feat(maestro): sidebar cards show diff stats and tool icons

Line 2 of a session card spelled out its blocked work ("1 uncommitted
file") and its command ("claude"). Both now render as marks: the
breakdown as diff notation, and the command's leading program as its
tool's icon in the web client.

The probe carries the line delta of the tracked changes — staged and
unstaged together, against HEAD — so `git add` never makes the counter
drop. Untracked files stay a file count; counting their lines means
reading every one off disk. A tracked change with no line delta falls
back to `~N` rather than claiming `+0 -0`.

The TUI keeps its command as text: a terminal cannot be assumed to have
a font carrying tool glyphs.

crates/maestro-protocol/src/lib.rs

@@ -236,12 +236,71 @@ pub struct InTheWay {
     /// Commits on the branch reachable from no remote-tracking ref.
     #[serde(default)]
     pub unpushed_commits: usize,
+    /// Lines added across the tracked changes — staged and unstaged alike,
+    /// measured against `HEAD`. Untracked files contribute nothing: counting
+    /// their lines means reading every one off disk, and they already have
+    /// their own count above (docs/SIDEBAR.md).
+    #[serde(default)]
+    pub insertions: usize,
+    /// Lines removed across the same tracked changes.
+    #[serde(default)]
+    pub deletions: usize,
 }
 
 impl InTheWay {
     /// Nothing blocks any more — the work has since been committed and pushed.
+    ///
+    /// The line counts are not consulted: they describe the same tracked
+    /// changes `uncommitted_files` counts, and a change with no line delta —
+    /// a mode change, a rename — still blocks.
     pub fn is_clear(&self) -> bool {
-        *self == Self::default()
+        self.uncommitted_files == 0 && self.untracked_files == 0 && self.unpushed_commits == 0
+    }
+}
+
+/// Which fragment of the compact blocked-work stat a value is, and so which
+/// colour the client paints it (docs/SIDEBAR.md).
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum StatKind {
+    /// Lines added.
+    Added,
+    /// Lines removed.
+    Removed,
+    /// Changed tracked files, when the change carries no line delta.
+    Files,
+    /// Untracked files.
+    Untracked,
+    /// Unpushed commits.
+    Unpushed,
+}
+
+impl InTheWay {
+    /// The breakdown as diff notation: `+124`, `-18`, `?3`, `↑2`.
+    ///
+    /// The line counts cover tracked changes only, so a tree whose only
+    /// tracked change carries no line delta — a mode change, a rename —
+    /// reports the file count (`~2`) rather than claiming `+0 -0`. Both
+    /// sidebars render exactly these fragments; [`Display`](std::fmt::Display)
+    /// remains the spelled-out phrasing for the kill refusal and the tooltip.
+    pub fn stats(&self) -> Vec<(StatKind, String)> {
+        let mut out = Vec::new();
+        if self.insertions > 0 || self.deletions > 0 {
+            if self.insertions > 0 {
+                out.push((StatKind::Added, format!("+{}", self.insertions)));
+            }
+            if self.deletions > 0 {
+                out.push((StatKind::Removed, format!("-{}", self.deletions)));
+            }
+        } else if self.uncommitted_files > 0 {
+            out.push((StatKind::Files, format!("~{}", self.uncommitted_files)));
+        }
+        if self.untracked_files > 0 {
+            out.push((StatKind::Untracked, format!("?{}", self.untracked_files)));
+        }
+        if self.unpushed_commits > 0 {
+            out.push((StatKind::Unpushed, format!("↑{}", self.unpushed_commits)));
+        }
+        out
     }
 }
 
@@ -544,6 +603,50 @@ mod tests {
         assert!(is_compatible("unknown"));
     }
 
+    /// docs/SIDEBAR.md: the sidebars render the breakdown as diff notation.
+    #[test]
+    fn stats_read_as_a_diff() {
+        let w = InTheWay {
+            uncommitted_files: 3,
+            untracked_files: 2,
+            unpushed_commits: 1,
+            insertions: 124,
+            deletions: 18,
+        };
+        let text: Vec<String> = w.stats().into_iter().map(|(_, t)| t).collect();
+        assert_eq!(text, ["+124", "-18", "?2", "↑1"]);
+        let kinds: Vec<StatKind> = w.stats().into_iter().map(|(k, _)| k).collect();
+        assert_eq!(
+            kinds,
+            [
+                StatKind::Added,
+                StatKind::Removed,
+                StatKind::Untracked,
+                StatKind::Unpushed
+            ]
+        );
+    }
+
+    /// A change with no line delta — a mode change — still has to say
+    /// something, and `+0 -0` would be a lie about the tree.
+    #[test]
+    fn stats_fall_back_to_the_file_count_without_a_line_delta() {
+        let w = InTheWay {
+            uncommitted_files: 2,
+            ..InTheWay::default()
+        };
+        let text: Vec<String> = w.stats().into_iter().map(|(_, t)| t).collect();
+        assert_eq!(text, ["~2"]);
+        assert!(!w.is_clear());
+    }
+
+    /// A clear tree says nothing at all — the fragment is omitted, not empty.
+    #[test]
+    fn a_clear_tree_has_no_stats() {
+        assert!(InTheWay::default().stats().is_empty());
+        assert!(InTheWay::default().is_clear());
+    }
+
     fn round_trip<T>(value: &T) -> T
     where
         T: Serialize + for<'de> Deserialize<'de>,