From fa114d5f6b4cd984256f9e5736a9d25b2733bf0e Mon Sep 17 00:00:00 2001
From: Andrew Stein <steinlink@gmail.com>
Date: Wed, 4 Nov 2026 15:42:11 -0500
Subject: [PATCH 1/3] Loosen layout validation

Signed-off-by: Andrew Stein <steinlink@gmail.com>
---
 .github/workflows/build.yaml                  |  6 +-
 docs/md/how_to/javascript/layout.md           | 18 +++--
 .../src/rust/agent/tools.rs                   | 18 +++++
 .../rust/components/main_panel/reconcile.rs   |  3 -
 .../src/rust/config/viewer_config.rs          |  4 +-
 .../src/rust/js/regular_layout.rs             | 67 ++++---------------
 .../src/rust/tasks/sync_update_panels.rs      | 26 ++++++-
 .../test/js/multi_panel/harness.ts            | 24 +------
 .../restore_workspace_layout.spec.ts          | 67 ++++++++++++-------
 9 files changed, 113 insertions(+), 120 deletions(-)

diff --git a/.github/workflows/build.yaml b/.github/workflows/build.yaml
index 051236bfdd..baa24a8db6 100644
--- a/.github/workflows/build.yaml
+++ b/.github/workflows/build.yaml
@@ -721,7 +721,7 @@ jobs:
 
             - name: Package
               if: ${{ steps.config-step.outputs.FULL_RUN }}
-              run: cargo package --config .cargo/release.toml --no-verify --allow-dirty -p perspective -p perspective-viewer -p perspective-js -p perspective-client -p perspective-server -p perspective-python
+              run: cargo package --config .cargo/release.toml --no-verify --allow-dirty -p perspective -p perspective-viewer -p perspective-js -p perspective-client -p perspective-server -p perspective-migrate -p perspective-python
 
             - uses: actions/upload-artifact@v4
               if: ${{ steps.config-step.outputs.FULL_RUN }}
@@ -1104,15 +1104,17 @@ jobs:
             - name: Set up path overrides for perspective .crate contents
               shell: bash
               run: |
-                  (cd crates && tar xvf perspective-client-*.crate && tar xvf perspective-server-*.crate)
+                  (cd crates && tar xvf perspective-client-*.crate && tar xvf perspective-server-*.crate && tar xvf perspective-migrate-[0-9]*.crate)
                   CLIENT_CRATE_ROOT=$(ls -d "$PWD"/crates/perspective-client-*/ | head -n 1)
                   SERVER_CRATE_ROOT=$(ls -d "$PWD"/crates/perspective-server-*/ | head -n 1)
+                  MIGRATE_CRATE_ROOT=$(ls -d "$PWD"/crates/perspective-migrate-[0-9]*/ | head -n 1)
 
                   mkdir -p $HOME/.cargo
                   cat > $HOME/.cargo/config.toml <<EOF
                   [patch.crates-io]
                   perspective-client = { path = "$CLIENT_CRATE_ROOT" }
                   perspective-server = { path = "$SERVER_CRATE_ROOT" }
+                  perspective-migrate = { path = "$MIGRATE_CRATE_ROOT" }
                   EOF
 
             - name: Install perspective-python sdist
diff --git a/docs/md/how_to/javascript/layout.md b/docs/md/how_to/javascript/layout.md
index 1a1e91b95e..3049cc2af4 100644
--- a/docs/md/how_to/javascript/layout.md
+++ b/docs/md/how_to/javascript/layout.md
@@ -13,8 +13,8 @@ A layout is built from two kinds of node:
 - `split-layout` divides its space among its `children`. The `orientation`
   decides the direction: `"horizontal"` places the children side by side as
   columns, left to right, and `"vertical"` stacks them as rows, top to bottom.
-  `sizes` gives each child's fraction of the split, one number per child, and
-  the sizes must sum to 1 (`[0.5, 0.5]` is an even split, `[0.25, 0.75]` a
+  `sizes` gives each child's share of the split, one number per child, as
+  proportions of their total (`[0.5, 0.5]` is an even split, `[0.25, 0.75]` a
   narrow column next to a wide one).
 - `tab-layout` is a leaf cell holding a stack of panels, listed by panel id in
   `tabs`. Only one panel of a stack is visible at a time; `selected` is the
@@ -27,7 +27,8 @@ across the bottom row. A split nested directly inside a split of the same
 orientation is flattened into its parent, so `saveWorkspace()` may return an
 equivalent but flatter tree than the one you restored.
 
