Simplify tool executor and registry plumbing (#22636)

## Why

The tool runtime path still had a typed output associated type on
`ToolExecutor`, plus a core-only `RegisteredTool` adapter and
extension-only executor aliases. That made every new shared tool runtime
carry extra adapter plumbing before it could participate in core
dispatch, extension tools, hook payloads, telemetry, and model-visible
spec generation.

This PR moves output erasure to the shared executor boundary so core and
extension tools can use the same execution contract directly.

## What Changed

- Changed `codex_tools::ToolExecutor` to return `Box<dyn ToolOutput>`
instead of an associated `Output` type.
- Removed the extension-specific `ExtensionToolExecutor` /
`ExtensionToolOutput` aliases and exposed `ToolExecutor<ToolCall>` plus
`ToolOutput` through `codex-extension-api`.
- Reworked core tool registration around `CoreToolRuntime` and
`ToolRegistry::from_tools`, removing the extra `RegisteredTool` /
`ToolRegistryBuilder` layer.
- Consolidated model-visible spec planning and registry construction in
`core/src/tools/spec_plan.rs`, including deferred tool search and
code-mode-only filtering.
- Added `ToolOutput` helpers for post-tool-use hook ids and inputs so
MCP, unified exec, extension, and other boxed outputs preserve the same
hook payload behavior.
- Updated core handlers, memories tools, and the related
registry/spec/router tests to use the simplified contract.

## Test Coverage

- Updated coverage for tool spec planning, registry lookup, deferred
tool search registration, extension tool routing, post-tool-use hook
payloads, dispatch tracing, guardian output extraction, and memories
extension tool execution.

codex-rs/ext/memories/src/extension.rs

@@ -63,7 +63,7 @@ impl ToolContributor for MemoriesExtension {
         &self,
         _session_store: &ExtensionData,
         thread_store: &ExtensionData,
-    ) -> Vec<Arc<dyn codex_extension_api::ExtensionToolExecutor>> {
+    ) -> Vec<Arc<dyn codex_extension_api::ToolExecutor<codex_extension_api::ToolCall>>> {
         let Some(config) = thread_store.get::<MemoriesExtensionConfig>() else {
             return Vec::new();
         };

codex-rs/ext/memories/src/tests.rs

@@ -3,10 +3,10 @@ use std::sync::Arc;
 
 use codex_extension_api::ContextContributor;
 use codex_extension_api::ExtensionData;
-use codex_extension_api::ExtensionToolExecutor;
 use codex_extension_api::PromptSlot;
 use codex_extension_api::ToolCall;
 use codex_extension_api::ToolContributor;
+use codex_extension_api::ToolExecutor;
 use codex_extension_api::ToolName;
 use codex_extension_api::ToolPayload;
 use codex_tools::ToolOutput;
@@ -290,20 +290,23 @@ async fn search_tool_rejects_legacy_single_query() {
         .to_string(),
     };
 
-    let err = tool
+    let result = tool
         .handle(ToolCall {
             call_id: "call-1".to_string(),
             tool_name: memory_tool_name(crate::SEARCH_TOOL_NAME),
             payload,
         })
-        .await
-        .expect_err("legacy query field should be rejected");
+        .await;
+    let err = match result {
+        Ok(_) => panic!("legacy query field should be rejected"),
+        Err(err) => err,
+    };
 
     assert!(err.to_string().contains("unknown field"));
     assert!(err.to_string().contains("query"));
 }
 
