feat: add ZDR support to Rust implementation (#642)

This adds support for the `--disable-response-storage` flag across our
multiple Rust CLIs to support customers who have opted into Zero-Data
Retention (ZDR). The analogous changes to the TypeScript CLI were:

* https://github.com/openai/codex/pull/481
* https://github.com/openai/codex/pull/543

For a client using ZDR, `previous_response_id` will never be available,
so the `input` field of an API request must include the full transcript
of the conversation thus far. As such, this PR changes the type of
`Prompt.input` from `Vec<ResponseInputItem>` to `Vec<ResponseItem>`.

Practically speaking, `ResponseItem` was effectively a "superset" of
`ResponseInputItem` already. The main difference for us is that
`ResponseItem` includes the `FunctionCall` variant that we have to
include as part of the conversation history in the ZDR case.

Another key change in this PR is modifying `try_run_turn()` so that it
returns the `Vec<ResponseItem>` for the turn in addition to the
`Vec<ResponseInputItem>` produced by `try_run_turn()`. This is because
the caller of `run_turn()` needs to record the `Vec<ResponseItem>` when
ZDR is enabled.

To that end, this PR introduces `ZdrTranscript` (and adds
`zdr_transcript: Option<ZdrTranscript>` to `struct State` in `codex.rs`)
to take responsibility for maintaining the conversation transcript in
the ZDR case.

codex-rs/repl/src/cli.rs

@@ -50,6 +50,10 @@ pub struct Cli {
     #[arg(long, action = ArgAction::SetTrue, default_value_t = false)]
     pub allow_no_git_exec: bool,
 
+    /// Disable server‑side response storage (sends the full conversation context with every request)
+    #[arg(long = "disable-response-storage", default_value_t = false)]
+    pub disable_response_storage: bool,
+
     /// Record submissions into file as JSON
     #[arg(short = 'S', long)]
     pub record_submissions: Option<String>,

codex-rs/repl/src/lib.rs

@@ -97,6 +97,7 @@ async fn codex_main(mut cli: Cli, cfg: Config, ctrl_c: Arc<Notify>) -> anyhow::R
             instructions: cfg.instructions,
             approval_policy: cli.approval_policy.into(),
             sandbox_policy: cli.sandbox_policy.into(),
+            disable_response_storage: cli.disable_response_storage,
         },
     };