fix(ls-api): align mock with LocalStack API and add regression test

[joe4dev]

Motivation

The LocalStack ↔ RIE API contract (the HTTP endpoints that LocalStack calls on the RIE and vice versa) is currently unversioned. This is especially risky for Kubernetes deployments, where LocalStack and the Lambda container images (which embed the RIE) can be at different versions with no coordination mechanism. A silent mismatch — e.g. a renamed JSON field or a changed status code — would cause invocations to fail with no clear error.

This PR adds a regression test suite that pins the exact contract so that future changes are caught at review time rather than in production.

Changes

cmd/ls-api/main.go — align mock with executor_endpoint.py

The existing mock was drifting from the real LocalStack API in several ways, which would have caused the new tests to pass incorrectly if left unfixed:

• All handlers now return 202 Accepted to match executor_endpoint.py (previously all defaulted to 200 OK)
• invokeErrorHandler now reads and logs the request body (was a no-op)
• invokeLogsHandler now decodes the {"logs":"..."} JSON structure instead of reading raw bytes
• InvokeRequest gains the missing invoked-function-arn and trace-id fields that custom_interop.go actually sends
• LogResponse struct extracted and documented
• log.Fatal in the statusHandler goroutine downgraded to log.Error (would have called os.Exit on any connection failure, including during tests)

cmd/ls-api/main_test.go — new regression tests

7 unit tests covering the full LS↔RIE API surface:

Test	What it pins
TestInvocationResponseReturns202	POST /invocations/{id}/response → 202
TestInvocationErrorReturns202	POST /invocations/{id}/error → 202
TestInvocationLogsReturns202	POST /invocations/{id}/logs with {"logs":"..."} → 202
TestStatusReadyReturns202AndTriggersInvoke	POST /status/{id}/ready → 202 + async invoke dispatched
TestStatusErrorReturns202	POST /status/{id}/error → 202
TestInvokeRequestJSONFieldNames	All four JSON field names LocalStack sends to /invoke
TestLogResponseJSONFieldName	The "logs" key the RIE sends back to LocalStack

TestInvokeRequestJSONFieldNames carries an explicit warning comment that the LS↔RIE API is unversioned and that field-name changes are silent breaking changes requiring coordinated releases of both repos.

[dfangl]

I'm not quite sure what the purpose of this PR is - where is this ls-api mock used? It definitely improves the mock, but I don't quite understand where the mock itself is used and how we use it to test regressions?

[joe4dev]

I'm not quite sure what the purpose of this PR is - where is this ls-api mock used? It definitely improves the mock, but I don't quite understand where the mock itself is used and how we use it to test regressions?

Sorry for the noise. You're spot on. Converted back to draft.

The test is not even using the mock nor the other code 🤦

[dfangl]

The test is not even using the mock nor the other code 🤦

It's using the handlers of the mock at least, but that is about it :)