diff --git a/codex-rs/core/src/next_prompt_suggestion.rs b/codex-rs/core/src/next_prompt_suggestion.rs
index 1edcdb653d..a544ce8568 100644
--- a/codex-rs/core/src/next_prompt_suggestion.rs
+++ b/codex-rs/core/src/next_prompt_suggestion.rs
@@ -35,6 +35,10 @@ use std::time::Duration;
 use std::time::Instant;
 use tokio_util::sync::CancellationToken;
 
+#[cfg(test)]
+#[path = "next_prompt_suggestion_tests.rs"]
+mod next_prompt_suggestion_tests;
+
 const NEXT_PROMPT_SUGGESTION_TOKEN_HEADROOM: i64 = 1_024;
 const NEXT_PROMPT_SUGGESTION_SAMPLE_TIMEOUT: Duration = Duration::from_secs(8);
 
@@ -264,14 +268,14 @@ fn history_matches_snapshot(history: &ContextManager, snapshot: HistorySnapshot)
 }
 
 async fn suggestion_prompt_fits_context_window(sess: &Session, turn_context: &TurnContext) -> bool {
-    let model_context_window = turn_context.model_context_window();
+    let Some(model_context_window) = turn_context.model_context_window() else {
+        tracing::debug!("next prompt suggestion skipped without model context window");
+        return false;
+    };
     let estimated_token_count = sess.get_estimated_token_count(turn_context).await;
-    if suggestion_prompt_has_headroom(estimated_token_count, model_context_window) {
+    if suggestion_prompt_has_headroom(estimated_token_count, Some(model_context_window)) {
         return true;
     }
-    let Some(model_context_window) = model_context_window else {
-        return true;
-    };
     let Some(estimated_token_count) = estimated_token_count else {
         return true;
     };
@@ -291,9 +295,10 @@ fn suggestion_prompt_has_headroom(
     estimated_token_count: Option<i64>,
     model_context_window: Option<i64>,
 ) -> bool {
-    let (Some(estimated_token_count), Some(model_context_window)) =
-        (estimated_token_count, model_context_window)
-    else {
+    let Some(model_context_window) = model_context_window else {
+        return false;
+    };
+    let Some(estimated_token_count) = estimated_token_count else {
         return true;
     };
     estimated_token_count
@@ -479,156 +484,3 @@ fn is_wrapped_meta(suggestion: &str) -> bool {
 fn starts_with_any(value: &str, prefixes: &[&str]) -> bool {
     prefixes.iter().any(|prefix| value.starts_with(prefix))
 }
-
-#[cfg(test)]
-mod tests {
-    use super::HistorySnapshot;
-    use super::filter_next_prompt_suggestion;
-    use super::has_unpaired_tool_flow;
-    use super::history_matches_snapshot;
-    use super::suggestion_prompt_has_headroom;
-    use crate::context_manager::ContextManager;
-    use codex_protocol::models::ContentItem;
-    use codex_protocol::models::FunctionCallOutputPayload;
-    use codex_protocol::models::ResponseItem;
-    use codex_utils_output_truncation::TruncationPolicy;
-    use pretty_assertions::assert_eq;
-
-    #[test]
-    fn filter_keeps_specific_prompt() {
-        assert_eq!(
-            filter_next_prompt_suggestion("run the tests"),
-            Some("run the tests".to_string())
-        );
-    }
-
-    #[test]
-    fn filter_keeps_allowed_single_word_prompt() {
-        assert_eq!(
-            filter_next_prompt_suggestion("commit"),
-            Some("commit".to_string())
-        );
-    }
-
-    #[test]
-    fn filter_keeps_code_identifier_prompt() {
-        assert_eq!(
-            filter_next_prompt_suggestion("set CODEX_HOME"),
-            Some("set CODEX_HOME".to_string())
-        );
-    }
-
-    #[test]
-    fn filter_keeps_dotted_file_prompt() {
-        assert_eq!(
-            filter_next_prompt_suggestion("update Cargo.toml"),
-            Some("update Cargo.toml".to_string())
-        );
-        assert_eq!(
-            filter_next_prompt_suggestion("open app-server/README.md"),
-            Some("open app-server/README.md".to_string())
-        );
-    }
-
-    #[test]
-    fn history_snapshot_detects_appends_and_rewrites() {
-        let mut history = ContextManager::new();
-        let snapshot = HistorySnapshot::from_history(&history);
-        assert!(history_matches_snapshot(&history, snapshot));
