fix: Include milestones in critical path calculation

Milestones (tasks with zero duration) were incorrectly excluded from
the critical path due to a `duration_days > 0` check.

Before: `is_critical: node.slack == 0 && node.duration_days > 0`
After:  `is_critical: node.slack == 0`

This affected both:
- The `is_critical` flag on ScheduledTask
- The `critical_path` vector in Schedule

Milestones with zero slack are now correctly marked as critical and
included in the critical path output.

Fixes the CTL PIII bug where "[7.6] TTG Release" milestone had 0 slack
but wasn't shown as critical.

Tests: Added `milestone_can_be_critical` regression test

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: alanbld

Cargo.toml

@@ -14,7 +14,7 @@ members = [
 ]
 
 [workspace.package]
-version = "0.9.2"
+version = "0.9.3"
 edition = "2021"
 rust-version = "1.75"
 license = "MIT OR Apache-2.0"
@@ -24,10 +24,10 @@ categories = ["command-line-utilities", "development-tools"]
 
 [workspace.dependencies]
 # Internal crates (version required for crates.io publishing)
-utf8proj-core = { version = "0.9.2", path = "crates/utf8proj-core" }
-utf8proj-parser = { version = "0.9.2", path = "crates/utf8proj-parser" }
-utf8proj-solver = { version = "0.9.2", path = "crates/utf8proj-solver" }
-utf8proj-render = { version = "0.9.2", path = "crates/utf8proj-render" }
+utf8proj-core = { version = "0.9.3", path = "crates/utf8proj-core" }
+utf8proj-parser = { version = "0.9.3", path = "crates/utf8proj-parser" }
+utf8proj-solver = { version = "0.9.3", path = "crates/utf8proj-solver" }
+utf8proj-render = { version = "0.9.3", path = "crates/utf8proj-render" }
 
 # Date/Time
 chrono = { version = "0.4", features = ["serde"] }

crates/utf8proj-solver/src/lib.rs

@@ -3105,9 +3105,10 @@ impl Scheduler for CpmSolver {
             .map(|(i, id)| (id, i))
             .collect();
 
+        // Critical path includes all tasks with zero slack (including milestones)
         let mut critical_path: Vec<TaskId> = nodes
             .iter()
-            .filter(|(_, node)| node.slack == 0 && node.duration_days > 0)
+            .filter(|(_, node)| node.slack == 0)
             .map(|(id, _)| id.clone())
             .collect();
 
@@ -3233,7 +3234,7 @@ impl Scheduler for CpmSolver {
                     duration: Duration::days(node.original_duration_days),
                     assignments,
                     slack: Duration::days(node.slack),
-                    is_critical: node.slack == 0 && node.duration_days > 0,
+                    is_critical: node.slack == 0, // Milestones can be critical too
                     early_start: working_day_cache.get(node.early_start),
                     early_finish: if node.duration_days > 0 {
                         working_day_cache.get(node.early_finish - 1)
@@ -3841,6 +3842,34 @@ mod tests {
         assert_eq!(schedule.tasks["done"].start, schedule.tasks["done"].finish);
     }
 
+    #[test]
+    fn milestone_can_be_critical() {
+        // Regression test: milestones with zero slack should be marked critical
+        // Previously, milestones were excluded from critical path due to duration_days > 0 check
+        let mut project = Project::new("Milestone Critical Test");
+        project.start = NaiveDate::from_ymd_opt(2025, 1, 6).unwrap();
+        project.tasks = vec![
+            Task::new("work").effort(Duration::days(5)),
+            Task::new("release").milestone().depends_on("work"),
+        ];
+
+        let solver = CpmSolver::new();
+        let schedule = solver.schedule(&project).unwrap();
+
+        // Both tasks should be critical (linear chain)
+        assert!(schedule.tasks["work"].is_critical, "work should be critical");
+        assert!(
+            schedule.tasks["release"].is_critical,
+            "milestone should be critical when it has zero slack"
+        );
+
+        // Critical path should include milestone
+        assert!(
+            schedule.critical_path.contains(&"release".to_string()),
+            "critical_path should include the milestone"
+        );
+    }
+
     #[test]
     fn nested_tasks_are_flattened() {
         let mut project = Project::new("Nested");