Remove deterministic_process_ids feature to avoid duplicate codex-core builds (#11393)

## Why

`codex-core` enabled `deterministic_process_ids` through a self
dev-dependency.
That forced a second feature-resolved build of the same crate, which
increased
compile time and test latency.

## What Changed

- Removed the `deterministic_process_ids` feature from
`codex-rs/core/Cargo.toml`.
- Removed the self dev-dependency on `codex-core` that enabled that
feature.
- Removed the Bazel `deterministic_process_ids` crate feature for
`codex-core`.
- Added a test-only `AtomicBool` override in unified exec process-id
allocation.
- Added a test-support setter for that override and re-exported it from
`codex-core`.
- Enabled deterministic process IDs in integration tests via
`core_test_support` ctor.

## Behavior

- Production behavior remains random process IDs.
- Unit tests remain deterministic via `cfg(test)`.
- Integration tests remain deterministic via explicit test-support
initialization.

## Validation

- `just fmt`
- `cargo test -p codex-core unified_exec::`
- `cargo test -p codex-core --test all unified_exec -- --test-threads=1`
- `cargo tree -p codex-core -e features` (verified the removed feature
path)

codex-rs/core/src/unified_exec/mod.rs

@@ -42,6 +42,11 @@ mod head_tail_buffer;
 mod process;
 mod process_manager;
 
+#[cfg(any(test, feature = "test-support"))]
+pub fn set_deterministic_process_ids_for_tests(enabled: bool) {
+    process_manager::set_deterministic_process_ids_for_tests(enabled);
+}
+
 pub(crate) use errors::UnifiedExecError;
 pub(crate) use process::UnifiedExecProcess;
 

codex-rs/core/src/unified_exec/process_manager.rs

@@ -5,6 +5,7 @@ use std::collections::HashSet;
 use std::path::PathBuf;
 use std::sync::Arc;
 use std::sync::atomic::AtomicBool;
+use std::sync::atomic::Ordering;
 use tokio::sync::Notify;
 use tokio::sync::mpsc;
 use tokio::time::Duration;
@@ -61,6 +62,32 @@ const UNIFIED_EXEC_ENV: [(&str, &str); 10] = [
     ("CODEX_CI", "1"),
 ];
 
+#[cfg(any(test, feature = "test-support"))]
+/// Test-only override for deterministic unified exec process IDs.
+///
+/// In production builds this value should remain at its default (`false`) and
+/// must not be toggled.
+static FORCE_DETERMINISTIC_PROCESS_IDS: AtomicBool = AtomicBool::new(false);
+
+#[cfg(any(test, feature = "test-support"))]
+pub(super) fn set_deterministic_process_ids_for_tests(enabled: bool) {
+    FORCE_DETERMINISTIC_PROCESS_IDS.store(enabled, Ordering::Relaxed);
+}
+
+#[cfg(any(test, feature = "test-support"))]
+fn deterministic_process_ids_forced_for_tests() -> bool {
+    FORCE_DETERMINISTIC_PROCESS_IDS.load(Ordering::Relaxed)
+}
+
+#[cfg(not(any(test, feature = "test-support")))]
+fn deterministic_process_ids_forced_for_tests() -> bool {
+    false
+}
+
+fn should_use_deterministic_process_ids() -> bool {
+    cfg!(test) || deterministic_process_ids_forced_for_tests()
+}
+
 fn apply_unified_exec_env(mut env: HashMap<String, String>) -> HashMap<String, String> {
     for (key, value) in UNIFIED_EXEC_ENV {
         env.insert(key.to_string(), value.to_string());
@@ -85,10 +112,7 @@ impl UnifiedExecProcessManager {
         loop {
             let mut store = self.process_store.lock().await;
 
-            let process_id = if !cfg!(test) && !cfg!(feature = "deterministic_process_ids") {
-                // production mode → random
-                rand::rng().random_range(1_000..100_000).to_string()
-            } else {
+            let process_id = if should_use_deterministic_process_ids() {
                 // test or deterministic mode
                 let next = store
                     .reserved_process_ids
@@ -99,6 +123,9 @@ impl UnifiedExecProcessManager {
                     .unwrap_or(1000);
 
                 next.to_string()
+            } else {
+                // production mode → random
+                rand::rng().random_range(1_000..100_000).to_string()
             };
 
             if store.reserved_process_ids.contains(&process_id) {