feat(core): emit canonical review mode items (#31473)

## Description

This PR moves review-mode markers onto canonical `TurnItem` lifecycle:

- `TurnItem::EnteredReviewMode`
- `TurnItem::ExitedReviewMode`

Core now emits `ItemStarted` / `ItemCompleted` for both. The completed
items map back into the existing `EnteredReviewMode` /
`ExitedReviewMode` events, so raw core event consumers and legacy
rollout persistence keep seeing the old events.

This is the compatibility layer needed before paginated rollouts persist
review markers as `ItemCompleted(TurnItem)`.

## Why

Review markers were one of the remaining app-server thread items created
directly from legacy events. Giving them canonical items lets paginated
history persist stable turn/item IDs without changing legacy rollouts.

## What changed

- Added canonical review-mode `TurnItem`s and switched review flow to
emit their lifecycle.
- Added completed-item → legacy review event mappings with stable
turn/item IDs.
- Switched app-server live notifications to the generic canonical item
path and kept legacy replay compatible with old payloads.
- Updated `ThreadHistoryBuilder` to replay canonical review items even
though review turns still do not emit `TurnStarted`.

codex-rs/protocol/src/review_format.rs

@@ -0,0 +1,82 @@
+use crate::protocol::ReviewFinding;
+use crate::protocol::ReviewOutputEvent;
+
+// These helpers return plain strings that higher layers 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}")
+}
+
+/// Fallback text used when a review contains no displayable output.
+pub const REVIEW_FALLBACK_MESSAGE: &str = "Reviewer failed to output a response.";
+
+/// 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();
+    lines.push(String::new());
+
+    // Header
+    if findings.len() > 1 {
+        lines.push("Full review comments:".to_string());
+    } else {
+        lines.push("Review comment:".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")
+}
+
+/// Render a human-readable review summary suitable for a user-facing message.
+///
+/// Returns either the explanation, the formatted findings block, or both
+/// separated by a blank line. If neither is present, emits a fallback message.
+pub fn render_review_output_text(output: &ReviewOutputEvent) -> String {
+    let mut sections = Vec::new();
+    let explanation = output.overall_explanation.trim();
+    if !explanation.is_empty() {
+        sections.push(explanation.to_string());
+    }
+    if !output.findings.is_empty() {
+        let findings = format_review_findings_block(&output.findings, /*selection*/ None);
+        let trimmed = findings.trim();
+        if !trimmed.is_empty() {
+            sections.push(trimmed.to_string());
+        }
+    }
+    if sections.is_empty() {
+        REVIEW_FALLBACK_MESSAGE.to_string()
+    } else {
+        sections.join("\n\n")
+    }
+}