[feat] persist dynamic tools in session rollout file (#10130)

Add dynamic tools to rollout file for persistence & read from rollout on
resume. Ran a real example and spotted the following in the rollout
file:
```
{"timestamp":"2026-01-29T01:27:57.468Z","type":"session_meta","payload":{"id":"019c075d-3f0b-77e3-894e-c1c159b04b1e","timestamp":"2026-01-29T01:27:57.451Z","...."dynamic_tools":[{"name":"demo_tool","description":"Demo dynamic tool","inputSchema":{"additionalProperties":false,"properties":{"city":{"type":"string"}},"required":["city"],"type":"object"}}],"git":{"commit_hash":"ebc573f15c01b8af158e060cfedd401f043e9dfa","branch":"dev/cc/dynamic-tools","repository_url":"https://github.com/openai/codex.git"}}}
```

codex-rs/core/src/codex.rs

@@ -324,6 +324,12 @@ impl Codex {
             .clone()
             .or_else(|| conversation_history.get_base_instructions().map(|s| s.text))
             .unwrap_or_else(|| model_info.get_model_instructions(config.model_personality));
+        // Respect explicit thread-start tools; fall back to persisted tools when resuming a thread.
+        let dynamic_tools = if dynamic_tools.is_empty() {
+            conversation_history.get_dynamic_tools().unwrap_or_default()
+        } else {
+            dynamic_tools
+        };
 
         // TODO (aibrahim): Consolidate config.model and config.model_reasoning_effort into config.collaboration_mode
         // to avoid extracting these fields separately and constructing CollaborationMode here.
@@ -715,6 +721,7 @@ impl Session {
                         BaseInstructions {
                             text: session_configuration.base_instructions.clone(),
                         },
+                        session_configuration.dynamic_tools.clone(),
                     ),
                 )
             }