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/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))))
     }
 }