diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index f44f91d6..8f1f6d17 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -12,7 +12,7 @@ needed most.
 
 ## Get it running (about 10 minutes on a fast machine)
 
-You need stable Rust 1.90 or newer. For the web
+You need stable Rust 1.95 or newer (required by egui/eframe 0.36). For the web
 build you also need `rustup target add wasm32-unknown-unknown` and [`trunk`](https://trunkrs.dev).
 
 ```sh
diff --git a/Cargo.toml b/Cargo.toml
index fb1b236a..3cfba562 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -8,7 +8,7 @@ exclude = ["vendor"]
 version = "0.2.1"
 edition = "2024"
 license = "MIT OR Apache-2.0"
-rust-version = "1.90"
+rust-version = "1.95"
 authors = ["SolidCraft contributors"]
 repository = "https://github.com/bherbruck/solidcraft"
 
diff --git a/apps/solvecraft-cli/src/main.rs b/apps/solvecraft-cli/src/main.rs
index 73d2c28f..44d50bca 100644
--- a/apps/solvecraft-cli/src/main.rs
+++ b/apps/solvecraft-cli/src/main.rs
@@ -53,8 +53,17 @@ fn main() -> ExitCode {
         Some("snapshot") => cmd_snapshot(&args[1..]),
         Some("exec") => cmd_exec(&args[1..]),
         Some("commands") => {
+            use std::io::Write as _;
             let mut s = Session::default();
-            s.execute("engine.commands", &json!({})).map(|v| println!("{}", pretty(&v))).map_err(|e| e.to_string())
+            s.execute("engine.commands", &json!({})).map_err(|e| e.to_string()).and_then(|v| {
+                // A pipeline consumer may stop early (e.g. `commands | head`).
+                // Unlike println!, writing explicitly lets us handle that without a panic.
+                match writeln!(std::io::stdout().lock(), "{}", pretty(&v)) {
+                    Ok(()) => Ok(()),
+                    Err(e) if e.kind() == std::io::ErrorKind::BrokenPipe => Ok(()),
+                    Err(e) => Err(format!("stdout: {e}")),
+                }
+            })
         }
         Some("recipe") => args.get(1).ok_or_else(|| USAGE.to_string()).and_then(|p| {
             let v = read_json(p)?;
diff --git a/apps/solvecraft-cli/tests/commands_output.rs b/apps/solvecraft-cli/tests/commands_output.rs
new file mode 100644
index 00000000..7637ba88
--- /dev/null
+++ b/apps/solvecraft-cli/tests/commands_output.rs
@@ -0,0 +1,26 @@
+//! The registry remains valid JSON and a closed pipeline reader must not cause a panic.
+
+use std::process::{Command, Stdio};
+
+#[test]
+fn registry_output_is_complete_json() {
+    let output = Command::new(env!("CARGO_BIN_EXE_solvecraft-cli")).arg("commands").output().unwrap();
+    assert!(output.status.success(), "{}", String::from_utf8_lossy(&output.stderr));
+    let registry: serde_json::Value = serde_json::from_slice(&output.stdout).unwrap();
+    let commands = registry.as_array().unwrap();
+    assert!(commands.iter().any(|command| command["id"] == "solid.box"));
+    assert!(commands.iter().any(|command| command["id"] == "engine.commands"));
+    assert!(output.stdout.ends_with(b"\n"));
+    assert!(output.stderr.is_empty());
+}
+
+#[test]
+fn closed_registry_pipe_exits_without_panicking() {
+    let mut child = Command::new(env!("CARGO_BIN_EXE_solvecraft-cli")).arg("commands").stdout(Stdio::piped()).stderr(Stdio::piped()).spawn().unwrap();
+    // Close our read end before waiting. No sleeps or timing threshold are needed:
+    // the registry is larger than the pipe buffer, so it cannot all be written first.
