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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[//]: # (BEGIN SAPLING FOOTER)
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* #7112
* __->__ #7122

codex-rs/linux-sandbox/tests/suite/landlock.rs

@@ -3,7 +3,6 @@ use codex_core::config::types::ShellEnvironmentPolicy;
 use codex_core::error::CodexErr;
 use codex_core::error::SandboxErr;
 use codex_core::exec::ExecParams;
-use codex_core::exec::SandboxType;
 use codex_core::exec::process_exec_tool_call;
 use codex_core::exec_env::create_env;
 use codex_core::protocol::SandboxPolicy;
@@ -60,7 +59,6 @@ async fn run_cmd(cmd: &[&str], writable_roots: &[PathBuf], timeout_ms: u64) {
     let codex_linux_sandbox_exe = Some(PathBuf::from(sandbox_program));
     let res = process_exec_tool_call(
         params,
-        SandboxType::LinuxSeccomp,
         &sandbox_policy,
         sandbox_cwd.as_path(),
         &codex_linux_sandbox_exe,
@@ -155,7 +153,6 @@ async fn assert_network_blocked(cmd: &[&str]) {
     let codex_linux_sandbox_exe: Option<PathBuf> = Some(PathBuf::from(sandbox_program));
     let result = process_exec_tool_call(
         params,
-        SandboxType::LinuxSeccomp,
         &sandbox_policy,
         sandbox_cwd.as_path(),
         &codex_linux_sandbox_exe,