-Every panel must appear in the layout exactly once.
+Each panel may appear in the layout at most once. A panel the layout leaves out
+is removed, with a warning logged to the console.
 
 ```javascript
 const layout = {
@@ -111,7 +112,7 @@ side by side; arrange them afterwards by restoring a `layout`, as below.
 ## Rearranging existing panels
 
 A `restoreWorkspace()` call with a `layout` but no `panels` keeps every panel
-and only moves them. Name the panels by their existing ids, from
+the layout names and only moves them. Name the panels by their existing ids, from
 `getPanelNames()` or a `saveWorkspace()` token. This is how to move or swap a
 panel, resize a row or column, change a row into a column, or stack panels as
 tabs; nothing is re-created or re-queried.
@@ -149,12 +150,9 @@ the viewer is left exactly as it was. A layout is rejected when:
 
 - a panel id in `tabs` is unknown — without `panels` the ids must be existing
   panel ids, and with `panels` they must be `panels` keys;
-- a panel is missing from the layout, or appears more than once — every panel
-  must be placed exactly once;
-- a `split-layout` has no `children`, or its `sizes` do not have one entry per
-  child, or a size is zero or negative, or the sizes do not sum to 1;
-- a `tab-layout` has empty `tabs`, or its `selected` index is past the end of
-  `tabs`.
+- a panel appears more than once;
+- a `split-layout`'s `sizes` do not have one entry per child, or a size is
+  negative or not finite, or every size is zero.
 
 The error message names the offending node by its path, e.g.
 `layout.children[1].tabs`, and lists the valid panel ids.
diff --git a/rust/perspective-viewer/src/rust/agent/tools.rs b/rust/perspective-viewer/src/rust/agent/tools.rs
index 46008c244e..8fece07847 100644
--- a/rust/perspective-viewer/src/rust/agent/tools.rs
+++ b/rust/perspective-viewer/src/rust/agent/tools.rs
@@ -1217,6 +1217,24 @@ impl PerspectiveViewerElement {
             ));
         }
 
+        if let Some(layout) = args.config.get("layout").filter(|x| !x.is_null()) {
+            let layout: crate::js::Layout = serde_json::from_value(layout.clone())?;
+            let ids = self
+                .workspace
+                .panel_ids()
+                .iter()
+                .map(|id| id.as_str().to_owned())
+                .collect::<Vec<_>>();
+
+            let unplaced = layout.validate(&ids).map_err(ToolError)?;
+            if !unplaced.is_empty() {
+                return Err(ToolError(format!(
+                    "Invalid layout: panels {unplaced:?} are missing - name every panel, or \
+                     remove it first with `remove_panel`"
+                )));
+            }
+        }
+
         let snapshot = self.agent_save_workspace().await?;
         if let Some(derived) = args.config.get("derived_tables") {
             self.agent_check_derived(&snapshot, derived).await?;
diff --git a/rust/perspective-viewer/src/rust/components/main_panel/reconcile.rs b/rust/perspective-viewer/src/rust/components/main_panel/reconcile.rs
index 4348dbc82c..9ca1a3090b 100644
--- a/rust/perspective-viewer/src/rust/components/main_panel/reconcile.rs
+++ b/rust/perspective-viewer/src/rust/components/main_panel/reconcile.rs
@@ -41,9 +41,6 @@ const LAYOUT_PHYSICS: LayoutPhysics = LayoutPhysics {
 };
 
 impl MainPanel {
-    /// Size each STAGED panel's hidden `.psp-staging` wrapper to the exact
-    /// plugin box its promote insert will commit (see
-    /// `.plan/DUPLICATE_STAGING_PREDICTION_PLAN.md`).
     pub(super) fn size_staging_wrappers(&self, ctx: &Context<Self>) {
         let Some(root) = self.main_panel_ref.cast::<web_sys::Element>() else {
             return;
diff --git a/rust/perspective-viewer/src/rust/config/viewer_config.rs b/rust/perspective-viewer/src/rust/config/viewer_config.rs
index 0b1176e4fe..93f1b80ef0 100644
--- a/rust/perspective-viewer/src/rust/config/viewer_config.rs
+++ b/rust/perspective-viewer/src/rust/config/viewer_config.rs
@@ -332,13 +332,13 @@ pub struct ViewerConfigInitial {
     pub plugin: Option<String>,
 
     /// Panel title, shown in its tab. Absent renders the default title.
-    #[ts(optional)]
+    #[ts(optional = nullable)]
     pub title: Option<String>,
 
     /// Theme NAME (e.g. `"Pro Dark"`) — not a CSS value. Valid names are
     /// the Perspective themes loaded on the page. Absent uses the
     /// default.
-    #[ts(optional)]
+    #[ts(optional = nullable)]
     pub theme: Option<String>,
 
     /// Plugin-wide settings (as opposed to the per-column
diff --git a/rust/perspective-viewer/src/rust/js/regular_layout.rs b/rust/perspective-viewer/src/rust/js/regular_layout.rs
index 74a636e158..fddb6a8bdb 100644
--- a/rust/perspective-viewer/src/rust/js/regular_layout.rs
+++ b/rust/perspective-viewer/src/rust/js/regular_layout.rs
@@ -317,32 +317,16 @@ impl Layout {