+    drop(child.stdout.take());
+    let output = child.wait_with_output().unwrap();
+    assert!(output.status.success(), "status: {}; stderr: {}", output.status, String::from_utf8_lossy(&output.stderr));
+    assert!(output.stderr.is_empty(), "{}", String::from_utf8_lossy(&output.stderr));
+}
diff --git a/crates/ui-egui/src/tools.rs b/crates/ui-egui/src/tools.rs
index 5c16b364..14d2aaae 100644
--- a/crates/ui-egui/src/tools.rs
+++ b/crates/ui-egui/src/tools.rs
@@ -327,6 +327,8 @@ fn run_shape(app: &mut SolveApp, t: &Tool) -> Result<Vec<String>, String> {
 pub(crate) fn constraint_preselection(command: &str, selection: &[solvecraft_engine::Sel]) -> Option<Value> {
     use solvecraft_engine::Sel::{SketchCurve, SketchPoint};
     match (command, selection) {
+        ("sketch.constraint.horizontal_vertical", [SketchCurve { id }]) => Some(json!({"line":id})),
+        ("sketch.constraint.horizontal_vertical", [SketchPoint { id: a }, SketchPoint { id: b }]) if a != b => Some(json!({"points":[a,b]})),
         ("sketch.constraint.coincident", [a, b]) => {
             let entity = |s: &solvecraft_engine::Sel| match s {
                 SketchPoint { id } | SketchCurve { id } => Some(id.clone()),
diff --git a/crates/ui-egui/tests/point_alignment.rs b/crates/ui-egui/tests/point_alignment.rs
index 45c6e126..034dcc59 100644
--- a/crates/ui-egui/tests/point_alignment.rs
+++ b/crates/ui-egui/tests/point_alignment.rs
@@ -4,6 +4,97 @@ use serde_json::json;
 use solvecraft_engine::sketch::ConstraintKind;
 use solvecraft_ui_egui::scenario::Harness;
 
+#[test]
+fn horizontal_vertical_uses_preselected_line_and_preserves_rejection() {
+    for fixed in [false, true] {
+        let mut h = Harness::new();
+        h.run(&json!([
+            {"call":"engine.execute","params":{"command":"sketch.create","params":{"plane":"XY"}}},
+            {"call":"engine.execute","params":{"command":"sketch.line","params":{"points":[[10,10],[40,13]],"infer":false}}},
+            {"call":"ui.view","params":{"view":"top"}}
+        ]))
+        .unwrap();
+        if fixed {
+            h.app.session.execute("sketch.constraint.fix", &json!({"entity":"l1"})).unwrap();
+        }
+        h.run(&json!([{"click":{"sketch":[25,11.5]}}])).unwrap();
+        assert_eq!(h.app.session.selection.len(), 1);
+        let selection = h.app.session.selection.clone();
+        let before = serde_json::to_value(&h.app.session.doc).unwrap();
+        let undo = h.app.session.undo.len();
+        h.run(&json!([{"start":"sketch.constraint.horizontal_vertical"}])).unwrap();
+        assert_eq!(h.app.status.as_ref().is_some_and(|(_, _, error)| *error), fixed);
+        if fixed {
+            assert_eq!(serde_json::to_value(&h.app.session.doc).unwrap(), before);
+            assert_eq!(h.app.session.selection, selection);
+            assert_eq!(h.app.session.undo.len(), undo);
+        } else {
+            let sk = &h.app.session.model.state().sketches[0].sketch;
+            let a = sk.point(sk.resolve_point("l1.start").unwrap()).unwrap();
+            let b = sk.point(sk.resolve_point("l1.end").unwrap()).unwrap();
+            assert!((a.y - b.y).abs() < 1e-6);
+            assert_eq!(h.app.session.undo.len(), undo + 1);
+            assert!(h.app.session.selection.is_empty());
+        }
+        assert!(h.app.tool.is_none());
+    }
+}
+
+#[test]
+fn horizontal_vertical_leaves_ambiguous_preselection_to_pick_tool() {
+    use solvecraft_engine::Sel;
+    for selection in [
+        vec![Sel::SketchPoint { id: "origin".into() }],
+        vec![Sel::SketchPoint { id: "origin".into() }, Sel::SketchCurve { id: "c1".into() }],
+        vec![Sel::SketchPoint { id: "origin".into() }, Sel::SketchPoint { id: "c1.center".into() }, Sel::SketchCurve { id: "c1".into() }],
+    ] {
+        let mut h = Harness::new();
+        h.app.session.execute("sketch.create", &json!({"plane":"XY"})).unwrap();
+        h.app.session.execute("sketch.circle.center", &json!({"center":[20,3],"radius":5})).unwrap();
