fix(gateway): preserve final delivery on non-editable streams

[devatnull]

Summary

• skip gateway streaming previews for non-editable adapters in the proxy path
• preserve final delivery on WhatsApp/Signal-style transports by letting the normal final send path run once
• add direct and proxy regression coverage for non-editable streaming

Why

Non-editable messaging platforms cannot replace a stream preview with the final answer. If a preview is sent first, final delivery can be suppressed or duplicated. The direct agent path already guarded this; this PR applies the same guard to proxy-mode streaming and tests both paths.

Test plan

• python3 -m pytest tests/gateway/test_run_progress_topics.py::test_proxy_non_editable_streaming_uses_final_delivery_only tests/gateway/test_run_progress_topics.py::test_run_agent_non_editable_streaming_uses_final_delivery_only -q
• scripts/run_tests.sh tests/gateway/test_run_progress_topics.py -q
• python3 -m py_compile gateway/run.py tests/gateway/test_run_progress_topics.py
• git diff --check origin/main...HEAD

[Copilot]

Pull request overview

This PR aligns proxy-mode streaming behavior with the existing direct-agent behavior for non-editable messaging adapters, preventing streaming “preview” deliveries that can’t be edited into a final message on platforms without message-edit support.

Changes:

• Skip gateway stream-consumer setup for adapters that don’t support message editing in the proxy streaming path.
• Add regression tests covering both direct and proxy execution paths to ensure non-editable adapters do not receive progressive streaming sends and that final delivery remains eligible to run once.
• Validate proxy SSE parsing still produces the correct assembled final_response while reporting response_previewed=False when previews are suppressed.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
gateway/run.py	Disables proxy-path streaming previews on non-editable adapters so final delivery isn’t suppressed/duplicated.
tests/gateway/test_run_progress_topics.py	Adds direct + proxy regression coverage ensuring non-editable adapters do not receive streaming preview sends.

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[teknium1]

Thanks for the focused proxy-path fix. Current main still constructs a GatewayStreamConsumer for non-editable adapters in proxy mode at gateway/run.py:17023-17055; the consumer can send a first streamed chunk through adapter.send() (gateway/stream_consumer.py:928-942). The proxy result then reports response_previewed when that consumer exists (gateway/run.py:17188-17199).

The proposed guard matches the existing direct-agent behavior at gateway/run.py:18347-18354, and the added proxy regression test covers the previously unguarded path. The only production construction sites are the proxy and direct paths (rg -n 'GatewayStreamConsumer\\('); the direct path is already guarded.

Automated hermes-sweeper review.