         }
     }
 
-    /// Check that this tree names each of `ids` exactly once and is
-    /// well-formed, describing the first violation found.
-    pub fn validate(&self, ids: &[String]) -> Result<(), String> {
-        if let Layout::Split(split) = self
-            && split.children.is_empty()
-            && split.sizes.is_empty()
-            && ids.is_empty()
-        {
-            return Ok(());
-        }
-
+    /// Check that this tree is well-formed and names each of `ids` at most
+    /// once, returning the `ids` it leaves unplaced.
+    pub fn validate(&self, ids: &[String]) -> Result<Vec<String>, String> {
         let mut seen = Vec::new();
         self.validate_node("layout", ids, &mut seen)?;
-        let missing = ids
+        Ok(ids
             .iter()
             .filter(|id| !seen.contains(id))
-            .collect::<Vec<_>>();
-
-        if !missing.is_empty() {
-            return Err(format!(
-                "Invalid layout: panels {missing:?} are missing - a layout must name every panel \
-                 exactly once (panels: {ids:?})"
-            ));
-        }
-
-        Ok(())
+            .cloned()
+            .collect())
     }
 
     fn validate_node(
@@ -353,32 +337,20 @@ impl Layout {
     ) -> Result<(), String> {
         match self {
             Layout::Split(split) => {
-                if split.children.is_empty() {
-                    return Err(format!("Invalid layout: {path}.children is empty"));
-                }
-
                 if split.sizes.len() != split.children.len() {
                     return Err(format!(
-                        "Invalid layout: {path}.sizes has {} entries for {} children - give one \
-                         size per child",
+                        "Invalid layout: {path}.sizes has {} entries for {} children",
                         split.sizes.len(),
                         split.children.len()
                     ));
                 }
 
-                if let Some(size) = split.sizes.iter().find(|x| !x.is_finite() || **x <= 0.0) {
-                    return Err(format!(
-                        "Invalid layout: {path}.sizes contains {size} - sizes must be positive \
-                         fractions"
-                    ));
+                if let Some(size) = split.sizes.iter().find(|x| !x.is_finite() || **x < 0.0) {
+                    return Err(format!("Invalid layout: {path}.sizes contains {size}"));
                 }
 
-                let total: f64 = split.sizes.iter().sum();
-                if (total - 1.0).abs() > 1e-6 {
-                    return Err(format!(
-                        "Invalid layout: {path}.sizes sum to {total} - sizes are fractions of the \
-                         split and must sum to 1"
-                    ));
+                if !split.sizes.is_empty() && split.sizes.iter().sum::<f64>() <= 0.0 {
+                    return Err(format!("Invalid layout: {path}.sizes sum to zero"));
                 }
 
                 for (index, child) in split.children.iter().enumerate() {
@@ -388,20 +360,6 @@ impl Layout {
                 Ok(())
             },
             Layout::Tab(tab) => {
-                if tab.tabs.is_empty() {
-                    return Err(format!("Invalid layout: {path}.tabs is empty"));
-                }
-
-                if let Some(selected) = tab.selected
-                    && selected >= tab.tabs.len()
-                {
-                    return Err(format!(
-                        "Invalid layout: {path}.selected is {selected} but {path}.tabs has {} \
-                         entries",
-                        tab.tabs.len()
-                    ));
-                }
-
                 for name in &tab.tabs {
                     if !ids.contains(name) {
                         return Err(format!(
@@ -412,8 +370,7 @@ impl Layout {
 
                     if seen.contains(name) {
                         return Err(format!(
-                            "Invalid layout: panel \"{name}\" appears more than once - a layout \
-                             must name every panel exactly once"
+                            "Invalid layout: panel \"{name}\" appears more than once"
                         ));
                     }
 
diff --git a/rust/perspective-viewer/src/rust/tasks/sync_update_panels.rs b/rust/perspective-viewer/src/rust/tasks/sync_update_panels.rs
index 8e20a1fee7..21af6efc71 100644
--- a/rust/perspective-viewer/src/rust/tasks/sync_update_panels.rs
+++ b/rust/perspective-viewer/src/rust/tasks/sync_update_panels.rs
@@ -48,7 +48,7 @@ pub fn sync_update_panels(
         version,
         active,
         layout,
-        panels,
+        mut panels,
         derived_tables,
         global_filters,
         masters,
@@ -68,15 +68,24 @@ pub fn sync_update_panels(
 
     let old_ids = this.workspace.panel_ids();
