fix: filter dynamic deferred tools from model_visible_specs (#19771)

fixes #19486

### Problem
Right now dynamic deferred tools are filtered at normal-turn prompt
building time, rather than upstream while building the `ToolRouter`
itself. This causes issues because dynamic deferred tools are then
wrongly included in the router's `model_visible_specs`, which is what
the compaction request-building flow relies on.

### Fix
Move the dynamic deferred tool filtering to `ToolRouter` creation time
to solve this problem for every request that relies on `ToolRouter` for
`model_visible_specs`, which solves the issue generically.

### Tests
Added unit + integration tests to ensure dynamic deferred tools are
omitted from `model_visible_specs` and compaction request respectively.

Tested against live `/compact` endpoint; raw deferred dynamic tools
without `tool_search` returned `400` (current bug), while the filtered
payload (this fix) returns `200`.

codex-rs/core/tests/suite/compact_remote.rs

@@ -6,6 +6,7 @@ use std::path::PathBuf;
 use anyhow::Result;
 use codex_core::compact::SUMMARY_PREFIX;
 use codex_login::CodexAuth;
+use codex_protocol::dynamic_tools::DynamicToolSpec;
 use codex_protocol::items::TurnItem;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::ResponseItem;
@@ -36,6 +37,7 @@ use core_test_support::wait_for_event;
 use core_test_support::wait_for_event_match;
 use core_test_support::wait_for_event_with_timeout;
 use pretty_assertions::assert_eq;
+use serde_json::Value;
 use serde_json::json;
 use tokio::time::Duration;
 use wiremock::ResponseTemplate;
@@ -55,6 +57,53 @@ fn estimate_compact_payload_tokens(request: &responses::ResponsesRequest) -> i64
         .saturating_add(approx_token_count(&request.instructions_text()))
 }
 
+fn assert_tools_payload_does_not_defer(body: &Value) {
+    if let Some(tools) = body.get("tools") {
+        assert!(
+            !contains_defer_loading(tools),
+            "model-visible tools should not include deferred declarations: {tools}"
+        );
+    }
+}
+
+fn namespace_child_tool_names(body: &Value, namespace: &str) -> Vec<String> {
+    body.get("tools")
+        .and_then(Value::as_array)
+        .and_then(|tools| {
+            tools.iter().find_map(|tool| {
+                if tool.get("type").and_then(Value::as_str) == Some("namespace")
+                    && tool.get("name").and_then(Value::as_str) == Some(namespace)
+                {
+                    tool.get("tools").and_then(Value::as_array).map(|children| {
+                        children
+                            .iter()
+                            .filter_map(|child| {
+                                child
+                                    .get("name")
+                                    .and_then(Value::as_str)
+                                    .map(str::to_string)
+                            })
+                            .collect()
+                    })
+                } else {
+                    None
+                }
+            })
+        })
+        .unwrap_or_default()
+}
+
+fn contains_defer_loading(value: &Value) -> bool {
+    match value {
+        Value::Object(map) => {
+            map.get("defer_loading").and_then(Value::as_bool) == Some(true)
+                || map.values().any(contains_defer_loading)
+        }
+        Value::Array(values) => values.iter().any(contains_defer_loading),
+        Value::Null | Value::Bool(_) | Value::Number(_) | Value::String(_) => false,
+    }
+}
+
 const PRETURN_CONTEXT_DIFF_CWD: &str = "/tmp/PRETURN_CONTEXT_DIFF_CWD";
 const DUMMY_FUNCTION_NAME: &str = "test_tool";
 const REMOTE_COMPACT_TURN_COMPLETE_TIMEOUT: Duration = Duration::from_secs(30);
@@ -358,6 +407,100 @@ async fn remote_compact_replaces_history_for_followups() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn remote_compact_filters_deferred_dynamic_tools() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = responses::start_mock_server().await;
+    let mut builder = test_codex().with_auth(CodexAuth::create_dummy_chatgpt_auth_for_testing());
+    let mut test = builder.build(&server).await?;
+    let hidden_tool = "hidden_dynamic_tool";
+    let visible_tool = "visible_dynamic_tool";
+    let input_schema = json!({
+        "type": "object",
+        "properties": {},
+        "additionalProperties": false,
+    });
+    let dynamic_tools = vec![
+        DynamicToolSpec {
+            namespace: Some("codex_app".to_string()),
+            name: hidden_tool.to_string(),
+            description: "Hidden until discovered.".to_string(),
+            input_schema: input_schema.clone(),
+            defer_loading: true,
+        },
+        DynamicToolSpec {
+            namespace: Some("codex_app".to_string()),
+            name: visible_tool.to_string(),
+            description: "Visible immediately.".to_string(),
+            input_schema,
+            defer_loading: false,
+        },
+    ];
+    let new_thread = test
+        .thread_manager
+        .start_thread_with_tools(
+            test.config.clone(),
+            dynamic_tools,
+            /*persist_extended_history*/ false,
+        )
+        .await?;
+    test.codex = new_thread.thread;
+    test.session_configured = new_thread.session_configured;
+    let codex = test.codex.clone();
+
+    let responses_mock = mount_sse_once(
+        &server,
+        sse(vec![
+            responses::ev_assistant_message("m1", "FIRST_REMOTE_REPLY"),
+            responses::ev_completed("resp-1"),
+        ]),
+    )
+    .await;
+    let compact_mock = responses::mount_compact_json_once(
+        &server,
+        serde_json::json!({
+            "output": compacted_summary_only_output("compact summary"),
+        }),
+    )
+    .await;
+
+    codex
+        .submit(Op::UserInput {
+            environments: None,
+            items: vec![UserInput::Text {
+                text: "hello remote compact".into(),
+                text_elements: Vec::new(),
+            }],
+            final_output_json_schema: None,
+            responsesapi_client_metadata: None,
+        })
+        .await?;
+    wait_for_turn_complete(&codex).await;
+
+    codex.submit(Op::Compact).await?;
+    wait_for_turn_complete(&codex).await;
+
+    let first_response_body = responses_mock.single_request().body_json();
+    let compact_body = compact_mock.single_request().body_json();
+    assert_eq!(
+        compact_body["tools"], first_response_body["tools"],
+        "compact requests should send the same model-visible tools payload as /v1/responses"
+    );
+    assert_tools_payload_does_not_defer(&first_response_body);
+    assert_tools_payload_does_not_defer(&compact_body);
+    assert_eq!(
+        namespace_child_tool_names(&first_response_body, "codex_app"),
+        vec![visible_tool.to_string()]
+    );
+    assert_eq!(
+        namespace_child_tool_names(&compact_body, "codex_app"),
+        vec![visible_tool.to_string()]
+    );
+
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn remote_compact_runs_automatically() -> Result<()> {
     skip_if_no_network!(Ok(()));