Keep incremental rendering with visualization context (#34217)

## Why

Providing an inline visualization context forced every streamed Markdown update
to rerender the full response, even when the source contained no visualization
directives.

## What changed

- Preserve the stable rendered prefix when visualization context is available
  but no directive is present.
- Continue using canonical full rendering when the source contains a
  visualization directive.

## Testing

Added a regression test that verifies directive-free streams match full
rendering while advancing the stable source boundary.

GitOrigin-RevId: cd70d2ba052db822d474eba8619d04cedf4c0573

codex-rs/tui/src/streaming/render.rs

@@ -102,7 +102,7 @@ impl StreamingRender {
             return;
         }
 
-        if inline_visualization_context.is_some() || raw_source.contains(DIRECTIVE_PREFIX) {
+        if raw_source.contains(DIRECTIVE_PREFIX) {
             self.recompute(
                 raw_source,
                 width,

codex-rs/tui/src/streaming/render_tests.rs

@@ -165,6 +165,40 @@ fn incremental_raw_render_preserves_blank_lines() {
     );
 }
 
+#[test]
+fn inline_visualization_context_without_directives_keeps_stable_prefix() {
+    let cwd = test_cwd();
+    let context = InlineVisualizationContext::new(&cwd, ThreadId::new())
+        .expect("UUIDv7 thread id should provide a timestamp");
+    let width = Some(80);
+    let mut source = String::new();
+    let mut render = StreamingRender::new();
+
+    for chunk in ["First paragraph.\n\n", "Second paragraph.\n\n"] {
+        source.push_str(chunk);
+        render.append(
+            &source,
+            chunk,
+            width,
+            &cwd,
+            HistoryRenderMode::Rich,
+            Some(&context),
+        );
+        assert_eq!(
+            render.lines,
+            render_source(
+                &source,
+                width,
+                &cwd,
+                HistoryRenderMode::Rich,
+                Some(&context),
+            ),
+        );
+    }
+
+    assert!(render.stable_source_len > 0);
+}
+
 #[test]
 fn inline_visualizations_use_canonical_full_render() {
     let cwd = test_cwd();