Windows server tests assume unescaped paths and POSIX settings lookup #30950

Problem

On Windows at upstream main 9e85538535c8553901351112ab02dd1dd62db5ee, 17 server test failures come from three platform assumptions. The affected files pass in Linux CI: https://github.com/pingdotgg/t3code/actions/runs/41841763173 . These are test bugs; production path quoting and settings lookup should remain unchanged.

1. JSON-escaped paths (15 failures): ClaudeAdapterV2.test.ts searches JSON-serialized payloads for raw Windows paths. userInputAttachments.test.ts expects raw paths where production deliberately JSON-quotes references. Compare decoded payload fields or correctly encoded expected values at the relevant serialization depth.
2. Claude settings lookup (1 failure): a settings test assumes POSIX worktree-to-repository-root lookup. Windows intentionally uses the current working directory. Make the expected values platform-aware without weakening the POSIX assertions.
3. Codex path separator (1 failure): CodexDriver.test.ts expects the literal suffix providers/codex/restored-managed-account/shadow. Build it with NodePath.join.

The Windows ACP detached .cmd hang is a separate production issue tracked in #29088 and #30544; it does not belong in this test-only change.

Expected correction

One small PR covering these three test assumptions, with focused verification on Windows and unchanged production code. Preserve assertions about actual attachment content, settings selection and restored account paths; do not skip tests or hide the failures.

The failure inventory and causes were supplied by Elliot's Windows research audit. No new diagnosis of those established baseline failures is needed.