Add file.import replace mode for empty-project round-trips.

Headless import merged into the current project, so a demo or leftover timeline mixed into export. replace:true starts from file.newProject with the same name, then imports, which is the documented empty-project-start workflow.

crates/engine/src/commands.rs

@@ -913,7 +913,7 @@ fn build() -> Vec<CommandSpec> {
                 Ok(json!({"items": ids.iter().map(|i| i.0).collect::<Vec<_>>()}))
             }
         ),
-        cmd!("file.import", "Import…", ["File"], Some("Cmd+I"), r#"{"paths":[str],"bin":binId?,"imageSequence":bool?}"#, always, |s, p| {
+        cmd!("file.import", "Import…", ["File"], Some("Cmd+I"), r#"{"paths":[str],"bin":binId?,"imageSequence":bool?,"replace":bool?}"#, always, |s, p| {
             let bin = u64_p(p, "bin").map(filmcraft_project::BinId);
             let paths: Vec<String> = match p.get("paths").and_then(Value::as_array) {
                 Some(a) => a.iter().filter_map(|v| v.as_str().map(str::to_string)).collect(),
@@ -922,6 +922,10 @@ fn build() -> Vec<CommandSpec> {
             if paths.is_empty() {
                 return Err(bad("file.import", "need `paths`"));
             }
+            if bool_p(p, "replace").unwrap_or(false) {
+                let name = s.project.name.clone();
+                s.execute("file.newProject", json!({ "name": name }))?;
+            }
             let mut ids = Vec::new();
             let mut errors = Vec::new();
             let mut sequences = Vec::new();

crates/engine/src/image_sequence_tests.rs

@@ -11,6 +11,24 @@ use serde_json::{Value, json};
 use crate::Session;
 use crate::media_test_util::tmp_dir;
 
+#[test]
+fn import_replace_starts_from_an_empty_project() {
+    let dir = tmp_dir("import-replace");
+    let wav = dir.join("tone.wav");
+    std::fs::write(&wav, filmcraft_media::wav::write_wav16(&[0.1; 4800], 2, 48_000)).unwrap();
+    let mut s = demo();
+    let demo_items = s.project.items.len();
+    assert!(demo_items > 1);
+    assert!(!s.state.open_sequences.is_empty());
+    s.execute("file.import", json!({"paths": [wav.to_string_lossy()], "replace": true})).unwrap();
+    assert!(s.state.open_sequences.is_empty());
+    assert_eq!(s.project.items.len(), 1);
+    assert!(s.project.items.values().any(|it| it.name == "tone.wav"));
+    let mut merge = demo();
+    merge.execute("file.import", json!({"paths": [wav.to_string_lossy()]})).unwrap();
+    assert!(merge.project.items.len() > demo_items);
+}
+
 fn demo() -> Session {
     let mut s = Session::default();
     s.execute("file.openDemoProject", json!({})).unwrap();

docs/architecture.md

@@ -694,7 +694,9 @@ Video encoders implement `export::VideoEncoder`. Codec crates plug in with `regi
 
 Timelines can be exchanged as EDL, FCP7 XML, FCPXML, OTIO, AAF or OMF. `file.import` detects these
 formats and merges the result into the project as one undoable step (AAF / OMF embedded audio is
-written next to the document first), and `file.exportInterchange`, `file.exportEdl`,
+written next to the document first). `file.import {replace: true}` starts from an empty project
+with the same name (`file.newProject`) so a headless import→export round-trip contains only the
+imported timeline. `file.exportInterchange`, `file.exportEdl`,
 `file.exportFcpxml`, `file.exportOtio`, `file.exportAaf` and `file.exportOmf` write them.
 `file.exportInterchange {format}` takes `edl`, `xml` (the default), `fcpxml`, `otio`, `aaf` or `omf`;
 any other value is a parameter error and nothing is written. For AAF and