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/src/session/turn.rs

@@ -95,9 +95,7 @@ use codex_protocol::protocol::ReasoningRawContentDeltaEvent;
 use codex_protocol::protocol::TurnDiffEvent;
 use codex_protocol::protocol::WarningEvent;
 use codex_protocol::user_input::UserInput;
-use codex_tools::ResponsesApiNamespaceTool;
 use codex_tools::ToolName;
-use codex_tools::ToolSpec;
 use codex_tools::filter_tool_suggest_discoverable_tools_for_client;
 use codex_utils_stream_parser::AssistantTextChunk;
 use codex_utils_stream_parser::AssistantTextStreamParser;
@@ -946,25 +944,9 @@ pub(crate) fn build_prompt(
     turn_context: &TurnContext,
     base_instructions: BaseInstructions,
 ) -> Prompt {
-    let deferred_dynamic_tools = turn_context
-        .dynamic_tools
-        .iter()
-        .filter(|tool| tool.defer_loading)
-        .map(|tool| ToolName::new(tool.namespace.clone(), tool.name.clone()))
-        .collect::<HashSet<_>>();
-    let tools = if deferred_dynamic_tools.is_empty() {
-        router.model_visible_specs()
-    } else {
-        router
-            .model_visible_specs()
-            .into_iter()
-            .filter_map(|spec| filter_deferred_dynamic_tool_spec(spec, &deferred_dynamic_tools))
-            .collect()
-    };
-
     Prompt {
         input,
-        tools,
+        tools: router.model_visible_specs(),
         parallel_tool_calls: turn_context.model_info.supports_parallel_tool_calls,
         base_instructions,
         personality: turn_context.personality,
@@ -975,35 +957,6 @@ pub(crate) fn build_prompt(
     }
 }
 
-fn filter_deferred_dynamic_tool_spec(
-    spec: ToolSpec,
-    deferred_dynamic_tools: &HashSet<ToolName>,
-) -> Option<ToolSpec> {
-    match spec {
-        ToolSpec::Function(tool) => {
-            if deferred_dynamic_tools.contains(&ToolName::plain(tool.name.as_str())) {
-                None
-            } else {
-                Some(ToolSpec::Function(tool))
-            }
-        }
-        ToolSpec::Namespace(mut namespace) => {
-            let namespace_name = namespace.name.clone();
-            namespace.tools.retain(|tool| match tool {
-                ResponsesApiNamespaceTool::Function(tool) => !deferred_dynamic_tools.contains(
-                    &ToolName::namespaced(namespace_name.as_str(), tool.name.as_str()),
-                ),
-            });
-            if namespace.tools.is_empty() {
-                None
-            } else {
-                Some(ToolSpec::Namespace(namespace))
-            }
-        }
-        spec => Some(spec),
-    }
-}
-
 #[allow(clippy::too_many_arguments)]
 #[instrument(level = "trace",
     skip_all,

codex-rs/core/src/tools/router.rs

@@ -71,23 +71,26 @@ impl ToolRouter {
             dynamic_tools,
         );
         let (specs, registry) = builder.build();
-        let model_visible_specs = if config.code_mode_only_enabled {
-            specs
-                .iter()
-                .filter_map(|configured_tool| {
-                    if !codex_code_mode::is_code_mode_nested_tool(configured_tool.name()) {
-                        Some(configured_tool.spec.clone())
-                    } else {
-                        None
-                    }
-                })
-                .collect()
-        } else {
-            specs
-                .iter()
-                .map(|configured_tool| configured_tool.spec.clone())
-                .collect()
-        };
+        let deferred_dynamic_tools = dynamic_tools
+            .iter()
+            .filter(|tool| tool.defer_loading)
+            .map(|tool| ToolName::new(tool.namespace.clone(), tool.name.clone()))
+            .collect::<HashSet<_>>();
+        let model_visible_specs = specs
+            .iter()
+            .filter_map(|configured_tool| {
+                if config.code_mode_only_enabled
+                    && codex_code_mode::is_code_mode_nested_tool(configured_tool.name())
+                {
+                    return None;
+                }
+
+                filter_deferred_dynamic_tool_spec(
+                    configured_tool.spec.clone(),
+                    &deferred_dynamic_tools,
+                )
+            })
+            .collect();
 