     let replace = panels.is_some();
+    let mut unplaced = Vec::new();
     if let Some(layout) = &layout {
         let ids = match &panels {
             Some(panels) => panels.keys().cloned().collect::<Vec<_>>(),
             None => old_ids.iter().map(|id| id.as_str().to_owned()).collect(),
         };
 
-        layout
+        unplaced = layout
             .validate(&ids)
             .map_err(|e| ApiError::from(JsValue::from_str(&e)))?;
+
+        for id in &unplaced {
+            tracing::warn!("`layout` does not place panel \"{id}\", dropping it");
+        }
+
+        if let Some(panels) = &mut panels {
+            panels.retain(|id, _| !unplaced.contains(id));
+        }
     }
 
     // Phase 1 — models only, NO renders and NO draws
@@ -124,7 +133,12 @@ pub fn sync_update_panels(
         },
         None => {
             for id in &old_ids {
-                id_map.insert(id.as_str().to_owned(), id.as_str().to_owned());
+                if !unplaced.iter().any(|x| x == id.as_str()) {
+                    id_map.insert(id.as_str().to_owned(), id.as_str().to_owned());
+                } else if let Some(panel) = this.workspace.remove_panel(id) {
+                    panel.renderer.retire_slot();
+                    eject_tasks.push(eject_panel(panel, Disposal::Reject));
+                }
             }
         },
     }
@@ -164,6 +178,12 @@ pub fn sync_update_panels(
         active_target
             .clone()
             .or_else(|| this.workspace.active_id().map(|id| id.as_str().to_owned()))
+            .or_else(|| {
+                this.workspace
+                    .panel_ids()
+                    .first()
+                    .map(|id| id.as_str().to_owned())
+            })
     } else {
         None
     };
diff --git a/rust/perspective-viewer/test/js/multi_panel/harness.ts b/rust/perspective-viewer/test/js/multi_panel/harness.ts
index 9cabb41919..2da5e7f337 100644
--- a/rust/perspective-viewer/test/js/multi_panel/harness.ts
+++ b/rust/perspective-viewer/test/js/multi_panel/harness.ts
@@ -10,24 +10,6 @@
 // ┃ of the [Apache License 2.0](https://www.apache.org/licenses/LICENSE-2.0). ┃
 // ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
 
-// Workspace structural invariants (see `.plan/WORKSPACE_TEST_PLAN.md` §1).
-// Each helper asserts a layer the model-level APIs cannot see, locking the
-// failure classes of the panel-materialization arc:
-//
-// - I1 `armLayoutCanary`/`assertLayoutStable`: the `<regular-layout>` ELEMENT
-//   is never replaced (a Yew unkeyed list diff once recreated it, silently
-//   re-booting an EMPTY layout with no listeners).
-// - I2 `assertTreeSane`: `layout.save()` sizes are finite, positive and
-//   normalized (an insert into an empty split once poisoned the tree with
-//   `NaN` sizes that rendered plausibly).
-// - I3 `assertCoherent`: model panel set ≡ layout tree ≡ frame geometry ≡
-//   slotted plugin projection (a duplicate once committed into an empty tree,
-//   orphaning the original panel from the layout while the model kept both —
-//   and the two frames rendered pixel-superimposed).
-//
-// `armInvariants(test)` retrofits I1+I2+I3 onto a whole spec file; the
-// invariants then gate EVERY test's end state.
-
 import type { Page, TestType } from "@playwright/test";
 import { expect } from "../helpers.ts";
 
@@ -104,7 +86,7 @@ function stackGroups(tree: LayoutTree | null): string[][] {
     return tree.children.flatMap(stackGroups);
 }
 
-/// I2 — every `sizes` entry finite and positive, per-split sum ≈ 1, arity
+/// I2 — every `sizes` entry finite and non-negative, per-split sum > 0, arity
 /// matches, no duplicate or empty slots. The empty root split (zero panels)
 /// is legal.
 export function assertTreeSane(tree: LayoutTree | null): void {
@@ -137,11 +119,11 @@ export function assertTreeSane(tree: LayoutTree | null): void {
         let total = 0;
         for (const size of node.sizes) {
             expect(Number.isFinite(size), `non-finite size ${size}`).toBe(true);
-            expect(size, "non-positive size").toBeGreaterThan(0);
+            expect(size, "negative size").toBeGreaterThanOrEqual(0);
             total += size;
         }
 
-        expect(Math.abs(total - 1), "sizes not normalized").toBeLessThan(1e-6);
+        expect(total, "sizes sum to zero").toBeGreaterThan(0);
         for (const child of node.children) {
             walk(child, false);
         }
diff --git a/rust/perspective-viewer/test/js/multi_panel/restore_workspace_layout.spec.ts b/rust/perspective-viewer/test/js/multi_panel/restore_workspace_layout.spec.ts
index 320c125fcf..6484ca91d7 100644
--- a/rust/perspective-viewer/test/js/multi_panel/restore_workspace_layout.spec.ts
+++ b/rust/perspective-viewer/test/js/multi_panel/restore_workspace_layout.spec.ts
