[codex-rs] Reliability pass on networking (#658)

We currently see a behavior that looks like this:
```
2025-04-25T16:52:24.552789Z  WARN codex_core::codex: stream disconnected - retrying turn (1/10 in 232ms)...
codex> event: BackgroundEvent { message: "stream error: stream disconnected before completion: Transport error: error decoding response body; retrying 1/10 in 232ms…" }
2025-04-25T16:52:54.789885Z  WARN codex_core::codex: stream disconnected - retrying turn (2/10 in 418ms)...
codex> event: BackgroundEvent { message: "stream error: stream disconnected before completion: Transport error: error decoding response body; retrying 2/10 in 418ms…" }
```

This PR contains a few different fixes that attempt to resolve/improve
this:
1. **Remove overall client timeout.** I think
[this](https://github.com/openai/codex/pull/658/files#diff-c39945d3c42f29b506ff54b7fa2be0795b06d7ad97f1bf33956f60e3c6f19c19L173)
is perhaps the big fix -- it looks to me like this was actually timing
out even if events were still coming through, and that was causing a
disconnect right in the middle of a healthy stream.
2. **Cap response sizes.** We were frequently sending MUCH larger
responses than the upstream typescript `codex`, and that was definitely
not helping. [Fix
here](https://github.com/openai/codex/pull/658/files#diff-d792bef59aa3ee8cb0cbad8b176dbfefe451c227ac89919da7c3e536a9d6cdc0R21-R26)
for that one.
3. **Much higher idle timeout.** Our idle timeout value was much lower
than typescript.
4. **Sub-linear backoff.** We were much too aggressively backing off,
[this](https://github.com/openai/codex/pull/658/files#diff-5d5959b95c6239e6188516da5c6b7eb78154cd9cfedfb9f753d30a7b6d6b8b06R30-R33)
makes it sub-exponential but maintains the jitter and such.

I was seeing that `stream error: stream disconnected` behavior
constantly, and anecdotally I can no longer reproduce. It feels much
snappier.

codex-rs/core/src/client.rs

@@ -28,7 +28,6 @@ use crate::flags::CODEX_RS_SSE_FIXTURE;
 use crate::flags::OPENAI_API_BASE;
 use crate::flags::OPENAI_REQUEST_MAX_RETRIES;
 use crate::flags::OPENAI_STREAM_IDLE_TIMEOUT_MS;
-use crate::flags::OPENAI_TIMEOUT_MS;
 use crate::models::ResponseInputItem;
 use crate::models::ResponseItem;
 use crate::util::backoff;
@@ -170,7 +169,6 @@ impl ModelClient {
                 .header("OpenAI-Beta", "responses=experimental")
                 .header(reqwest::header::ACCEPT, "text/event-stream")
                 .json(&payload)
-                .timeout(*OPENAI_TIMEOUT_MS)
                 .send()
                 .await;
             match res {

codex-rs/core/src/exec.rs

@@ -7,6 +7,7 @@ use std::time::Duration;
 use std::time::Instant;
 
 use serde::Deserialize;
+use tokio::io::AsyncRead;
 use tokio::io::AsyncReadExt;
 use tokio::io::BufReader;
 use tokio::process::Command;
@@ -17,9 +18,11 @@ use crate::error::Result;
 use crate::error::SandboxErr;
 use crate::protocol::SandboxPolicy;
 
-/// Maximum we keep for each stream (100 KiB).
-/// TODO(ragona) this should be reduced
-const MAX_STREAM_OUTPUT: usize = 100 * 1024;
+/// Maximum we send for each stream, which is either:
+/// - 10KiB OR
+/// - 256 lines
+const MAX_STREAM_OUTPUT: usize = 10 * 1024;
+const MAX_STREAM_OUTPUT_LINES: usize = 256;
 
 const DEFAULT_TIMEOUT_MS: u64 = 10_000;
 
@@ -222,10 +225,12 @@ pub async fn exec(
     let stdout_handle = tokio::spawn(read_capped(
         BufReader::new(child.stdout.take().expect("stdout is not piped")),
         MAX_STREAM_OUTPUT,
+        MAX_STREAM_OUTPUT_LINES,
     ));
     let stderr_handle = tokio::spawn(read_capped(
         BufReader::new(child.stderr.take().expect("stderr is not piped")),
         MAX_STREAM_OUTPUT,
+        MAX_STREAM_OUTPUT_LINES,
     ));
 
     let interrupted = ctrl_c.notified();
@@ -259,23 +264,41 @@ pub async fn exec(
     })
 }
 
