refactor: inline sandbox type lookup in process_exec_tool_call (#7122)

`process_exec_tool_call()` was taking `SandboxType` as a param, but in
practice, the only place it was constructed was in
`codex_message_processor.rs` where it was derived from the other
`sandbox_policy` param, so this PR inlines the logic that decides the
`SandboxType` into `process_exec_tool_call()`.



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* #7112
* __->__ #7122

codex-rs/exec-server/src/posix/escalate_server.rs

@@ -8,9 +8,7 @@ use std::time::Duration;
 use anyhow::Context as _;
 use path_absolutize::Absolutize as _;
 
-use codex_core::exec::SandboxType;
 use codex_core::exec::process_exec_tool_call;
-use codex_core::get_platform_sandbox;
 use codex_core::protocol::SandboxPolicy;
 use tokio::process::Command;
 use tokio_util::sync::CancellationToken;
@@ -96,7 +94,6 @@ impl EscalateServer {
                 justification: None,
                 arg0: None,
             },
-            get_platform_sandbox().unwrap_or(SandboxType::None),
             &sandbox_policy,
             &sandbox_cwd,
             &None,