-
-        let item = ResponseItem::Message {
-            id: None,
-            role: "user".to_string(),
-            content: vec![ContentItem::InputText {
-                text: "next".to_string(),
-            }],
-            phase: None,
-        };
-        history.record_items([&item], TruncationPolicy::Tokens(10_000));
-        assert!(!history_matches_snapshot(&history, snapshot));
-
-        let appended_snapshot = HistorySnapshot::from_history(&history);
-        history.replace(history.raw_items().to_vec());
-        assert!(!history_matches_snapshot(&history, appended_snapshot));
-    }
-
-    #[test]
-    fn suggestion_prompt_skips_near_context_window() {
-        assert!(!suggestion_prompt_has_headroom(
-            /*estimated_token_count*/ Some(127_100),
-            /*model_context_window*/ Some(128_000)
-        ));
-    }
-
-    #[test]
-    fn incomplete_custom_tool_flow_is_suppressed() {
-        assert!(has_unpaired_tool_flow(&[ResponseItem::CustomToolCall {
-            id: None,
-            status: None,
-            call_id: "call-1".to_string(),
-            name: "exec".to_string(),
-            input: "{}".to_string(),
-        }]));
-    }
-
-    #[test]
-    fn completed_custom_tool_flow_is_allowed() {
-        assert!(!has_unpaired_tool_flow(&[
-            ResponseItem::CustomToolCall {
-                id: None,
-                status: None,
-                call_id: "call-1".to_string(),
-                name: "exec".to_string(),
-                input: "{}".to_string(),
-            },
-            ResponseItem::CustomToolCallOutput {
-                call_id: "call-1".to_string(),
-                name: Some("exec".to_string()),
-                output: FunctionCallOutputPayload::from_text("done".to_string()),
-            },
-        ]));
-    }
-
-    #[test]
-    fn server_tool_search_output_without_call_is_allowed() {
-        assert!(!has_unpaired_tool_flow(&[ResponseItem::ToolSearchOutput {
-            call_id: Some("call-1".to_string()),
-            status: "completed".to_string(),
-            execution: "server".to_string(),
-            tools: Vec::new(),
-        }]));
-    }
-
-    #[test]
-    fn client_tool_search_output_without_call_is_suppressed() {
-        assert!(has_unpaired_tool_flow(&[ResponseItem::ToolSearchOutput {
-            call_id: Some("call-1".to_string()),
-            status: "completed".to_string(),
-            execution: "client".to_string(),
-            tools: Vec::new(),
-        }]));
-    }
-
-    #[test]
-    fn filter_rejects_invalid_prompts() {
-        for suggestion in [
-            "",
-            "done",
-            "Suggestion: run the tests",
-            "(stay silent)",
-            "looks good",
-            "thanks",
-            "let me run tests",
-            "what about tests?",
-            "run tests.",
-            "run\ntests",
-            "continue with every possible next step in this project and explain every detail now",
-        ] {
-            assert_eq!(
-                filter_next_prompt_suggestion(suggestion),
-                None,
-                "expected {suggestion:?} to be filtered"
-            );
-        }
-    }
-}
diff --git a/codex-rs/core/src/next_prompt_suggestion_tests.rs b/codex-rs/core/src/next_prompt_suggestion_tests.rs
new file mode 100644
index 0000000000..7170aeeaf6
--- /dev/null
+++ b/codex-rs/core/src/next_prompt_suggestion_tests.rs
@@ -0,0 +1,157 @@
+use super::HistorySnapshot;
+use super::filter_next_prompt_suggestion;
+use super::has_unpaired_tool_flow;
+use super::history_matches_snapshot;
+use super::suggestion_prompt_has_headroom;
+use crate::context_manager::ContextManager;
+use codex_protocol::models::ContentItem;
+use codex_protocol::models::FunctionCallOutputPayload;
+use codex_protocol::models::ResponseItem;
+use codex_utils_output_truncation::TruncationPolicy;
+use pretty_assertions::assert_eq;
+
+#[test]
+fn filter_keeps_specific_prompt() {
+    assert_eq!(
+        filter_next_prompt_suggestion("run the tests"),
