feat: make sandbox read access configurable with ReadOnlyAccess (#11387)

`SandboxPolicy::ReadOnly` previously implied broad read access and could
not express a narrower read surface.
This change introduces an explicit read-access model so we can support
user-configurable read restrictions in follow-up work, while preserving
current behavior today.

It also ensures unsupported backends fail closed for restricted-read
policies instead of silently granting broader access than intended.

## What

- Added `ReadOnlyAccess` in protocol with:
  - `Restricted { include_platform_defaults, readable_roots }`
  - `FullAccess`
- Updated `SandboxPolicy` to carry read-access configuration:
  - `ReadOnly { access: ReadOnlyAccess }`
  - `WorkspaceWrite { ..., read_only_access: ReadOnlyAccess }`
- Preserved existing behavior by defaulting current construction paths
to `ReadOnlyAccess::FullAccess`.
- Threaded the new fields through sandbox policy consumers and call
sites across `core`, `tui`, `linux-sandbox`, `windows-sandbox`, and
related tests.
- Updated Seatbelt policy generation to honor restricted read roots by
emitting scoped read rules when full read access is not granted.
- Added fail-closed behavior on Linux and Windows backends when
restricted read access is requested but not yet implemented there
(`UnsupportedOperation`).
- Regenerated app-server protocol schema and TypeScript artifacts,
including `ReadOnlyAccess`.

## Compatibility / rollout

- Runtime behavior remains unchanged by default (`FullAccess`).
- API/schema changes are in place so future config wiring can enable
restricted read access without another policy-shape migration.

