python-aws-emulator-response-shape

Answer

Root cause (BUG-002). The assembler generated handlers that returned only the AWS-nested shape ({"PolicySummary": {...}}), while integration tests assert flat top-level keys (PolicyName, PolicyId, …). A second defect: the handler manifest was hand-maintained and omitted delete-experiment, so even though the store method existed, emulator/handlers/delete-experiment.py was never generated and the router died with FileNotFoundError at import.

Fix 1 — flat + nested coexist. A single response builder spreads the payload flat and attaches the AWS wrapper:

# emulator/shape.py
import copy
from typing import Any, Mapping

_UNSET = object()

def merged_response(payload, *, wrappers=None, content=_UNSET):
    """{**payload, <wrapper>: deepcopy(payload)..., "Content": ...}"""
    wrapper_names = () if wrappers is None else \
        ((wrappers,) if isinstance(wrappers, str) else tuple(wrappers))
    response = dict(payload)                       # flat keys (integration)
    for name in wrapper_names:
        response[name] = copy.deepcopy(dict(payload))  # nested (e2e)
    if content is not _UNSET:
        response["Content"] = content
    return response

Assembled handlers now emit:

# handlers/get-policy.py (generated)
name = event["name"]
summary = _store.get_policy(name)
document = _store.get_policy_document(name)
return merged_response(summary, wrappers="PolicySummary", content=document)
# -> {"PolicyName": ..., "PolicyId": ..., "Arn": ..., "PolicySummary": {...}, "Content": '{"Version":...}'}

# handlers/delete-experiment.py (generated)
state = _store.delete_experiment(event["experimentId"])
return merged_response(state, wrappers="state")   # flat keys + nested state dict

Fix 2 — handler files can't go missing again. The manifest is now derived from the store's own methods (build_manifest() introspects dir(PolicyStore)), so every store method gets a generated file; the router additionally loads hyphenated files from disk and, as a defensive fallback, resolves missing files to a dynamic store-calling handler instead of raising FileNotFoundError.