@@ -87,11 +87,6 @@ const INVALID_LAYOUTS: [string, any, string][] = [
         ),
         'unknown panel "nope"',
     ],
-    [
-        "an omitted panel",
-        split("horizontal", [0.5, 0.5], [tab("one"), tab("two")]),
-        "missing",
-    ],
     [
         "a duplicated panel",
         split(
@@ -104,12 +99,7 @@ const INVALID_LAYOUTS: [string, any, string][] = [
     [
         "a sizes length mismatch",
         split("horizontal", [0.5, 0.5], [tab("one"), tab("two"), tab("three")]),
-        "one size per child",
-    ],
-    [
-        "sizes that do not sum to 1",
-        split("horizontal", [1, 1, 1], [tab("one"), tab("two"), tab("three")]),
-        "must sum to 1",
+        "has 2 entries for 3 children",
     ],
     [
         "a negative size",
@@ -118,21 +108,12 @@ const INVALID_LAYOUTS: [string, any, string][] = [
             [1.5, -0.25, -0.25],
             [tab("one"), tab("two"), tab("three")],
         ),
-        "positive",
-    ],
-    [
-        "an empty tab stack",
-        split(
-            "horizontal",
-            [0.5, 0.5],
-            [tab("one", "two", "three"), { type: "tab-layout", tabs: [] }],
-        ),
-        "tabs is empty",
+        "contains -0.25",
     ],
     [
-        "an out-of-range selected tab",
-        { type: "tab-layout", tabs: ["one", "two", "three"], selected: 3 },
-        "selected is 3",
+        "all-zero sizes",
+        split("horizontal", [0, 0, 0], [tab("one"), tab("two"), tab("three")]),
+        "sum to zero",
     ],
 ];
 
@@ -163,6 +144,44 @@ test.describe("restoreWorkspace layout validation", () => {
         expect(result.panels).toEqual(result.names);
     });
 
+    test("drops an existing panel the layout omits", async ({ page }) => {
+        const layout = split("horizontal", [0.5, 0.5], [tab("one"), tab("two")]);
+        const result = await try_restore(page, { layout });
+        expect(result.error).toBeNull();
+        expect(result.panels).toEqual(["one", "two"]);
+        expect(result.after.layout).toEqual(layout);
+        expect(Object.keys(result.after.panels).sort()).toEqual(["one", "two"]);
+    });
+
+    test("drops an incoming panel the layout omits", async ({ page }) => {
+        const layout = split("horizontal", [0.5, 0.5], [tab("a"), tab("b")]);
+        const result = await try_restore(page, {
+            layout,
+            panels: {
+                a: { table: TABLE, plugin: "Debug" },
+                b: { table: TABLE, plugin: "Debug" },
+                c: { table: TABLE, plugin: "Debug" },
+            },
+        });
+
+        expect(result.error).toBeNull();
+        expect(result.panels).toEqual(["a", "b"]);
+        expect(result.after.layout).toEqual(layout);
+    });
+
+    test("accepts sizes that do not sum to 1", async ({ page }) => {
+        const result = await try_restore(page, {
+            layout: split(
+                "horizontal",
+                [1, 2, 1],
+                [tab("one"), tab("two"), tab("three")],
+            ),
+        });
+
+        expect(result.error).toBeNull();
+        expect(result.panels).toEqual(result.names);
+    });
+
     test("rearranges the existing panels into a two-over-one grid", async ({
         page,
     }) => {

From 11e7c32e2c9c304ec95aa5a6c31ca87ec29396ff Mon Sep 17 00:00:00 2001
From: Andrew Stein <steinlink@gmail.com>
Date: Wed, 4 Nov 2026 19:18:36 -0500
Subject: [PATCH 2/3] Efficient reset for cross client `table(view)`

Signed-off-by: Andrew Stein <steinlink@gmail.com>
---
 docs/md/explanation/view/advanced.md          |  13 +-
 rust/perspective-client/perspective.proto     |   1 +
 rust/perspective-client/src/rust/client.rs    |  10 +-
 .../src/rust/utils/logging.rs                 |   1 +
 rust/perspective-client/src/rust/view.rs      |  10 +-
 .../src/rust/virtual_server/server.rs         |   3 +-
 rust/perspective-js/test/js/delta.spec.js     |  32 +++
 .../test/js/derived/lifecycle.spec.ts         |  20 ++
 .../test/js/multi_server.spec.js              | 213 ++++++++++++++++++
 .../perspective/tests/core/test_async.py      |   2 +-
 .../perspective/tests/server/test_server.py   |  10 +-
 .../perspective/tests/table/test_ports.py     |   6 +-
 .../perspective/tests/table/test_table.py     |   2 +-
 .../perspective/tests/table/test_view.py      |  67 +++---
 .../src/client/client_async.rs                |  18 +-
 .../cpp/perspective/src/cpp/gnode.cpp         |  26 ++-
 .../cpp/perspective/src/cpp/server.cpp        |   1 +
 .../src/include/perspective/gnode.h           |  10 +-
 18 files changed, 383 insertions(+), 62 deletions(-)

diff --git a/docs/md/explanation/view/advanced.md b/docs/md/explanation/view/advanced.md
index 49014787bc..7a023b4cd8 100644
--- a/docs/md/explanation/view/advanced.md
+++ b/docs/md/explanation/view/advanced.md
@@ -222,7 +222,7 @@ view.remove_update(callback);
 <div class="python">
 
