feat: add fetched-at timestamp to markdown header and json meta

tests/e2e_smoke_tests.rs

@@ -13,6 +13,7 @@ fn render_md_reads_json_and_outputs_markdown_to_stdout() {
     "pr_index": 1,
     "title": "t",
     "description": "PR body",
+    "fetched_at": "2026-04-08T12:34:56Z",
     "state": "open",
     "author": "a",
     "base_branch": "main",
@@ -56,6 +57,7 @@ fn render_md_writes_to_out_file_when_requested() {
     "pr_index": 2,
     "title": "t2",
     "description": "PR body",
+    "fetched_at": "2026-04-08T12:34:56Z",
     "state": "open",
     "author": "a",
     "base_branch": "main",
@@ -220,6 +222,7 @@ fn fetch_writes_markdown_to_stdout_by_default() {
 
     let stdout = String::from_utf8(assert.get_output().stdout.clone()).unwrap();
     assert!(stdout.contains("# org/repo `#7` Fix parser"));
+    assert!(stdout.contains("> fetched at: "));
     assert!(stdout.contains("## Commits"));
     assert!(stdout.contains("## Diff Stat"));
     assert!(stdout.contains("## Review 7.1 (COMMENT)"));
@@ -288,5 +291,6 @@ fn fetch_writes_json_to_out_file_when_requested() {
     let written = std::fs::read_to_string(output.path()).unwrap();
     assert!(written.contains("\"repo\": \"org/repo\""));
     assert!(written.contains("\"pr_index\": 8"));
+    assert!(written.contains("\"fetched_at\":"));
     assert!(written.contains("\"head_branch\": \"feature/y\""));
 }

tests/normalize_tests.rs

@@ -141,10 +141,11 @@ fn normalize_groups_replies_and_sorts_threads_by_time() {
         ],
     };
 
-    let doc = normalize_bundle("org/repo", bundle);
+    let doc = normalize_bundle("org/repo", "2026-04-08T12:34:56Z".into(), bundle);
 
     assert_eq!(doc.meta.repo, "org/repo");
     assert_eq!(doc.meta.pr_index, 42);
+    assert_eq!(doc.meta.fetched_at.as_deref(), Some("2026-04-08T12:34:56Z"));
     assert_eq!(doc.meta.base_branch, "main");
     assert_eq!(doc.meta.head_branch, "feature/x");
 
@@ -241,7 +242,7 @@ fn normalize_does_not_merge_unrelated_comments_on_same_file() {
         files: vec![],
     };
 
-    let doc = normalize_bundle("org/repo", bundle);
+    let doc = normalize_bundle("org/repo", "2026-04-08T12:34:56Z".into(), bundle);
 
     assert_eq!(doc.threads.len(), 2);
     assert_eq!(doc.threads[0].root_comment.id, 10);
@@ -297,7 +298,7 @@ fn normalize_uses_non_zero_position_when_line_is_missing() {
         files: vec![],
     };
 
-    let doc = normalize_bundle("org/repo", bundle);
+    let doc = normalize_bundle("org/repo", "2026-04-08T12:34:56Z".into(), bundle);
     assert_eq!(doc.threads.len(), 1);
     assert_eq!(doc.threads[0].root_comment.path.as_deref(), Some("src/main.rs"));
     assert_eq!(doc.threads[0].root_comment.line, Some(41));

tests/render_json_tests.rs

@@ -10,6 +10,7 @@ fn model_json_roundtrip() {
             pr_index: 9,
             title: "feat: x".into(),
             description: Some("desc".into()),
+            fetched_at: Some("2026-04-08T12:34:56Z".into()),
             state: "open".into(),
             author: "alice".into(),
             base_branch: "main".into(),
@@ -50,5 +51,6 @@ fn model_json_roundtrip() {
     let encoded = serde_json::to_string(&doc).unwrap();
     let decoded: PrReviewDocument = serde_json::from_str(&encoded).unwrap();
     assert_eq!(decoded.meta.repo, "org/repo");
+    assert_eq!(decoded.meta.fetched_at.as_deref(), Some("2026-04-08T12:34:56Z"));
     assert_eq!(decoded.threads[0].root_comment.body, "hello");
 }

tests/render_markdown_tests.rs

@@ -12,6 +12,7 @@ fn render_markdown_includes_expected_sections_and_preserves_comment_markdown() {
             pr_index: 7,
             title: "Fix parser".into(),
             description: Some("PR body".into()),
+            fetched_at: Some("2026-04-08T12:34:56Z".into()),
             state: "open".into(),
             author: "alice".into(),
             base_branch: "main".into(),
@@ -72,6 +73,7 @@ fn render_markdown_includes_expected_sections_and_preserves_comment_markdown() {
 
     assert!(md.contains("# org/repo `#7` Fix parser"));
     assert!(md.contains("## Metadata"));
+    assert!(md.contains("> fetched at: 2026-04-08T12:34:56Z"));
     assert!(md.contains("## Commits"));
     assert!(md.contains("## Diff Stat"));
     assert!(md.contains("> 编号规则：Review `<pr>.<review>`；Comment `<pr>.<review>.<comment>`；Reply `<pr>.<review>.<comment>.<reply>`"));
@@ -99,6 +101,7 @@ fn render_markdown_uses_minimal_fence_for_plain_text() {
             pr_index: 1,
             title: "T".into(),
             description: None,
+            fetched_at: None,
             state: "open".into(),
             author: "alice".into(),
             base_branch: "main".into(),