[codex] Add danger-full-access denylist-only network mode

[viyatb-oai]

Summary

This adds experimental_network.danger_full_access_denylist_only for orgs that want yolo / danger-full-access sessions to keep full network access while still enforcing centrally managed deny rules.

When the flag is true and the session sandbox is danger-full-access, the network proxy starts with:

• domain allowlist set to *
• managed domain deny entries enforced
• upstream proxy use allowed
• all Unix sockets allowed
• local/private binding allowed

Caveat: the denylist is best effort only. In yolo / danger-full-access mode, Codex or the model can use an allowed socket or other local/private network path to bypass the proxy denylist, so this should not be treated as a hard security boundary.

The flag is intentionally scoped to SandboxPolicy::DangerFullAccess. Read-only and workspace-write modes keep the existing managed/user allowlist, denylist, Unix socket, and local-binding behavior. This does not enable the non-loopback proxy listener setting; that still requires its own explicit config.

This also threads the new field through config requirements parsing, app-server protocol/schema output, config API mapping, and the TUI debug config output.

How to use

Add the flag under [experimental_network] in the network policy config that is delivered to Codex. The setting is not under [permissions].

[experimental_network]
enabled = true
danger_full_access_denylist_only = true

[experimental_network.domains]
"blocked.example.com" = "deny"
"*.blocked.example.com" = "deny"

With that configuration, yolo / danger-full-access sessions get broad network access except for the managed denied domains above. The denylist remains a best-effort proxy policy because the session may still use allowed sockets to bypass it. Other sandbox modes do not get the wildcard domain allowlist or the socket/local-binding relaxations from this flag.

Verification

• cargo test -p codex-config network_requirements
• cargo test -p codex-core network_proxy_spec
• cargo test -p codex-app-server map_requirements_toml_to_api
• cargo test -p codex-tui debug_config_output
• cargo test -p codex-app-server-protocol
• just write-app-server-schema
• just fmt
• just fix -p codex-config -p codex-core -p codex-app-server-protocol -p codex-app-server -p codex-tui
• just fix -p codex-core -p codex-config
• git diff --check
• cargo clean