[codex] Reduce idle dev SQS polling

[manynames3]

Summary

• disable the Lambda SQS event source mapping by default in dev while preserving staging and production defaults
• keep 20-second long polling on the processing queue and DLQ
• add processor polling configuration logs and the NumberOfEmptyReceives dashboard metric
• document intentional dev worker operation and CloudWatch verification
• add Terraform plan tests and run them in CI

Root cause

The repository has no application-side SQS polling loop. The always-enabled Lambda event source mapping continuously polls grantstack-dev-processing while idle. Because AWS owns that polling loop, adding sleep or jitter inside the processor Lambda would not affect empty receives.

Impact

Dev messages remain queued until enable_sqs_worker = true is applied. Staging and production remain enabled by default. Queues, DLQs, partial batch failure behavior, and the existing 960-second visibility timeout are preserved.

Batch size remains one because a single report can use the processor's 900-second timeout.

Validation

• terraform fmt -check -recursive
• terraform validate
• terraform test (3 passed)
• Python compile checks
• python3 -m unittest discover -s grantstack-backend/tests (19 passed)
• git diff --check

[gemini-code-assist]

Code Review

This pull request introduces a mechanism to disable the SQS Lambda event source mapping by default in the development environment to prevent empty-receive charges, while keeping it enabled in staging and production. It includes updated documentation, runbooks, Terraform configuration, tests, and enhanced logging in the processor Lambda. A review comment suggests improving the robustness of the Lambda handler by safely handling cases where the input event or its 'Records' key is null, preventing potential TypeErrors.

Important

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[gemini-code-assist]

If event is None or if the "Records" key is explicitly set to null (which parses as None in Python), calling event.get("Records", []) will return None. This will subsequently cause a TypeError when len(records) is evaluated on line 69, or a TypeError when iterating over records on line 72.

To make this more robust and adhere to defensive programming practices, use a guard to handle both None event and None records cases.

Suggested change

	records = event.get("Records", [])
	records = event.get("Records") or [] if event else []