feat(panels): taller commit-detail card with initial-commit diff line

The expanded 里程碑详情 card was title+buttons only (60px) and showed no
diff context. Match TS image: grow it to 84px and add the diff status line
between title and buttons. The root commit shows '初始提交 — 没有父提交可对比'
(git.history.diff.initialCommit); later commits leave it blank until the
semantic node-diff summary lands.

- op-git: Commit.is_initial (parent_count == 0)
- op-editor-core: GitCommitSummary.is_initial
- op-host-desktop: plumb is_initial into the snapshot
- op-editor-ui: CARD_H 60→84, button row drops to +52, conditional diff line

crates/op-editor-core/src/editor_ui_state.rs

@@ -130,6 +130,10 @@ pub struct GitCommitSummary {
     /// taken (TS `formatCompactTime`). The widget layer is platform-free
     /// and has no wall clock, so it cannot derive this itself.
     pub time_label: String,
+    /// `true` for the root commit (no parent). The expanded detail card
+    /// shows the "initial commit — nothing to diff" line for it (TS
+    /// `git.history.diff.initialCommit`).
+    pub is_initial: bool,
 }
 
 /// One changed file in the Git panel's staging list — plain data

crates/op-editor-ui/src/widgets/git_panel_ready.rs

@@ -39,10 +39,11 @@ const HISTORY_FIRST: f32 = COMMIT_TOP + COMMIT_H + 24.0;
 const ROW_H: f32 = 26.0;
 const MAX_COMMITS: usize = 8;
 const SUMMARY_MAX: usize = 34;
-/// Height of the inline commit-detail card (里程碑详情 title + a
-/// restore/copy-hash button row) inserted under an expanded commit row
-/// (TS `HistoryMilestoneRow` detail block). Pushes later rows down.
-const CARD_H: f32 = 60.0;
+/// Height of the inline commit-detail card (里程碑详情 title + a diff
+/// status line + a restore/copy-hash button row) inserted under an
+/// expanded commit row (TS `HistoryMilestoneRow` detail block). Pushes
+/// later rows down.
+const CARD_H: f32 = 84.0;
 /// Per-char advance heuristic for the branch label (keeps paint +
 /// hit-test aligned without measuring text).
 const BRANCH_CHAR_W: f32 = 7.5;
@@ -96,7 +97,8 @@ impl GitPanel<'_> {
     /// `(恢复, 复制哈希)` button rects for the inline card whose top edge
     /// is `card_top`. Backend-free fixed widths keep paint + hit aligned.
     fn commit_card_button_rects(&self, rect: Rect, card_top: f32) -> (Rect, Rect) {
-        let btn_y = card_top + 30.0;
+        // Title at +18, diff line at +40, button row at +52 (h24) → 84.
+        let btn_y = card_top + 52.0;
         let h = 24.0;
         let x = rect.origin.x + 40.0; // align with the message column (`pl-10`)
         let restore = Rect {
@@ -416,7 +418,7 @@ impl GitPanel<'_> {
                 // `ready_commit_card_buttons` lands on the same geometry.
                 if self.state.expanded_commit == Some(i) {
                     let card_top = y - 6.0;
-                    self.paint_commit_card(cx, rect, card_top);
+                    self.paint_commit_card(cx, rect, card_top, commit.is_initial);
                     y += CARD_H;
                 }
             }
@@ -424,10 +426,11 @@ impl GitPanel<'_> {
     }
 
     /// Paint the inline commit-detail card (里程碑详情) — a muted band
-    /// with the detail title and a `恢复` / `复制哈希` button row. TS
-    /// `HistoryMilestoneRow` detail block; the inline diff summary is
-    /// deferred (the semantic node-diff is a separate subsystem).
-    fn paint_commit_card(&self, cx: &mut PaintCx<'_>, rect: Rect, card_top: f32) {
+    /// with the detail title, a diff status line, and a `恢复` / `复制哈希`
+    /// button row. TS `HistoryMilestoneRow` detail block. The root commit
+    /// shows the "no parent to diff against" line; the semantic node-diff
+    /// summary for later commits is deferred (a separate subsystem).
+    fn paint_commit_card(&self, cx: &mut PaintCx<'_>, rect: Rect, card_top: f32, is_initial: bool) {
         let t = self.theme;
         cx.backend.fill_rect(
             Rect {
@@ -445,6 +448,19 @@ impl GitPanel<'_> {
             11.0,
             t.foreground,
         );
+        // Diff status line. The root commit has no parent to diff against
+        // (TS `git.history.diff.initialCommit`); non-root commits leave it
+        // blank until the semantic node-diff summary lands.
+        if is_initial {
+            self.text(
+                cx,
+                self.t("git.history.diff.initialCommit"),
+                rect.origin.x + 40.0,
+                card_top + 40.0,
+                11.0,
+                alpha(t.muted_foreground, 0.85),
+            );
+        }
         let (restore, copy) = self.commit_card_button_rects(rect, card_top);
         // 恢复 — outline button.
         cx.backend.stroke_round_rect(restore, 6.0, t.border, 1.0);

