[Bug]: WebServer route layer doesn't URL-decode path segments #222

Summary

dex-local-runner (WebRunner) returns 404 for every Get/State/History/Checkpoint/Stop call against an execution whose ARN contains a literal /, and silently returns an empty list for ListDurableExecutionsByFunction when the function name contains : or $. The cause is that the WebServer's route layer does not URL-decode captured path segments before using them as store-lookup keys, while boto's rest-json serializer percent-encodes those characters in non-greedy URI labels.

Affected versions

aws-durable-execution-sdk-python-testing == 1.2.0 (PyPI). The bug was introduced in #216 (which started minting ARNs of the form <uuid>/<invocation-id>) and shipped in v1.2.0.

Affected runners

• WebRunner / dex-local-runner — broken for every nontrivial durable function, since the first context.step / context.wait / context.callback triggers a checkpoint call that 404s.
• DurableFunctionTestRunner (in-process) — not affected; uses InMemoryServiceClient which ignores durable_execution_arn.
• DurableFunctionCloudTestRunner (real AWS) — not affected; ARNs come from the real Lambda backend and never round-trip through the local route layer.

Affected operations

All five durable-execution operations whose URI label is the ARN, plus the by-function list:

For non-greedy labels (no +), boto encodes:

• / → %2F
• : → %3A
• $ → %24

Reproduction

import boto3
from aws_durable_execution_sdk_python_testing import WebRunner, WebRunnerConfig
from aws_durable_execution_sdk_python_testing.web.server import WebServiceConfig

with WebRunner(WebRunnerConfig(web_service=WebServiceConfig(port=0))) as runner:
    # ...start an execution via runner so a slash-containing ARN is minted...
    arn = "<uuid>/<invocation-id>"  # the format Execution.new() produces
    client = boto3.client("lambda", endpoint_url="http://127.0.0.1:<port>", ...)
    client.get_durable_execution(DurableExecutionArn=arn)
    # botocore.exceptions.ClientError:
    #   An error occurred (404) when calling the GetDurableExecution operation:
    #   Execution <uuid>%2F<invocation-id> not found

The %2F literal in the error message is the giveaway — the WebServer is looking up the still-encoded form rather than the canonical ARN.

Why nothing caught it

• All routing tests use slash-free literals like "test-arn" or "my-function", so Route.from_string never produced a segment containing %XX.
• All boto3.client usages in the test suite are mocked (patch("boto3.client")), so the real botocore serializer that does the encoding is never exercised.
• The integration test in tests/web/e2e/server_int_test.py constructs HTTPRequest objects in-process and bypasses the HTTP/socket layer.
• The headline e2e test (tests/e2e/basic_success_path_test.py) uses DurableFunctionTestRunner, which doesn't go through the affected route layer.
• CI runs only hatch test / hatch fmt --check / hatch run types:check; no test exercised the boto→WebServer seam.

#117 fixed the same bug shape for callback IDs but the systemic fix (decode at the parser layer) was not applied at the time.

Expected fix

URL-decode captured path segments at the parser layer (Route.from_string) so every existing and future captured field inherits the behavior, and add a real-boto-through-WebServer regression test so the seam stays covered. PR forthcoming.