default, custom Service name/port, and explicit override renders
• Confirmed values.yaml and charts/retool/values.yaml remain synchronized
• git diff --check

[greptile-apps]

Confidence Score: 5/5

Safe to merge — the change is additive (new env var only when MCP is enabled), override detection covers all three env-setting paths, and the helper follows the exact same pattern already used for agent sandbox env vars.

The new helper correctly gates injection on mcp.enabled, de-duplicates against all three override mechanisms using established Helm patterns, and defaults gracefully when mcp.service is absent. The nindent 10 on empty output is the same pattern used by the adjacent retool.agentSandbox.backendEnvVars call. Both values.yaml files are kept in sync and the docs accurately describe the new automatic behavior.

Files Needing Attention: No files require special attention.

Important Files Changed

Filename	Overview
charts/retool/templates/_helpers.tpl	Adds retool.mcp.backendEnvVars helper that auto-injects MCP_SERVICE_INGRESS_DOMAIN for MCP-enabled installs, with correct override detection across all three env-setting mechanisms (env, environmentSecrets, environmentVariables)
charts/retool/templates/deployment_backend.yaml	Single-line inclusion of the new retool.mcp.backendEnvVars helper, positioned correctly in the env block alongside other service-discovery env vars
charts/retool/values.yaml	Documentation updated to reflect the charts new automatic MCP_SERVICE_INGRESS_DOMAIN injection, replacing the manual env block example with a description of the auto-config and override path
values.yaml	Mirror of charts/retool/values.yaml documentation update; kept in sync as required

_{Reviews (1): Last reviewed commit: "[chore][MCP] Configure backend MCP servi..." | Re-trigger Greptile}

[lukefoster11]

Not sure if we need to check all these different places for MCP_SERVICE_INGRESS_DOMAIN being defined. I think we can narrow these checks down to just .Values.env.
Also wondering if there's ever even a case where the MCP_SERVICE_INGRESS_DOMAIN shouldn't just be set to value: {{ printf "http://%s:%v" (include "retool.mcp.name" .) ($mcpService.externalPort | default 4010) | quote }}? Should we even allow overriding this default?

[arnold-retool]

• Just .Values.env could make setup less straightforward for users with .environmentSecrets and .environmentVariables in their charts.
• An override is generally useful in cases with custom networking. I can't imagine users taking advantage of this override to break things for themselves.

Thanks for the comment! Let me know if you feel strongly about either of these.