-async fn read_capped<R: AsyncReadExt + Unpin>(
+async fn read_capped<R: AsyncRead + Unpin>(
     mut reader: R,
     max_output: usize,
+    max_lines: usize,
 ) -> io::Result<Vec<u8>> {
     let mut buf = Vec::with_capacity(max_output.min(8 * 1024));
     let mut tmp = [0u8; 8192];
 
+    let mut remaining_bytes = max_output;
+    let mut remaining_lines = max_lines;
+
     loop {
         let n = reader.read(&mut tmp).await?;
         if n == 0 {
             break;
         }
-        if buf.len() < max_output {
-            let remaining = max_output - buf.len();
-            buf.extend_from_slice(&tmp[..remaining.min(n)]);
+
+        // Copy into the buffer only while we still have byte and line budget.
+        if remaining_bytes > 0 && remaining_lines > 0 {
+            let mut copy_len = 0;
+            for &b in &tmp[..n] {
+                if remaining_bytes == 0 || remaining_lines == 0 {
+                    break;
+                }
+                copy_len += 1;
+                remaining_bytes -= 1;
+                if b == b'\n' {
+                    remaining_lines -= 1;
+                }
+            }
+            buf.extend_from_slice(&tmp[..copy_len]);
         }
+        // Continue reading to EOF to avoid back-pressure, but discard once caps are hit.
     }
+
     Ok(buf)
 }
 

codex-rs/core/src/flags.rs

@@ -9,16 +9,15 @@ env_flags! {
     pub OPENAI_DEFAULT_MODEL: &str = "o3";
     pub OPENAI_API_BASE: &str = "https://api.openai.com";
     pub OPENAI_API_KEY: Option<&str> = None;
-    pub OPENAI_TIMEOUT_MS: Duration = Duration::from_millis(30_000), |value| {
+    pub OPENAI_TIMEOUT_MS: Duration = Duration::from_millis(300_000), |value| {
         value.parse().map(Duration::from_millis)
     };
     pub OPENAI_REQUEST_MAX_RETRIES: u64 = 4;
     pub OPENAI_STREAM_MAX_RETRIES: u64 = 10;
 
-    /// Maximum idle time (no SSE events received) before the stream is treated as
-    /// disconnected and retried by the agent. The default of 75 s is slightly
-    /// above OpenAI’s documented 60 s load‑balancer timeout.
-    pub OPENAI_STREAM_IDLE_TIMEOUT_MS: Duration = Duration::from_millis(75_000), |value| {
+    // We generally don't want to disconnect; this updates the timeout to be five minutes
+    // which matches the upstream typescript codex impl.
+    pub OPENAI_STREAM_IDLE_TIMEOUT_MS: Duration = Duration::from_millis(300_000), |value| {
         value.parse().map(Duration::from_millis)
     };
 

codex-rs/core/src/util.rs

@@ -5,6 +5,9 @@ use rand::Rng;
 use tokio::sync::Notify;
 use tracing::debug;
 
+const INITIAL_DELAY_MS: u64 = 200;
+const BACKOFF_FACTOR: f64 = 1.3;
+
 /// Make a CancellationToken that is fulfilled when SIGINT occurs.
 pub fn notify_on_sigint() -> Arc<Notify> {
     let notify = Arc::new(Notify::new());
@@ -23,12 +26,11 @@ pub fn notify_on_sigint() -> Arc<Notify> {
     notify
 }
 
-/// Default exponential back‑off schedule: 200ms → 400ms → 800ms → 1600ms.
 pub(crate) fn backoff(attempt: u64) -> Duration {
-    let base_delay_ms = 200u64 * (1u64 << (attempt - 1));
-    let jitter = rand::rng().random_range(0.8..1.2);
-    let delay_ms = (base_delay_ms as f64 * jitter) as u64;
-    Duration::from_millis(delay_ms)
+    let exp = BACKOFF_FACTOR.powi(attempt.saturating_sub(1) as i32);
+    let base = (INITIAL_DELAY_MS as f64 * exp) as u64;
+    let jitter = rand::rng().random_range(0.9..1.1);
+    Duration::from_millis((base as f64 * jitter) as u64)
 }
 
 /// Return `true` if the current working directory is inside a Git repository.