permissions: add built-in default profiles (#19900)

## Why

The migration away from `SandboxPolicy` needs new configs to start from
permissions profiles instead of deriving profiles from legacy sandbox
modes. Existing users can have empty `config.toml` files, and we should
not rewrite user-owned config files that may live in shared
repositories.

This PR introduces built-in profile names so an empty config can resolve
to a canonical `PermissionProfile`, while explicit named `[permissions]`
profiles still behave predictably.

## What changed

- Adds built-in `default_permissions` profile names:
  - `:read-only` maps to `PermissionProfile::read_only()`.
- `:workspace` maps to the workspace-write profile, including
project-root metadata carveouts.
- `:danger-no-sandbox` maps to `PermissionProfile::Disabled`, preserving
the distinction between no sandbox and a broad managed sandbox.
- Reserves the `:` prefix for built-in profiles so user-defined
`[permissions]` profiles cannot collide with future built-ins.
- Allows `default_permissions` to reference a built-in profile without
requiring a `[permissions]` table.
- Makes an otherwise empty config choose a built-in profile by
trust/platform context: trusted or untrusted project roots use
`:workspace` when the platform supports that sandbox, while roots
without a trust decision use `:read-only`.
- Keeps legacy `sandbox_mode` configs on the legacy path, and still
rejects user-defined `[permissions]` profiles that omit
`default_permissions` so we do not silently guess among custom profiles.
- Preserves compatibility behavior for implicit defaults: bare
`network.enabled = true` allows runtime network without starting the
managed proxy, explicit profile proxy policy still starts the proxy, and
implicit workspace/add-dir roots keep legacy metadata carveouts.

## Verification

- `cargo test -p codex-core builtin --lib`
- `cargo test -p codex-core profile_network_proxy_config`
- `cargo test -p codex-core
implicit_builtin_workspace_profile_preserves_add_dir_metadata_carveouts`
- `cargo test -p codex-core
permissions_profiles_network_enabled_allows_runtime_network_without_proxy`
- `cargo test -p codex-core
permissions_profiles_proxy_policy_starts_managed_network_proxy`

## Documentation

Public Codex config docs should mention these built-in names when the
`[permissions]` config format is ready to document as stable.









---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/openai/codex/pull/19900).
* #20041
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* __->__ #19900

codex-rs/core/tests/suite/hooks.rs

@@ -3,12 +3,6 @@ use std::path::Path;
 
 use anyhow::Context;
 use anyhow::Result;
-use codex_config::ConfigLayerStack;
-use codex_config::ConfigLayerStackOrdering;
-use codex_config::NetworkConstraints;
-use codex_config::NetworkRequirementsToml;
-use codex_config::RequirementSource;
-use codex_config::Sourced;
 use codex_core::config::Constrained;
 use codex_features::Feature;
 use codex_protocol::items::parse_hook_prompt_fragment;
@@ -21,6 +15,7 @@ use codex_protocol::protocol::RolloutItem;
 use codex_protocol::protocol::RolloutLine;
 use codex_protocol::protocol::SandboxPolicy;
 use codex_protocol::user_input::UserInput;
+use core_test_support::managed_network_requirements_loader;
 use core_test_support::responses::ev_apply_patch_function_call;
 use core_test_support::responses::ev_assistant_message;
 use core_test_support::responses::ev_completed;
@@ -1577,6 +1572,7 @@ allow_local_binding = true
                 panic!("failed to write permission request hook test fixture: {error}");
             }
         })
+        .with_cloud_requirements(managed_network_requirements_loader())
         .with_config(move |config| {
             config
                 .features
@@ -1586,33 +1582,6 @@ allow_local_binding = true
             config
                 .set_legacy_sandbox_policy(sandbox_policy_for_config)
                 .expect("set sandbox policy");
-            let layers = config
-                .config_layer_stack
-                .get_layers(
-                    ConfigLayerStackOrdering::LowestPrecedenceFirst,
-                    /*include_disabled*/ true,
-                )
-                .into_iter()
-                .cloned()
-                .collect();
-            let mut requirements = config.config_layer_stack.requirements().clone();
-            requirements.network = Some(Sourced::new(
-                NetworkConstraints {
-                    enabled: Some(true),
-                    allow_local_binding: Some(true),
-                    ..Default::default()
-                },
-                RequirementSource::CloudRequirements,
-            ));
-            let mut requirements_toml = config.config_layer_stack.requirements_toml().clone();
-            requirements_toml.network = Some(NetworkRequirementsToml {
-                enabled: Some(true),
-                allow_local_binding: Some(true),
-                ..Default::default()
-            });
-            config.config_layer_stack =
-                ConfigLayerStack::new(layers, requirements, requirements_toml)
-                    .expect("rebuild config layer stack with network requirements");
         })
         .build(&server)
         .await?;