 ```python
-def on_update(port_id, delta):
+def on_update(port_id, delta, reset):
     print("View updated", port_id)
 
 view.on_update(on_update, mode="row")
@@ -233,16 +233,19 @@ view.remove_update(on_update)
 
 When `mode` is set to `"row"`, the callback receives a delta of only the rows
 that changed (as Apache Arrow), which is useful for efficiently synchronizing
-tables across clients.
+tables across clients. The callback also receives `reset`, which is `true` when
+the update step began with `clear()` or `replace()`; the delta is then relative
+to an empty `Table`, so a replica should apply it with `replace()` rather than
+`update()`.
 
 ## Remove Callbacks
 
 Register a callback to be notified whenever rows are removed from the underlying
 `Table` by `remove()`, which requires an `index`. The callback receives the
 `port_id` and the removed `index` column values as an Apache Arrow with one
-column per index column, named after that column. It fires once per update step, only for rows which
-existed before that step; `replace()` reports the keys it does not re-supply,
-and `clear()` reports every key:
+column per index column, named after that column. It fires once per update step,
+only for rows which existed before that step; `replace()` reports the keys it
+does not re-supply, and `clear()` reports every key:
 
 <div class="javascript">
 
diff --git a/rust/perspective-client/perspective.proto b/rust/perspective-client/perspective.proto
index 3538cda304..27fb29c6db 100644
--- a/rust/perspective-client/perspective.proto
+++ b/rust/perspective-client/perspective.proto
@@ -515,6 +515,7 @@ message ViewOnUpdateReq {
 message ViewOnUpdateResp {
     optional bytes delta = 1;
     uint32 port_id = 2;
+    bool reset = 3;
 }
 
 message ViewOnDeleteReq {}
diff --git a/rust/perspective-client/src/rust/client.rs b/rust/perspective-client/src/rust/client.rs
index 8497d13969..41adae37dc 100644
--- a/rust/perspective-client/src/rust/client.rs
+++ b/rust/perspective-client/src/rust/client.rs
@@ -627,9 +627,13 @@ impl Client {
 
             let table_ = table.clone();
             let callback = asyncfn!(table_, update, async move |update: OnUpdateData| {
-                let update = UpdateData::Arrow(update.delta.expect("Malformed message").into());
-                let options = crate::UpdateOptions::default();
-                table_.update(update, options).await.unwrap_or_log();
+                let data = UpdateData::Arrow(update.delta.expect("Malformed message").into());
+                if update.reset {
+                    table_.replace(data).await.unwrap_or_log();
+                } else {
+                    let options = crate::UpdateOptions::default();
+                    table_.update(data, options).await.unwrap_or_log();
+                }
             });
 
             let options = OnUpdateOptions {
diff --git a/rust/perspective-client/src/rust/utils/logging.rs b/rust/perspective-client/src/rust/utils/logging.rs
index b9cb02d893..6d6ebb53e2 100644
--- a/rust/perspective-client/src/rust/utils/logging.rs
+++ b/rust/perspective-client/src/rust/utils/logging.rs
@@ -145,6 +145,7 @@ impl std::fmt::Display for Response {
                 client_resp: Some(ClientResp::ViewOnUpdateResp(ViewOnUpdateResp {
                     delta: x.delta.as_ref().map(|_| vec![]),
                     port_id: x.port_id,
+                    reset: x.reset,
                 })),
                 ..msg.clone()
             },
diff --git a/rust/perspective-client/src/rust/view.rs b/rust/perspective-client/src/rust/view.rs
index 8a1c235472..7edf5a7d5e 100644
--- a/rust/perspective-client/src/rust/view.rs
+++ b/rust/perspective-client/src/rust/view.rs
@@ -566,16 +566,18 @@ impl View {
 
