refactor(editor): rebuild diff viewer around code editor kernels

desktop/dev/viewer.css

@@ -24,7 +24,6 @@
 @import url("../../editor/viewer/contrib/references/browser/references.css");
 @import url("../../editor/viewer/contrib/hover/hover.css");
 @import url("../../editor/viewer/contrib/quick_diff/browser/quick_diff.css");
-@import url("../../editor/viewer/browser/unified_diff/unified_diff.css");
 @import url("../../editor/viewer/contrib/agent_feedback/browser/agent_feedback.css");
 @import url("../../editor/viewer/browser/diagram_viewport/diagram_viewport.css");
 @import url("../../editor/viewer/contrib/markdown_comments/browser/markdown_comments.css");

desktop/frontend/dom_helpers.mbt

@@ -45,11 +45,14 @@ fn host_prefers_dark() -> Bool {
 /// owns the palette; the command keeps the DOM write out of the pure handler.
 fn Theme::apply(self : Theme, system_dark : Bool) -> @cmd.Cmd {
   let value = if self.is_dark(system_dark) { "dark" } else { "light" }
-  @cmd.custom_cmd(_ => {
-    if @dom.document().get_document_element() is Some(root) {
-      root.set_attribute("data-theme", value)
-    }
-  })
+  @cmd.batch([
+    @cmd.custom_cmd(_ => {
+      if @dom.document().get_document_element() is Some(root) {
+        root.set_attribute("data-theme", value)
+      }
+    }),
+    @fileeditor.apply_theme(value),
+  ])
 }
 
 ///|

desktop/frontend/fileeditor/active_editor_surface_wbtest.mbt

@@ -0,0 +1,24 @@
+///|
+test "only the visible editor surface participates in host layout" {
+  assert_true(
+    active_editor_surface_from_visibility(true, false, false)
+    is Some(CodeEditorSurface),
+  )
+  assert_true(
+    active_editor_surface_from_visibility(false, true, false)
+    is Some(MarkdownEditorSurface),
+  )
+  assert_true(
+    active_editor_surface_from_visibility(false, false, true)
+    is Some(DiffEditorSurface),
+  )
+  assert_true(
+    active_editor_surface_from_visibility(false, false, false) is None,
+  )
+  // If a host patch briefly overlaps visibility, the product's most specific
+  // comparison surface wins and parked source surfaces remain untouched.
+  assert_true(
+    active_editor_surface_from_visibility(true, true, true)
+    is Some(DiffEditorSurface),
+  )
+}

desktop/frontend/fileeditor/unified_diff_comment_bridge_wbtest.mbt → desktop/frontend/fileeditor/diff_comment_bridge_wbtest.mbt

@@ -1,18 +1,16 @@
 ///|
 test "full-diff comments cross the Desktop boundary without losing line identity" {
   let file = @pathx.Relative("src/main.mbt")
-  let deletion = unified_diff_comment_message(file, {
-    line: {
-      kind: @unified_diff.Deletion,
-      original_line_number: Some(4),
-      modified_line_number: None,
-      text: "obsolete()",
-    },
-    comment: "good removal",
-  })
+  let deletion = diff_comment_message(
+    file,
+    original_line_number=Some(4),
+    modified_line_number=None,
+    quote="obsolete()",
+    comment="good removal",
+  )
   assert_true(
     deletion
-    is UnifiedDiffCommentAdded(
+    is DiffCommentAdded(
       file=@pathx.Relative("src/main.mbt"),
       original_line_number=Some(4),
       modified_line_number=None,
@@ -22,42 +20,35 @@ test "full-diff comments cross the Desktop boundary without losing line identity
       feedback_id=None
     ),
   )
-  let context = unified_diff_comment_message(file, {
-    line: {
-      kind: @unified_diff.Context,
-      original_line_number: Some(8),
-      modified_line_number: Some(9),
-      text: "shared()",
-    },
-    comment: "keep this",
-  })
+  let context = diff_comment_message(
+    file,
+    original_line_number=Some(8),
+    modified_line_number=Some(9),
+    quote="shared()",
+    comment="keep this",
+  )
   assert_true(
     context
-    is UnifiedDiffCommentAdded(
+    is DiffCommentAdded(
       original_line_number=Some(8),
       modified_line_number=Some(9),
       quote="shared()",
       comment="keep this",
       ..
     ),
   )
-  let original_viewer = unified_diff_comment_message(
+  let original_editor = diff_comment_message(
     file,
-    {
-      line: {
-        kind: @unified_diff.Deletion,
-        original_line_number: Some(12),
-        modified_line_number: None,
-        text: "removed()",
-      },
-      comment: "restore this",
-    },
+    original_line_number=Some(12),
+    modified_line_number=None,
+    quote="removed()",
+    comment="restore this",
     resource=ModelUri("openseek-review-original://workspace/src/main.mbt"),
     feedback_id="feedback-12",
   )
   assert_true(
-    original_viewer
-    is UnifiedDiffCommentAdded(
+    original_editor
+    is DiffCommentAdded(
       original_line_number=Some(12),
       modified_line_number=None,
       resource=Some(

