Preserve parent tool declarations in prediction forks (#57287)

## What changed

Keep inherited incremental tool declarations in MCP-disabled prediction forks and `thread/sample` requests, and append a developer notice that MCP tools are unavailable. Skip tool declaration updates within the inherited context window; new windows still declare the current tools.

Add the default-enabled `prediction_preserve_parent_tools` feature flag and its configuration schema entries.

## Testing

Update core snapshots and app-server tests to cover inherited declarations, the MCP-unavailable notice, preservation across MCP refresh, and continued parent tool availability.

GitOrigin-RevId: 3adf96c7d0e0093986dbdbd540bd47674a2c105c

codex-rs/features/src/lib.rs

@@ -287,6 +287,8 @@ pub enum Feature {
     DeferredToolWorldState,
     /// Track top-level tool definitions in world state and emit incremental context updates.
     IncrementalTools,
+    /// Preserve inherited tool declarations in MCP-disabled prediction forks.
+    PredictionPreserveParentTools,
     /// Expose MCP model-visible namespaces without the legacy `mcp__` prefix.
     NonPrefixedMcpToolNames,
     /// Enable discoverable tool suggestions for apps.
@@ -1695,6 +1697,12 @@ pub const FEATURES: &[FeatureSpec] = &[
         stage: Stage::Stable,
         default_enabled: true,
     },
+    FeatureSpec {
+        id: Feature::PredictionPreserveParentTools,
+        key: "prediction_preserve_parent_tools",
+        stage: Stage::Stable,
+        default_enabled: true,
+    },
     FeatureSpec {
         id: Feature::NonPrefixedMcpToolNames,
         key: "non_prefixed_mcp_tool_names",