Add gateway HTTP behavior tests

[binrogithub]

Motivation

• Add tests to validate gateway/runner HTTP behavior for preview and apply modes, and to ensure gateway persistence of run artifacts when a RunStore is available.
• Ensure preview runs do not make outbound HTTP calls and still produce artifacts when run via a gateway path.
• Ensure apply runs invoke HTTP exactly once and that run evidence is filtered to whitelisted keys.

Description

• Add tests/test_preview_no_http.py which patches requests.request to raise an AssertionError if called, invokes a preview run via any available gateway/runner callable (e.g. hc_run/run), asserts the run result indicates success or a non-HTTP error, asserts requests.request was not called, and checks artifact files when a gateway path is used.
• Add tests/test_apply_calls_http.py which patches requests.request to return a FakeResponse (200, X-Request-Id header, JSON payload), invokes an apply run, asserts requests.request was called once, validates presence of expected run fields (e.g. run_id/summary/envelope), and enforces evidence keys are whitelisted.
• Add tests/test_gateway_persists_run.py which detects an available RunStore class, instantiates it pointing at a temp base dir, runs the gateway apply path, extracts the run id from the result, and asserts an artifact like runs/<run_id>/report.md exists.
• Tests are written to discover available modules/entrypoints at runtime and to skip when required dependencies or signatures are not present; all mocking uses autotest.client.shared.test_utils.mock.
• No external skills were used for this change.

Testing

• No automated tests were executed as part of this change.

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Codex Task