Gate the POSIX-only and symlink-only tests with the linux_only and
require_symlinks markers. Fix the real cross-platform bugs:
- file_operations: use the translate_path flag, send snippets as base64, and
use sys.executable (the MS Store python3 stub and the list2cmdline
backslash collapse both broke snippets)
- approval: treat backslash as a Windows path separator, not an escape
- registry, browser_registry, secret_sources, plugins: normalize scope-key case
- checkpoint_manager, plugins_cmd: clear read-only bits before delete
- deadline: make MAX_SAFE_TIMEOUT_S fit the Windows limit
- image_routing, acp, cua_backend, daytona: fix Windows and POSIX paths
- hermes_state: match backslash in the retag LIKE clause
- kanban, disk-cleanup: match drive paths and split command arguments
- scripts: emit host separators through as_posix
207 test files are gated or isolated.
bd258480d3