From 696b64c30fca4c946eb485fa7180df234d8c4ab4 Mon Sep 17 00:00:00 2001
From: jyviko <2501648+jyviko@users.noreply.github.com>
Date: Wed, 14 Oct 2026 21:50:53 -0400
Subject: [PATCH] Session::opened identifies the open document

It changes when file.open, file.recover or file.sample replaces the session
and when geometry.open opens another design file or starts a new model; an
edit, a solve or reopening the same design keep it. The desktop app frames
the view on that change (#233).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo
---
 crates/engine/src/cmd/file.rs     |  1 +
 crates/engine/src/cmd/geometry.rs |  5 ++++
 crates/engine/src/lib.rs          | 42 +++++++++++++++++++++++++++++++
 3 files changed, 48 insertions(+)

diff --git a/crates/engine/src/cmd/file.rs b/crates/engine/src/cmd/file.rs
index 456bbc1..eeda4be 100644
--- a/crates/engine/src/cmd/file.rs
+++ b/crates/engine/src/cmd/file.rs
@@ -232,6 +232,7 @@ impl Session {
         opened.limits = self.limits;
         opened.file_access = std::mem::take(&mut self.file_access);
         opened.clear_history();
+        opened.mark_opened();
         *self = opened;
     }
 }
diff --git a/crates/engine/src/cmd/geometry.rs b/crates/engine/src/cmd/geometry.rs
index fcab884..3c2b30a 100644
--- a/crates/engine/src/cmd/geometry.rs
+++ b/crates/engine/src/cmd/geometry.rs
@@ -90,6 +90,11 @@ fn open(s: &mut Session, p: &Value) -> Result<Value> {
         "related": fit.related,
         "stale": {"mesh_bodies": fit.mesh_bodies, "sets": fit.sets, "seeds": fit.seeds},
     });
+    // Another design file (or a new model) is another document; the same file opened again after
+    // an edit is the same one.
+    if new_model || s.sources.design.as_ref().is_none_or(|d| d.path() != source.path()) {
+        s.mark_opened();
+    }
     s.design = Some(Arc::new(design));
     s.sources.design = Some(source);
     Ok(out)
diff --git a/crates/engine/src/lib.rs b/crates/engine/src/lib.rs
index 9549e17..ff123ed 100644
--- a/crates/engine/src/lib.rs
+++ b/crates/engine/src/lib.rs
@@ -228,6 +228,9 @@ pub struct Session {
     /// The folders commands may read and write files in (an automation client's roots,
     /// docs/mcp.md); unconfined by default. A file replacing the session keeps them.
     pub file_access: fieldcraft_io::roots::Roots,
+    /// Identifies the open document: it changes when another model, sample or design is opened
+    /// in place of the current one, never with an edit (see [`Session::opened`]).
+    opened: u64,
 }
 
 impl Session {
@@ -280,6 +283,19 @@ impl Session {
         Ok(outputs)
     }
 
+    /// Identifies the open document: it changes when `file.open`, `file.recover` or `file.sample`
+    /// replaces the session and when `geometry.open` opens another design file or starts a new
+    /// model with one; an edit, a solve, undo, redo or opening the same design again after an
+    /// edit keep it. A view frames the model again when it changes.
+    pub fn opened(&self) -> u64 {
+        self.opened
+    }
+
+    /// Make the session another document (see [`Session::opened`]).
+    pub(crate) fn mark_opened(&mut self) {
+        self.opened = next_revision();
+    }
+
     /// Identifies the current state (see [`Session::is_dirty`]).
     pub fn revision(&self) -> u64 {
         self.revision
@@ -699,6 +715,32 @@ mod tests {
         s
     }
 
+    /// `opened` changes with another document (a sample, another design file, a new model) and
+    /// stays with an edit, a solve or the same design opened again: views frame on that change.
+    #[test]
+    fn the_open_document_changes_only_when_another_is_opened() {
+        let mut s = Session::default();
+        let start = s.opened();
+        s.execute("file.sample", &json!({"name": "cantilever"})).unwrap();
+        let cantilever = s.opened();
+        assert_ne!(cantilever, start);
+        s.execute("solve.run", &json!({})).unwrap();
+        s.execute("model.material.create", &json!({"name": "Al", "elastic": {"type": "isotropic", "young": 70000, "poisson": 0.33}})).unwrap();
+        assert_eq!(s.opened(), cantilever, "edits and solves keep the document");
+        s.execute("file.sample", &json!({"name": "cantilever"})).unwrap();
+        assert_ne!(s.opened(), cantilever, "a sample opened again is a fresh start");
+
+        let (_dir, path) = sample_design_file(&Plate::default());
+        let before = s.opened();
+        s.execute("geometry.open", &json!({"path": path})).unwrap();
+        let design = s.opened();
+        assert_ne!(design, before, "another design file");
+        s.execute("geometry.open", &json!({"path": path})).unwrap();
+        assert_eq!(s.opened(), design, "the same design opened again after an edit");
+        s.execute("geometry.open", &json!({"path": path, "model": "new"})).unwrap();
+        assert_ne!(s.opened(), design, "a new model");
+    }
+
     #[test]
     fn reopening_the_same_design_keeps_the_mesh_and_definitions() {
         let (_dir, path) = sample_design_file(&Plate::default());