Make GCP Redis engine version configurable

[dobrac]

Make GCP Redis engine version configurable to allow changes between environments.

[cursor]

PR Summary

Low Risk
Low risk: this only parameterizes the GCP Memorystore engine version with a default, without changing resource topology or core runtime logic.

Overview
Makes the managed GCP Redis/Valkey engine version configurable by adding a new Terraform input (defaulting to VALKEY_8_0) that can be set via GCP_REDIS_ENGINE_VERSION/TF_VAR_gcp_redis_engine_version, and wiring it through to the Redis module to replace the previously hardcoded Memorystore engine_version.

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[claude]

Review posted

[claude]

LGTM — straightforward config change wiring engine version through the Terraform variable chain; the nit about missing validation is noted in the inline comment.

Extended reasoning...

Overview

This PR replaces the hardcoded "VALKEY_8_0" string in iac/provider-gcp/redis/main.tf with a new engine_version variable, propagated all the way from a new GCP_REDIS_ENGINE_VERSION env var through the Makefile tfvar bridge and the provider-level gcp_redis_engine_version variable. Six files are touched, but the changes are purely mechanical plumbing with a safe default (VALKEY_8_0) that preserves existing behavior.

Security Risks

None. This is infrastructure configuration with no auth, crypto, or permission implications. The variable only affects the Memorystore engine version string passed to GCP.

Level of Scrutiny

Low. The change is a textbook "extract hardcoded value into variable" refactor. The wiring is complete and consistent across all layers (env template → Makefile → root variables.tf → module call → redis/variables.tf → resource). The only finding is a nit-level absence of a validation block, which is already surfaced as an inline comment.

Other Factors

No CODEOWNER files appear to govern these Terraform modules based on the repo structure. The inline comment covers the one actionable nit; it does not block correctness or safety of the change.