Finalize model-specific tool plans in ToolRouter (#41195)

## Why

Planning tools for a candidate model must not change the selected model or its
Responses Lite tool inventory. Otherwise, preparing a fallback can overwrite
metadata before the current model's request is sent.

## What changed

- Build tool registries and visible specs from an explicit `ModelInfo`.
- Store the finalized tool mode, code-mode names, namespace inventory, and
  terminal and child-management capabilities on `ToolRouter`.
- Publish namespace inventory only after selecting the step's router, and use
  that router's mode when dispatching and recording tool calls.

## Testing

Added coverage for candidate-model isolation, fallback compaction metadata,
code-mode worker selection, normalized tool names, and router capabilities.

GitOrigin-RevId: 56df2de8f42c7e93a4c4dcd117720e40a0cca3db

codex-rs/core/src/session/turn_context.rs

@@ -1046,14 +1046,14 @@ impl Session {
 
         if !tc.code_mode_available
             && matches!(
-                crate::tools::requested_tool_mode(tc),
+                crate::tools::requested_tool_mode(tc, tc.model_info()),
                 codex_protocol::openai_models::ToolMode::CodeMode
                     | codex_protocol::openai_models::ToolMode::CodeModeOnly
             )
             && let Some(message) = self
                 .services
                 .code_mode_service
-                .take_unavailable_warning(crate::tools::effective_tool_mode(tc))
+                .take_unavailable_warning(crate::tools::effective_tool_mode(tc, tc.model_info()))
         {
             self.send_event(tc, EventMsg::Warning(WarningEvent { message }))
                 .await;