## Why
Private `/tmp` bind mounts can leave hidden entries in `/proc/self/mountinfo`, causing the Linux sandbox to reject layouts that safely isolate daemon sockets. The proc-mount preflight also needs the main sandbox's WSL masks when checking aliases.
## What changed
- Identify the opened socket directory's mount using `fdinfo`, with a `statx` fallback, and follow its mount ancestry to distinguish hidden paths from exposed aliases.
- Accept safe private and stacked mounts while rejecting covered mounts, exposed aliases, and nested mounts. Retain conservative checks when no mount ID is available.
- Preserve WSL interop and WSLg masks in the proc-mount preflight.
- Heap-allocate large lifecycle futures in the TUI approval-gated MCP tool test to reduce Windows test-thread stack usage.
## Testing
Add mount-layout regression cases and a namespace integration test that verifies daemon sockets remain inaccessible under private `/tmp`, unrelated sockets remain reachable, and an exposed alias prevents startup. Add a preflight test for preserving WSL masks.
GitOrigin-RevId: 289b4446ba7776a7dd57ef5ff09e87bda19b069c
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