desktop/frontend/fileeditor/diff_provider_policy_wbtest.mbt

@@ -0,0 +1,90 @@
+///|
+test "diff provider forces Core outside .mbt without overwriting preference" {
+  assert_true(
+    effective_diff_provider_mode(ReviewDiffTree, true)
+    is @moon_diff_provider.Tree,
+  )
+  assert_true(
+    effective_diff_provider_mode(ReviewDiffTree, false)
+    is @moon_diff_provider.Core,
+  )
+  assert_true(supports_moon_diff("SRC/MAIN.MBT"))
+  assert_false(supports_moon_diff("src/main.mbti"))
+}
+
+///|
+test "desktop diff provider preferences and fallback status are host state" {
+  let initial = State::empty()
+  assert_true(initial.review_diff_mode is ReviewDiffCore)
+  assert_true(initial.review_diff_ignore_comments)
+  assert_eq(initial.review_diff_status, None)
+
+  let path = @pathx.Relative("src/main.mbt")
+  let selected = test_modified_change(path)
+  let docs = owned_state().docs.copy()
+  docs[path] = {
+    ..loaded_doc(path.0),
+    review: Some({
+      generation: 1,
+      working_generation: 1,
+      baseline: ReviewContent("old source"),
+      view_mode: ReviewDiff,
+      selected,
+    }),
+  }
+  let state = { ..owned_state(), docs, }
+  let ctx = { ..test_ctx(), open_files: [path], active_file: Some(path) }
+  let (_, tree) = update(
+    test_emit(),
+    ReviewDiffModeSelected(ReviewDiffTree),
+    state,
+    ctx,
+  )
+  assert_true(tree.review_diff_mode is ReviewDiffTree)
+  assert_eq(tree.review_diff_status, None)
+  let (_, include_comments) = update(
+    test_emit(),
+    ToggleReviewDiffIgnoreComments,
+    tree,
+    ctx,
+  )
+  assert_false(include_comments.review_diff_ignore_comments)
+  let fallback : ReviewDiffStatus = {
+    requested: ReviewDiffTree,
+    effective: ReviewDiffToken,
+    fell_back: true,
+  }
+  let (_, settled) = update(
+    test_emit(),
+    ReviewDiffStatusChanged(fallback),
+    include_comments,
+    ctx,
+  )
+  assert_eq(settled.review_diff_status, Some(fallback))
+}
+
+///|
+test "non-MoonBit review parks the last Moon provider preference" {
+  let path = @pathx.Relative("README.md")
+  let selected = test_modified_change(path)
+  let docs = owned_state().docs.copy()
+  docs[path] = {
+    ..loaded_doc(path.0),
+    review: Some({
+      generation: 1,
+      working_generation: 1,
+      baseline: ReviewContent("old text"),
+      view_mode: ReviewDiff,
+      selected,
+    }),
+  }
+  let state = { ..owned_state(), docs, review_diff_mode: ReviewDiffTree }
+  let ctx = { ..test_ctx(), open_files: [path], active_file: Some(path) }
+  let (_, unchanged) = update(
+    test_emit(),
+    ReviewDiffModeSelected(ReviewDiffToken),
+    state,
+    ctx,
+  )
+  assert_true(unchanged.review_diff_mode is ReviewDiffTree)
+}