fix: preserve admin auth effective config

[intel352]

Summary

• preserve admin auth effective_config through the strict typed describe path
• recover safe admin config keys from prior step outputs for describe-only flows
• whitelist effective/accepted auth config keys so request headers and other pipeline data are not echoed

Tests

• GOWORK=off go test ./internal -run 'TestTypedAuthAdminConfigDescribePreservesEffectiveConfig|TestAuthAdminConfigDescribeExposesRealConfigControls|TestAuthAdminConfigValidateAcceptsPasskeyPatchAndRedactsSecrets' -count=1
• GOWORK=off go test ./... -count=1

[Copilot]

Pull request overview

This PR updates the strict-typed (protobuf) step handling for step.auth_admin_config_describe so admin-auth “effective_config” is preserved through typed execution, while also preventing unrelated pipeline/request data (e.g., headers) from being echoed back in describe outputs.

Changes:

• Add a dedicated typed handler for step.auth_admin_config_describe that can recover effective admin-auth config from prior step outputs during describe-only flows.
• Introduce an allowlist for admin-auth config keys to ensure only intended configuration fields can appear in effective_config / accepted_config.
• Add a regression test ensuring effective config is preserved and request headers are not leaked.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
internal/typed.go	Adds a custom typed handler for admin config describe and merges recovered config into the typed current.
internal/step_admin_config.go	Replaces ad-hoc sanitization with an allowlisted key filter; adds helpers to recover safe config keys from step outputs.
internal/plugin.go	Switches the typed step factory wiring for step.auth_admin_config_describe to the new handler.
internal/plugin_contracts_test.go	Adds a typed regression test for preserving effective_config while preventing header leakage.

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