fix(runtime): resolve codex .cmd shim path so Windows spawns don't fail

[AbirAbbas]

Summary

On Windows, every codex harness call fails instantly with [WinError 2] The system cannot find the file specified. _run_codex_cli_with_stdin in swe_af/runtime/codex_harness_patch.py spawns the bare "codex" name via asyncio.create_subprocess_exec, but CreateProcess does no PATHEXT resolution and npm installs the codex CLI only as a .cmd shim — so the spawn never finds it, even though the shell does.

The AgentField SDK already ships the fix for exactly this (agentfield.harness._cli.resolve_cli_command, which resolves the shim's real path via shutil.which and is a no-op on POSIX), but this monkeypatch bypasses the SDK's spawn path and never picked it up. Mac/Linux never hit the bug, which is how it went unnoticed.

Symptoms

• Any reasoner using the codex runtime on a Windows node fails in ~500ms with its fallback result (e.g. retry advisor returns "Retry advisor agent failed to produce a valid analysis").
• Node log shows Schema validation retry N/2: The output file was NOT created. followed by Schema retry N provider error: [WinError 2] The system cannot find the file specified.

Changes Made

• Route cmd[0] through the SDK's resolve_cli_command before create_subprocess_exec (no-op on POSIX and for paths that already carry a separator).
• Regression test asserting the spawn receives the resolved command, with args and stdin passthrough unchanged.

Test Plan

• make check green (1130 passed, 1 skipped) on Python 3.12
• Verified on a real Windows node: with this patch applied to the installed package, run_retry_advisor invoked with ai_provider=codex / model=gpt-5.6-luna returns real structured advice through the codex CLI (previously the instant WinError 2 fallback)

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