Add dev message upon review out (#3758)

Proposal: We want to record a dev message like so:

```
{
      "type": "message",
      "role": "user",
      "content": [
        {
          "type": "input_text",
          "text": "<user_action>
  <context>User initiated a review task. Here's the full review output from reviewer model. User may select one or more comments to resolve.</context>
  <action>review</action>
  <results>
  {findings_str}
  </results>
</user_action>"
        }
      ]
    },
```

Without showing in the chat transcript.

Rough idea, but it fixes issue where the user finishes a review thread,
and asks the parent "fix the rest of the review issues" thinking that
the parent knows about it.

### Question: Why not a tool call?

Because the agent didn't make the call, it was a human. + we haven't
implemented sub-agents yet, and we'll need to think about the way we
represent these human-led tool calls for the agent.

codex-rs/core/src/review_format.rs

@@ -0,0 +1,55 @@
+use crate::protocol::ReviewFinding;
+
+// Note: We keep this module UI-agnostic. It returns plain strings that
+// higher layers (e.g., TUI) may style as needed.
+
+fn format_location(item: &ReviewFinding) -> String {
+    let path = item.code_location.absolute_file_path.display();
+    let start = item.code_location.line_range.start;
+    let end = item.code_location.line_range.end;
+    format!("{path}:{start}-{end}")
+}
+
+/// Format a full review findings block as plain text lines.
+///
+/// - When `selection` is `Some`, each item line includes a checkbox marker:
+///   "[x]" for selected items and "[ ]" for unselected. Missing indices
+///   default to selected.
+/// - When `selection` is `None`, the marker is omitted and a simple bullet is
+///   rendered ("- Title — path:start-end").
+pub fn format_review_findings_block(
+    findings: &[ReviewFinding],
+    selection: Option<&[bool]>,
+) -> String {
+    let mut lines: Vec<String> = Vec::new();
+
+    // Header
+    let header = if findings.len() > 1 {
+        "Full review comments:"
+    } else {
+        "Review comment:"
+    };
+    lines.push(header.to_string());
+
+    for (idx, item) in findings.iter().enumerate() {
+        lines.push(String::new());
+
+        let title = &item.title;
+        let location = format_location(item);
+
+        if let Some(flags) = selection {
+            // Default to selected if index is out of bounds.
+            let checked = flags.get(idx).copied().unwrap_or(true);
+            let marker = if checked { "[x]" } else { "[ ]" };
+            lines.push(format!("- {marker} {title} — {location}"));
+        } else {
+            lines.push(format!("- {title} — {location}"));
+        }
+
+        for body_line in item.body.lines() {
+            lines.push(format!("  {body_line}"));
+        }
+    }
+
+    lines.join("\n")
+}