-fn memory_tool(memory_root: &Path, tool_name: &str) -> Arc<dyn ExtensionToolExecutor> {
+fn memory_tool(memory_root: &Path, tool_name: &str) -> Arc<dyn ToolExecutor<ToolCall>> {
     let expected_tool_name = memory_tool_name(tool_name);
     crate::tools::memory_tools(LocalMemoriesBackend::from_memory_root(memory_root))
         .into_iter()

codex-rs/ext/memories/src/tools/list.rs

@@ -39,8 +39,6 @@ impl<B> ToolExecutor<ToolCall> for ListTool<B>
 where
     B: MemoriesBackend,
 {
-    type Output = JsonToolOutput;
-
     fn tool_name(&self) -> ToolName {
         memory_tool_name(LIST_TOOL_NAME)
     }
@@ -55,7 +53,8 @@ where
     async fn handle(
         &self,
         call: ToolCall,
-    ) -> Result<Self::Output, codex_extension_api::FunctionCallError> {
+    ) -> Result<Box<dyn codex_extension_api::ToolOutput>, codex_extension_api::FunctionCallError>
+    {
         let backend = self.backend.clone();
         let args: ListArgs = parse_args(&call)?;
         let response = backend
@@ -70,6 +69,6 @@ where
             })
             .await
             .map_err(backend_error_to_function_call)?;
-        Ok(JsonToolOutput::new(json!(response)))
+        Ok(Box::new(JsonToolOutput::new(json!(response))))
     }
 }

codex-rs/ext/memories/src/tools/mod.rs

@@ -1,9 +1,9 @@
 use std::sync::Arc;
 
-use codex_extension_api::ExtensionToolExecutor;
 use codex_extension_api::FunctionCallError;
 use codex_extension_api::ResponsesApiTool;
 use codex_extension_api::ToolCall;
+use codex_extension_api::ToolExecutor;
 use codex_extension_api::ToolName;
 use codex_extension_api::ToolSpec;
 use codex_extension_api::parse_tool_input_schema;
@@ -23,7 +23,7 @@ mod list;
 mod read;
 mod search;
 
-pub(crate) fn memory_tools<B>(backend: B) -> Vec<Arc<dyn ExtensionToolExecutor>>
+pub(crate) fn memory_tools<B>(backend: B) -> Vec<Arc<dyn ToolExecutor<ToolCall>>>
 where
     B: MemoriesBackend,
 {

codex-rs/ext/memories/src/tools/read.rs

@@ -38,8 +38,6 @@ impl<B> ToolExecutor<ToolCall> for ReadTool<B>
 where
     B: MemoriesBackend,
 {
-    type Output = JsonToolOutput;
-
     fn tool_name(&self) -> ToolName {
         memory_tool_name(READ_TOOL_NAME)
     }
@@ -54,7 +52,8 @@ where
     async fn handle(
         &self,
         call: ToolCall,
-    ) -> Result<Self::Output, codex_extension_api::FunctionCallError> {
+    ) -> Result<Box<dyn codex_extension_api::ToolOutput>, codex_extension_api::FunctionCallError>
+    {
         let backend = self.backend.clone();
         let args: ReadArgs = parse_args(&call)?;
         let response = backend
@@ -66,6 +65,6 @@ where
             })
             .await
             .map_err(backend_error_to_function_call)?;
-        Ok(JsonToolOutput::new(json!(response)))
+        Ok(Box::new(JsonToolOutput::new(json!(response))))
     }
 }

codex-rs/ext/memories/src/tools/search.rs

@@ -47,8 +47,6 @@ impl<B> ToolExecutor<ToolCall> for SearchTool<B>
 where
     B: MemoriesBackend,
 {
-    type Output = JsonToolOutput;
-
     fn tool_name(&self) -> ToolName {
         memory_tool_name(SEARCH_TOOL_NAME)
     }
@@ -63,14 +61,15 @@ where
     async fn handle(
         &self,
         call: ToolCall,
-    ) -> Result<Self::Output, codex_extension_api::FunctionCallError> {
+    ) -> Result<Box<dyn codex_extension_api::ToolOutput>, codex_extension_api::FunctionCallError>
+    {
         let backend = self.backend.clone();
         let args: SearchArgs = parse_args(&call)?;
         let response = backend
             .search(args.into_request())
             .await
             .map_err(backend_error_to_function_call)?;
-        Ok(JsonToolOutput::new(json!(response)))
+        Ok(Box::new(JsonToolOutput::new(json!(response))))
     }
 }