+        h.app.session.selection = selection.clone();
+        let undo = h.app.session.undo.len();
+        h.run(&json!([{"start":"sketch.constraint.horizontal_vertical"}])).unwrap();
+        assert!(h.app.tool.as_ref().unwrap().picks.is_empty());
+        assert_eq!(h.app.session.undo.len(), undo);
+        assert_eq!(h.app.session.selection, selection);
+        assert!(!h.app.status.as_ref().is_some_and(|(_, _, error)| *error));
+    }
+}
+
+#[test]
+fn horizontal_vertical_uses_preselected_points() {
+    for center in [[20.0, 3.0], [3.0, 20.0]] {
+        for reverse in [false, true] {
+            let mut h = Harness::new();
+            let (first, second) = if reverse { (center, [0.0, 0.0]) } else { ([0.0, 0.0], center) };
+            h.run(&json!([
+                {"call":"engine.execute","params":{"command":"sketch.create","params":{"plane":"XY"}}},
+                {"call":"engine.execute","params":{"command":"sketch.circle.center","params":{"center":center,"radius":5}}},
+                {"call":"ui.view","params":{"view":"top"}},
+                {"click":{"sketch":first}},
+                {"click":{"sketch":second},"shift":true}
+            ]))
+            .unwrap();
+            assert_eq!(h.app.session.selection.len(), 2);
+            let before = serde_json::to_value(&h.app.session.doc).unwrap();
+            let undo = h.app.session.undo.len();
+            h.run(&json!([{"start":"sketch.constraint.horizontal_vertical"}])).unwrap();
+            assert!(!h.app.status.as_ref().is_some_and(|(_, _, error)| *error));
+            let sk = &h.app.session.model.state().sketches[0].sketch;
+            let p = sk.point(sk.resolve_point("c1.center").unwrap()).unwrap();
+            assert!((if center[0] > center[1] { p.y } else { p.x }).abs() < 1e-6);
+            assert!(h.app.tool.is_none());
+            assert!(h.app.session.selection.is_empty());
+            assert_eq!(h.app.session.undo.len(), undo + 1);
+            let after = serde_json::to_value(&h.app.session.doc).unwrap();
+            h.app.session.execute("edit.undo", &json!({})).unwrap();
+            assert_eq!(serde_json::to_value(&h.app.session.doc).unwrap(), before);
+            h.app.session.execute("edit.redo", &json!({})).unwrap();
+            assert_eq!(serde_json::to_value(&h.app.session.doc).unwrap(), after);
+        }
+    }
+}
+
 #[test]
 fn horizontal_vertical_aligns_origin_and_circle_center() {
     for (center, horizontal) in [([20.0, 3.0], true), ([3.0, 20.0], false)] {
diff --git a/docs/book/src/guide/getting-started.md b/docs/book/src/guide/getting-started.md
index 7bd63ba0..cf990719 100644
--- a/docs/book/src/guide/getting-started.md
+++ b/docs/book/src/guide/getting-started.md
@@ -8,7 +8,7 @@ were released under the SolveCraft name.
 
 Download the latest build from the
 [releases page](https://github.com/bherbruck/solidcraft/releases), or build it yourself with
-stable Rust (1.90 or newer):
+stable Rust (1.95 or newer):
 
 ```sh
 git clone https://github.com/bherbruck/solidcraft && cd solidcraft
diff --git a/docs/book/src/guide/sketching.md b/docs/book/src/guide/sketching.md
index 29834584..08b0d0a1 100644
--- a/docs/book/src/guide/sketching.md
+++ b/docs/book/src/guide/sketching.md
@@ -96,6 +96,9 @@ distinct straight lines. Two lines join their closest pair of endpoints; the fir
 picked line stays in place when the existing constraints allow it. Pick endpoints
 explicitly when you want to connect a different pair.
 
+Horizontal/Vertical also applies immediately to one selected line or two distinct selected
+points. Shift-click to add the second point before choosing the constraint.
+
 For Parallel, Perpendicular, Equal, Tangent, Concentric and Collinear, select exactly two
 sketch curves (Shift-click to add the second) and choose the constraint to apply it immediately.
 You can also start the constraint first and then pick its curves. An incomplete or mixed