+        Some("run the tests".to_string())
+    );
+}
+
+#[test]
+fn filter_keeps_allowed_single_word_prompt() {
+    assert_eq!(
+        filter_next_prompt_suggestion("commit"),
+        Some("commit".to_string())
+    );
+}
+
+#[test]
+fn filter_keeps_code_identifier_prompt() {
+    assert_eq!(
+        filter_next_prompt_suggestion("set CODEX_HOME"),
+        Some("set CODEX_HOME".to_string())
+    );
+}
+
+#[test]
+fn filter_keeps_dotted_file_prompt() {
+    assert_eq!(
+        filter_next_prompt_suggestion("update Cargo.toml"),
+        Some("update Cargo.toml".to_string())
+    );
+    assert_eq!(
+        filter_next_prompt_suggestion("open app-server/README.md"),
+        Some("open app-server/README.md".to_string())
+    );
+}
+
+#[test]
+fn history_snapshot_detects_appends_and_rewrites() {
+    let mut history = ContextManager::new();
+    let snapshot = HistorySnapshot::from_history(&history);
+    assert!(history_matches_snapshot(&history, snapshot));
+
+    let item = ResponseItem::Message {
+        id: None,
+        role: "user".to_string(),
+        content: vec![ContentItem::InputText {
+            text: "next".to_string(),
+        }],
+        phase: None,
+    };
+    history.record_items([&item], TruncationPolicy::Tokens(10_000));
+    assert!(!history_matches_snapshot(&history, snapshot));
+
+    let appended_snapshot = HistorySnapshot::from_history(&history);
+    history.replace(history.raw_items().to_vec());
+    assert!(!history_matches_snapshot(&history, appended_snapshot));
+}
+
+#[test]
+fn suggestion_prompt_skips_without_context_window() {
+    assert!(!suggestion_prompt_has_headroom(
+        /*estimated_token_count*/ Some(10),
+        /*model_context_window*/ None,
+    ));
+}
+
+#[test]
+fn suggestion_prompt_skips_near_context_window() {
+    assert!(!suggestion_prompt_has_headroom(
+        /*estimated_token_count*/ Some(127_100),
+        /*model_context_window*/ Some(128_000)
+    ));
+}
+
+#[test]
+fn incomplete_custom_tool_flow_is_suppressed() {
+    assert!(has_unpaired_tool_flow(&[ResponseItem::CustomToolCall {
+        id: None,
+        status: None,
+        call_id: "call-1".to_string(),
+        name: "exec".to_string(),
+        input: "{}".to_string(),
+    }]));
+}
+
+#[test]
+fn completed_custom_tool_flow_is_allowed() {
+    assert!(!has_unpaired_tool_flow(&[
+        ResponseItem::CustomToolCall {
+            id: None,
+            status: None,
+            call_id: "call-1".to_string(),
+            name: "exec".to_string(),
+            input: "{}".to_string(),
+        },
+        ResponseItem::CustomToolCallOutput {
+            call_id: "call-1".to_string(),
+            name: Some("exec".to_string()),
+            output: FunctionCallOutputPayload::from_text("done".to_string()),
+        },
+    ]));
+}
+
+#[test]
+fn server_tool_search_output_without_call_is_allowed() {
+    assert!(!has_unpaired_tool_flow(&[ResponseItem::ToolSearchOutput {
+        call_id: Some("call-1".to_string()),
+        status: "completed".to_string(),
+        execution: "server".to_string(),
+        tools: Vec::new(),
+    }]));
+}
+
+#[test]
+fn client_tool_search_output_without_call_is_suppressed() {
+    assert!(has_unpaired_tool_flow(&[ResponseItem::ToolSearchOutput {
+        call_id: Some("call-1".to_string()),
+        status: "completed".to_string(),
+        execution: "client".to_string(),
+        tools: Vec::new(),
+    }]));
+}
+
+#[test]
+fn filter_rejects_invalid_prompts() {
+    for suggestion in [
+        "",
+        "done",
+        "Suggestion: run the tests",
+        "(stay silent)",
+        "looks good",
+        "thanks",
+        "let me run tests",
+        "what about tests?",
+        "run tests.",
+        "run\ntests",
+        "continue with every possible next step in this project and explain every detail now",
+    ] {
+        assert_eq!(
+            filter_next_prompt_suggestion(suggestion),
+            None,
+            "expected {suggestion:?} to be filtered"
+        );
+    }
+}