Affected: npm: openclaw

### Summary Sandbox media handling had a time-of-check/time-of-use gap: media paths could be validated first and read later through a separate path. A symlink retarget between those steps could cause reads outside `sandboxRoot`.

### Impact Affected versions could permit host file reads outside the intended sandbox root in media attachment/image flows.

### Fix Media reads now use consolidated root-scoped, boundary-safe read paths at use time, removing check/use drift across call sites.

### Affected and Patched Versions - Affected: `<= 2026.2.26` - Patched: `2026.3.1`