     /// Register a callback with this [`View`]. Whenever the view's underlying
     /// table emits an update, this callback will be invoked with an object
-    /// containing `port_id`, indicating which port the update fired on, and
+    /// containing `port_id`, indicating which port the update fired on,
+    /// `reset`, which is `true` when the step began with [`Table::clear`] or
+    /// [`Table::replace`] so `delta` is relative to an empty table, and
     /// optionally `delta`, which is the new data that was updated for each
     /// cell or each row.
     ///
     /// # Arguments
     ///
     /// - `on_update` - A callback function invoked on update, which receives an
-    ///   object with two keys: `port_id`, indicating which port the update was
-    ///   triggered on, and `delta`, whose value is dependent on the mode
-    ///   parameter.
+    ///   object with three keys: `port_id`, indicating which port the update
+    ///   was triggered on, `reset`, and `delta`, whose value is dependent on
+    ///   the mode parameter.
     /// - `options` - If this is provided as `OnUpdateOptions { mode:
     ///   Some(OnUpdateMode::Row) }`, then `delta` is an Arrow of the updated
     ///   rows. Otherwise `delta` will be [`Option::None`].
diff --git a/rust/perspective-client/src/rust/virtual_server/server.rs b/rust/perspective-client/src/rust/virtual_server/server.rs
index bc34edb686..a974f14b7b 100644
--- a/rust/perspective-client/src/rust/virtual_server/server.rs
+++ b/rust/perspective-client/src/rust/virtual_server/server.rs
@@ -651,7 +651,8 @@ impl<T: VirtualServerHandler> VirtualServer<T> {
             ViewOnUpdateReq(_) => {
                 respond!(msg, ViewOnUpdateResp {
                     delta: None,
-                    port_id: 0
+                    port_id: 0,
+                    reset: false
                 })
             },
             ViewOnDeleteReq(_) => {
diff --git a/rust/perspective-js/test/js/delta.spec.js b/rust/perspective-js/test/js/delta.spec.js
index b2da4f17e8..898375f47a 100644
--- a/rust/perspective-js/test/js/delta.spec.js
+++ b/rust/perspective-js/test/js/delta.spec.js
@@ -87,6 +87,38 @@ function it_old_behavior(name, capture) {
                 await table.update(partial_change_y);
             });
 
