[jonathan343]

Summary

The InterceptorChain currently passes the original context to every interceptor, so a modify_* hook's result gets lost whenever another interceptor runs after it on the same hook. That includes the base Interceptor defaults, which returned the original value. Additionally, modify_before_completion incorrectly calls each interceptor's modify_before_attempt_completion. In 11 of the 12 read hooks, one raising interceptor kept every later interceptor from running. Separately, RequestPipeline serialized and resolved endpoints from call.input, so the request returned by modify_before_serialization never reached the wire.

This PR passes each interceptor's result to the next interceptor and makes modify_before_completion call its own hook. Every read hook now runs all interceptors before raising the last error, as the Smithy interceptor guide specifies for immutable hooks. Earlier errors are logged at debug level, and read_after_attempt passes each error on to later interceptors, as read_after_execution already did. The pipeline now uses the modified request for serialization, endpoint resolution, and the serialization error path. A modify_* hook that returns None now raises TypeError instead of passing None to the next interceptor.

Before / After

from typing import Any

from smithy_core.interceptors import Interceptor, InterceptorChain, RequestContext
from smithy_core.types import TypedProperties


class AddHeader(Interceptor[Any, Any, Any, Any]):
    def __init__(self, name: str) -> None:
        self.name = name

    def modify_before_signing(self, context: RequestContext[Any, Any]) -> Any:
        return {**context.transport_request, self.name: "1"}


class Fails(Interceptor[Any, Any, Any, Any]):
    def read_before_signing(self, context: RequestContext[Any, Any]) -> None:
        raise RuntimeError("first interceptor failed")


class Logs(Interceptor[Any, Any, Any, Any]):
    def read_before_signing(self, context: RequestContext[Any, Any]) -> None:
        print("second interceptor ran")


context = RequestContext(request=None, transport_request={}, properties=TypedProperties())

chain = InterceptorChain([AddHeader("x-a"), AddHeader("x-b"), Interceptor()])
print("headers:", chain.modify_before_signing(context))

try:
    InterceptorChain([Fails(), Logs()]).read_before_signing(context)
except RuntimeError as e:
    print("raised:", e)

Before

headers: {}
raised: first interceptor failed

After

headers: {'x-a': '1', 'x-b': '1'}
second interceptor ran
raised: first interceptor failed

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