## Why
Sandboxed exec-server process requests can use a restricted filesystem
profile that does not expose the exec-server binary. On Linux, the outer
bubblewrap stage re-enters that binary with the `codex-linux-sandbox`
argv0 to install seccomp, so hiding the binary prevents the requested
process from starting.
## What changed
- add the configured `codex_self_exe` to the process permission profile
before constructing the outer platform sandbox
- add a Linux exec-server integration test that starts a real remote
process with restricted reads and verifies it can read an allowed
workspace file
## Test plan
- `just test -p codex-exec-server process_sandbox`
- `just test -p codex-exec-server --test exec_process
remote_process_keeps_sandbox_helper_visible_with_restricted_reads`
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