Scope MCP sandbox metadata to server environment (#28914)

Scope MCP sandbox metadata to the MCP server's owning environment.

Previously, `codex/sandbox-state-meta` always used the turn's primary
cwd and rebuilt a legacy sandbox policy from that cwd. That can be wrong
for MCP servers owned by a different execution environment.

This now sends the owning environment cwd as a `file:` URI in
`sandboxCwd`, keeps `permissionProfile` as the permission source of
truth, and omits sandbox-state metadata when a non-default server
environment is not selected for the turn. Local/default MCP servers keep
the existing fallback cwd behavior.

Tests:
- `just fmt`
- `just bazel-lock-update`
- `just bazel-lock-check`
- `just test -p codex-mcp`
- `just test -p codex-core mcp_sandbox_cwd`
- `cargo build -p codex-rmcp-client --bin test_stdio_server`
- `just test -p codex-core
stdio_mcp_tool_call_includes_sandbox_state_meta`

codex-rs/codex-mcp/src/runtime.rs

@@ -12,7 +12,7 @@ use std::time::Duration;
 use codex_exec_server::Environment;
 use codex_exec_server::EnvironmentManager;
 use codex_protocol::models::PermissionProfile;
-use codex_protocol::protocol::SandboxPolicy;
+use codex_utils_path_uri::PathUri;
 
 use serde::Deserialize;
 use serde::Serialize;
@@ -22,9 +22,8 @@ use serde::Serialize;
 pub struct SandboxState {
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub permission_profile: Option<PermissionProfile>,
-    pub sandbox_policy: SandboxPolicy,
     pub codex_linux_sandbox_exe: Option<PathBuf>,
-    pub sandbox_cwd: PathBuf,
+    pub sandbox_cwd: PathUri,
     #[serde(default)]
     pub use_legacy_landlock: bool,
 }