         Self {
             registry,
@@ -293,6 +296,39 @@ impl ToolRouter {
         self.registry.dispatch_any(invocation).await
     }
 }
+
+fn filter_deferred_dynamic_tool_spec(
+    spec: ToolSpec,
+    deferred_dynamic_tools: &HashSet<ToolName>,
+) -> Option<ToolSpec> {
+    if deferred_dynamic_tools.is_empty() {
+        return Some(spec);
+    }
+
+    match spec {
+        ToolSpec::Function(tool) => {
+            if deferred_dynamic_tools.contains(&ToolName::plain(tool.name.as_str())) {
+                None
+            } else {
+                Some(ToolSpec::Function(tool))
+            }
+        }
+        ToolSpec::Namespace(mut namespace) => {
+            let namespace_name = namespace.name.clone();
+            namespace.tools.retain(|tool| match tool {
+                ResponsesApiNamespaceTool::Function(tool) => !deferred_dynamic_tools.contains(
+                    &ToolName::namespaced(namespace_name.as_str(), tool.name.as_str()),
+                ),
+            });
+            if namespace.tools.is_empty() {
+                None
+            } else {
+                Some(ToolSpec::Namespace(namespace))
+            }
+        }
+        spec => Some(spec),
+    }
+}
 #[cfg(test)]
 #[path = "router_tests.rs"]
 mod tests;

codex-rs/core/src/tools/router_tests.rs

@@ -3,8 +3,13 @@ use std::sync::Arc;
 
 use crate::session::tests::make_session_and_context;
 use crate::tools::context::ToolPayload;
+use codex_protocol::dynamic_tools::DynamicToolSpec;
 use codex_protocol::models::ResponseItem;
+use codex_tools::ResponsesApiNamespaceTool;
 use codex_tools::ToolName;
+use codex_tools::ToolSpec;
+use pretty_assertions::assert_eq;
+use serde_json::json;
 
 use super::ToolCall;
 use super::ToolRouter;
@@ -133,3 +138,86 @@ async fn mcp_parallel_support_uses_exact_payload_server() -> anyhow::Result<()>
 
     Ok(())
 }
+
+#[tokio::test]
+async fn model_visible_specs_filter_deferred_dynamic_tools() -> anyhow::Result<()> {
+    let (_, turn) = make_session_and_context().await;
+    let hidden_tool = "hidden_dynamic_tool";
+    let visible_tool = "visible_dynamic_tool";
+    let dynamic_tools = vec![
+        DynamicToolSpec {
+            namespace: Some("codex_app".to_string()),
+            name: hidden_tool.to_string(),
+            description: "Hidden until discovered.".to_string(),
+            input_schema: json!({
+                "type": "object",
+                "properties": {},
+                "additionalProperties": false,
+            }),
+            defer_loading: true,
+        },
+        DynamicToolSpec {
+            namespace: Some("codex_app".to_string()),
+            name: visible_tool.to_string(),
+            description: "Visible immediately.".to_string(),
+            input_schema: json!({
+                "type": "object",
+                "properties": {},
+                "additionalProperties": false,
+            }),
+            defer_loading: false,
+        },
+    ];
+
+    let router = ToolRouter::from_config(
+        &turn.tools_config,
+        ToolRouterParams {
+            deferred_mcp_tools: None,
+            mcp_tools: None,
+            unavailable_called_tools: Vec::new(),
+            parallel_mcp_server_names: HashSet::new(),
+            discoverable_tools: None,
+            dynamic_tools: &dynamic_tools,
+        },
+    );
+
+    assert!(
+        router
+            .find_spec(&ToolName::namespaced("codex_app", hidden_tool))
+            .is_some()
+    );
+    assert_eq!(
+        namespace_function_names(&router.specs(), "codex_app"),
+        vec![hidden_tool.to_string(), visible_tool.to_string()]
+    );
+    assert_eq!(
+        namespace_function_names(&router.model_visible_specs(), "codex_app"),
+        vec![visible_tool.to_string()]
+    );
+
+    Ok(())
+}
+
+fn namespace_function_names(specs: &[ToolSpec], namespace_name: &str) -> Vec<String> {
+    specs
+        .iter()
+        .find_map(|spec| match spec {
+            ToolSpec::Namespace(namespace) if namespace.name == namespace_name => Some(
+                namespace
+                    .tools
+                    .iter()
+                    .map(|tool| match tool {
+                        ResponsesApiNamespaceTool::Function(tool) => tool.name.clone(),
+                    })
+                    .collect(),
+            ),
+            ToolSpec::Function(_)
+            | ToolSpec::Freeform(_)
+            | ToolSpec::ToolSearch { .. }
+            | ToolSpec::LocalShell {}
+            | ToolSpec::ImageGeneration { .. }
+            | ToolSpec::WebSearch { .. }
+            | ToolSpec::Namespace(_) => None,
+        })
+        .unwrap_or_default()
+}