crates/op-editor-ui/src/widgets/git_panel_tests.rs

@@ -52,6 +52,7 @@ fn open_panel_height_grows_with_commits() {
                 summary: "first".into(),
                 author: "Ada".into(),
                 time_label: "now".into(),
+                is_initial: false,
             };
             3
         ],
@@ -70,6 +71,7 @@ fn empty_history_reserves_a_placeholder_row() {
             summary: "only".into(),
             author: "Ada".into(),
             time_label: "now".into(),
+            is_initial: false,
         }],
         ..open_repo()
     });
@@ -162,12 +164,14 @@ fn commit_rows_open_a_commit_diff() {
                 summary: "first".into(),
                 author: "Ada".into(),
                 time_label: "now".into(),
+                is_initial: false,
             },
             GitCommitSummary {
                 short_hash: "bbb2222".into(),
                 summary: "second".into(),
                 author: "Bo".into(),
                 time_label: "now".into(),
+                is_initial: false,
             },
         ],
         ..open_repo()
@@ -199,12 +203,14 @@ fn expanded_commit_card_maps_restore_and_copy_and_shifts_later_rows() {
             summary: "first".into(),
             author: "Ada".into(),
             time_label: "now".into(),
+            is_initial: false,
         },
         GitCommitSummary {
             short_hash: "bbb2222".into(),
             summary: "second".into(),
             author: "Bo".into(),
             time_label: "now".into(),
+            is_initial: false,
         },
     ];
     let collapsed = state_with(GitPanelState {
@@ -236,7 +242,7 @@ fn expanded_commit_card_maps_restore_and_copy_and_shifts_later_rows() {
     );
     // Row 1 shifted down by exactly the card height; the panel grew too.
     let row1_expanded = panel.ready_commit_row_rects(rect)[1].origin.y;
-    assert!((row1_expanded - row1_collapsed - 60.0).abs() < 0.5);
+    assert!((row1_expanded - row1_collapsed - 84.0).abs() < 0.5);
     assert!(panel.height() > cp.height());
     // The expanded card sits below row 0's click target.
     let row0 = panel.ready_commit_row_rects(rect)[0];

crates/op-git/src/history.rs

@@ -21,6 +21,9 @@ pub struct Commit {
     pub timestamp: i64,
     /// First line of the commit message.
     pub summary: String,
+    /// `true` for the root commit (no parent) — drives the panel's
+    /// "initial commit, nothing to diff" detail line.
+    pub is_initial: bool,
 }
 
 impl GitRepo {
@@ -139,6 +142,7 @@ fn commit_to_record(commit: &git2::Commit<'_>) -> Commit {
         email: author.email().unwrap_or("").to_string(),
         timestamp: commit.time().seconds(),
         summary: commit.summary().unwrap_or("").to_string(),
+        is_initial: commit.parent_count() == 0,
     }
 }
 
@@ -200,6 +204,7 @@ mod tests {
             email: "ada@x.dev".to_string(),
             timestamp: 1_700_000_000,
             summary: "first commit".to_string(),
+            is_initial: true,
         };
         assert_eq!(c.hash, "abc123");
         assert_eq!(c.short_hash, "abc");

crates/op-host-desktop/src/git_jobs.rs

@@ -140,6 +140,7 @@ fn snapshot(repo: &GitRepo) -> GitSnapshot {
             summary: c.summary,
             author: c.author,
             time_label: format_compact_time(c.timestamp, now_secs),
+            is_initial: c.is_initial,
         })
         .collect();
     let merging = repo.is_merging();