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

@@ -95,7 +95,7 @@ async fn user_turn_personality_none_does_not_add_update_message() -> anyhow::Res
             final_output_json_schema: None,
             cwd: test.cwd_path().to_path_buf(),
             approval_policy: test.config.approval_policy.value(),
-            sandbox_policy: SandboxPolicy::ReadOnly,
+            sandbox_policy: SandboxPolicy::new_read_only_policy(),
             model: test.session_configured.model.clone(),
             effort: test.config.model_reasoning_effort,
             summary: ReasoningSummary::Auto,
@@ -142,7 +142,7 @@ async fn config_personality_some_sets_instructions_template() -> anyhow::Result<
             final_output_json_schema: None,
             cwd: test.cwd_path().to_path_buf(),
             approval_policy: test.config.approval_policy.value(),
-            sandbox_policy: SandboxPolicy::ReadOnly,
+            sandbox_policy: SandboxPolicy::new_read_only_policy(),
             model: test.session_configured.model.clone(),
             effort: test.config.model_reasoning_effort,
             summary: ReasoningSummary::Auto,
@@ -196,7 +196,7 @@ async fn config_personality_none_sends_no_personality() -> anyhow::Result<()> {
             final_output_json_schema: None,
             cwd: test.cwd_path().to_path_buf(),
             approval_policy: test.config.approval_policy.value(),
-            sandbox_policy: SandboxPolicy::ReadOnly,
+            sandbox_policy: SandboxPolicy::new_read_only_policy(),
             model: test.session_configured.model.clone(),
             effort: test.config.model_reasoning_effort,
             summary: ReasoningSummary::Auto,
@@ -256,7 +256,7 @@ async fn default_personality_is_pragmatic_without_config_toml() -> anyhow::Resul
             final_output_json_schema: None,
             cwd: test.cwd_path().to_path_buf(),
             approval_policy: test.config.approval_policy.value(),
-            sandbox_policy: SandboxPolicy::ReadOnly,
+            sandbox_policy: SandboxPolicy::new_read_only_policy(),
             model: test.session_configured.model.clone(),
             effort: test.config.model_reasoning_effort,
             summary: ReasoningSummary::Auto,
@@ -304,7 +304,7 @@ async fn user_turn_personality_some_adds_update_message() -> anyhow::Result<()>
             final_output_json_schema: None,
             cwd: test.cwd_path().to_path_buf(),
             approval_policy: test.config.approval_policy.value(),
-            sandbox_policy: SandboxPolicy::ReadOnly,
+            sandbox_policy: SandboxPolicy::new_read_only_policy(),
             model: test.session_configured.model.clone(),
             effort: test.config.model_reasoning_effort,
             summary: ReasoningSummary::Auto,
@@ -338,7 +338,7 @@ async fn user_turn_personality_some_adds_update_message() -> anyhow::Result<()>
             final_output_json_schema: None,
             cwd: test.cwd_path().to_path_buf(),
             approval_policy: test.config.approval_policy.value(),
-            sandbox_policy: SandboxPolicy::ReadOnly,
+            sandbox_policy: SandboxPolicy::new_read_only_policy(),
             model: test.session_configured.model.clone(),
             effort: test.config.model_reasoning_effort,
             summary: ReasoningSummary::Auto,
@@ -401,7 +401,7 @@ async fn user_turn_personality_same_value_does_not_add_update_message() -> anyho
             final_output_json_schema: None,
             cwd: test.cwd_path().to_path_buf(),
             approval_policy: test.config.approval_policy.value(),
-            sandbox_policy: SandboxPolicy::ReadOnly,
+            sandbox_policy: SandboxPolicy::new_read_only_policy(),
             model: test.session_configured.model.clone(),
             effort: test.config.model_reasoning_effort,
             summary: ReasoningSummary::Auto,
@@ -435,7 +435,7 @@ async fn user_turn_personality_same_value_does_not_add_update_message() -> anyho
             final_output_json_schema: None,
             cwd: test.cwd_path().to_path_buf(),
             approval_policy: test.config.approval_policy.value(),
-            sandbox_policy: SandboxPolicy::ReadOnly,
+            sandbox_policy: SandboxPolicy::new_read_only_policy(),
             model: test.session_configured.model.clone(),
             effort: test.config.model_reasoning_effort,
             summary: ReasoningSummary::Auto,
@@ -508,7 +508,7 @@ async fn user_turn_personality_skips_if_feature_disabled() -> anyhow::Result<()>
             final_output_json_schema: None,
             cwd: test.cwd_path().to_path_buf(),
             approval_policy: test.config.approval_policy.value(),
-            sandbox_policy: SandboxPolicy::ReadOnly,
+            sandbox_policy: SandboxPolicy::new_read_only_policy(),
             model: test.session_configured.model.clone(),
             effort: test.config.model_reasoning_effort,
             summary: ReasoningSummary::Auto,
@@ -542,7 +542,7 @@ async fn user_turn_personality_skips_if_feature_disabled() -> anyhow::Result<()>
             final_output_json_schema: None,
             cwd: test.cwd_path().to_path_buf(),
             approval_policy: test.config.approval_policy.value(),
-            sandbox_policy: SandboxPolicy::ReadOnly,
+            sandbox_policy: SandboxPolicy::new_read_only_policy(),
             model: test.session_configured.model.clone(),
             effort: test.config.model_reasoning_effort,
             summary: ReasoningSummary::Auto,
@@ -654,7 +654,7 @@ async fn ignores_remote_personality_if_remote_models_disabled() -> anyhow::Resul
             final_output_json_schema: None,
             cwd: test.cwd_path().to_path_buf(),
             approval_policy: AskForApproval::Never,
-            sandbox_policy: SandboxPolicy::ReadOnly,
+            sandbox_policy: SandboxPolicy::new_read_only_policy(),
             model: remote_slug.to_string(),
             effort: test.config.model_reasoning_effort,
             summary: ReasoningSummary::Auto,
@@ -771,7 +771,7 @@ async fn remote_model_friendly_personality_instructions_with_feature() -> anyhow
             final_output_json_schema: None,
             cwd: test.cwd_path().to_path_buf(),
             approval_policy: AskForApproval::Never,
-            sandbox_policy: SandboxPolicy::ReadOnly,
+            sandbox_policy: SandboxPolicy::new_read_only_policy(),
             model: remote_slug.to_string(),
             effort: test.config.model_reasoning_effort,
             summary: ReasoningSummary::Auto,
@@ -886,7 +886,7 @@ async fn user_turn_personality_remote_model_template_includes_update_message() -
             final_output_json_schema: None,
             cwd: test.cwd_path().to_path_buf(),
             approval_policy: AskForApproval::Never,
-            sandbox_policy: SandboxPolicy::ReadOnly,
+            sandbox_policy: SandboxPolicy::new_read_only_policy(),
             model: remote_slug.to_string(),
             effort: test.config.model_reasoning_effort,
             summary: ReasoningSummary::Auto,
@@ -920,7 +920,7 @@ async fn user_turn_personality_remote_model_template_includes_update_message() -
             final_output_json_schema: None,
             cwd: test.cwd_path().to_path_buf(),
             approval_policy: AskForApproval::Never,
-            sandbox_policy: SandboxPolicy::ReadOnly,
+            sandbox_policy: SandboxPolicy::new_read_only_policy(),
             model: remote_slug.to_string(),
             effort: test.config.model_reasoning_effort,
             summary: ReasoningSummary::Auto,