+            test("`reset` marks steps that began with `replace` or `clear`", async function () {
+                const table = await perspective.table(data, { index: "x" });
+                const view = await table.view();
+                const steps = [];
+                let resolve;
+                const next = () =>
+                    new Promise((x) => {
+                        resolve = x;
+                    });
+
+                await view.on_update(
+                    (updated) => {
+                        steps.push(updated.reset);
+                        resolve();
+                    },
+                    { mode: "row" },
+                );
+
+                let promise = next();
+                await table.update(partial_change_y);
+                await promise;
+                promise = next();
+                await table.replace(data);
+                await promise;
+                promise = next();
+                await table.clear();
+                await promise;
+                expect(steps).toEqual([false, true, true]);
+                await view.delete();
+                await table.delete();
+            });
+
             it_old_behavior(
                 "returns changed rows, hidden sort",
                 async function (done) {
diff --git a/rust/perspective-js/test/js/derived/lifecycle.spec.ts b/rust/perspective-js/test/js/derived/lifecycle.spec.ts
index d94ba3976a..eb5c430d71 100644
--- a/rust/perspective-js/test/js/derived/lifecycle.spec.ts
+++ b/rust/perspective-js/test/js/derived/lifecycle.spec.ts
@@ -119,4 +119,24 @@ test.describe("Derived table lifecycle", function () {
             await source.delete();
         });
     }
+    for (const [name, config] of Object.entries({
+        unit: {},
+        flat: PARENTS.flat,
+    })) {
+        test(`${name}: unindexed parent clear then replace`, async function () {
+            const source = await perspective.table(SCHEMA);
+            await source.update(rows(24));
+            const view = await source.view(config);
+            const derived = await perspective.table(view);
+            await source.clear();
+            await expect_flat_parity(view, derived);
+            await source.update(rows(8, 3));
+            await expect_flat_parity(view, derived);
+            await source.replace(rows(5, 50));
+            await expect_flat_parity(view, derived);
+            await derived.delete();
+            await view.delete();
+            await source.delete();
+        });
+    }
 });
diff --git a/rust/perspective-js/test/js/multi_server.spec.js b/rust/perspective-js/test/js/multi_server.spec.js
index 9a707d1e29..cf2bf2e7cf 100644
--- a/rust/perspective-js/test/js/multi_server.spec.js
+++ b/rust/perspective-js/test/js/multi_server.spec.js
@@ -108,5 +108,218 @@ import perspective from "./perspective_client";
             expect(json0).toEqual([{ x: 3, y: 4 }]);
             expect(json0).toEqual(json1);
         });
+
+        test("Replace transfers to an unindexed remote Table", async function ({
+            page,
+        }) {
+            await page.goto("/rust/perspective-js/test/html/test.html");
+            const [json0, json1] = await page.evaluate(async () => {
+                let perspective = await import(
+                    "http://localhost:6598/node_modules/@perspective-dev/client/dist/cdn/perspective.js"
+                );
+
+                perspective.init_client(
+                    fetch(
+                        "http://localhost:6598/node_modules/@perspective-dev/client/dist/wasm/perspective-js.wasm",
+                    ),
+                );
+
+                const settle = async (a, b) => {
+                    for (let i = 0; i < 50; i++) {
+                        const [x, y] = await Promise.all([
+                            a.to_json(),
+                            b.to_json(),
+                        ]);
+                        if (JSON.stringify(x) === JSON.stringify(y)) {
+                            return;
+                        }
+
+                        await new Promise((resolve) =>
+                            setTimeout(resolve, 100),
+                        );
+                    }
+                };
+
+                const worker0 = await perspective.worker();
+                const worker1 = await perspective.worker();
+                const table0 = await worker0.table("x,y\n1,2\n3,4");
+                const view0 = await table0.view();
+                const table1 = await worker1.table(view0);
+                const view1 = await table1.view();
+                await table0.replace([
+                    { x: 5, y: 6 },
+                    { x: 7, y: 8 },
+                ]);
+
+                await settle(view0, view1);
+                return [await view0.to_json(), await view1.to_json()];
+            });
+
+            expect(json0).toEqual([
+                { x: 5, y: 6 },
+                { x: 7, y: 8 },
+            ]);
+
+            expect(json1).toEqual(json0);
+        });
+
+        test("Clear transfers to an unindexed remote Table", async function ({
+            page,
+        }) {
+            await page.goto("/rust/perspective-js/test/html/test.html");
+            const [json0, json1] = await page.evaluate(async () => {
+                let perspective = await import(
+                    "http://localhost:6598/node_modules/@perspective-dev/client/dist/cdn/perspective.js"
+                );
+
+                perspective.init_client(
+                    fetch(
+                        "http://localhost:6598/node_modules/@perspective-dev/client/dist/wasm/perspective-js.wasm",
+                    ),
+                );
+
+                const settle = async (a, b) => {
+                    for (let i = 0; i < 50; i++) {
+                        const [x, y] = await Promise.all([
+                            a.to_json(),
+                            b.to_json(),
+                        ]);
+                        if (JSON.stringify(x) === JSON.stringify(y)) {
+                            return;
+                        }
+
+                        await new Promise((resolve) =>
+                            setTimeout(resolve, 100),
+                        );
+                    }
+                };
+
+                const worker0 = await perspective.worker();
+                const worker1 = await perspective.worker();
+                const table0 = await worker0.table("x,y\n1,2\n3,4");
+                const view0 = await table0.view();
+                const table1 = await worker1.table(view0);
+                const view1 = await table1.view();
+                await table0.clear();
+                await settle(view0, view1);
+                return [await view0.to_json(), await view1.to_json()];
+            });
+
+            expect(json0).toEqual([]);
+            expect(json1).toEqual([]);
+        });
+
+        test("Replace transfers to a remote Table whose View omits the index", async function ({
+            page,
+        }) {
+            await page.goto("/rust/perspective-js/test/html/test.html");
+            const [json0, json1] = await page.evaluate(async () => {
+                let perspective = await import(
+                    "http://localhost:6598/node_modules/@perspective-dev/client/dist/cdn/perspective.js"
+                );
+
+                perspective.init_client(
+                    fetch(
+                        "http://localhost:6598/node_modules/@perspective-dev/client/dist/wasm/perspective-js.wasm",
+                    ),
+                );
+
+                const settle = async (a, b) => {
+                    for (let i = 0; i < 50; i++) {
+                        const [x, y] = await Promise.all([
+                            a.to_json(),
+                            b.to_json(),
+                        ]);
+                        if (JSON.stringify(x) === JSON.stringify(y)) {
+                            return;
+                        }
+
+                        await new Promise((resolve) =>
+                            setTimeout(resolve, 100),
+                        );
+                    }
+                };
+
+                const worker0 = await perspective.worker();
+                const worker1 = await perspective.worker();
+                const table0 = await worker0.table("x,y\n1,2\n3,4", {
+                    index: "x",
+                });
+
+                const view0 = await table0.view({ columns: ["y"] });
+                const table1 = await worker1.table(view0);
+                const view1 = await table1.view();
+                await table0.replace([{ x: 1, y: 20 }]);
+                await settle(view0, view1);
+                return [await view0.to_json(), await view1.to_json()];
+            });
+
+            expect(json0).toEqual([{ y: 20 }]);
+            expect(json1).toEqual(json0);
+        });
+
+        test("Replace and clear transfer to an indexed remote Table", async function ({
+            page,
+        }) {
+            await page.goto("/rust/perspective-js/test/html/test.html");
+            const [json0, json1] = await page.evaluate(async () => {
+                let perspective = await import(
+                    "http://localhost:6598/node_modules/@perspective-dev/client/dist/cdn/perspective.js"
+                );
+
+                perspective.init_client(
+                    fetch(
+                        "http://localhost:6598/node_modules/@perspective-dev/client/dist/wasm/perspective-js.wasm",
+                    ),
+                );
+
+                const settle = async (a, b) => {
+                    for (let i = 0; i < 50; i++) {
+                        const [x, y] = await Promise.all([
+                            a.to_json(),
+                            b.to_json(),
+                        ]);
+                        if (JSON.stringify(x) === JSON.stringify(y)) {
+                            return;
+                        }
+
+                        await new Promise((resolve) =>
+                            setTimeout(resolve, 100),
+                        );
+                    }
+                };
+
+                const worker0 = await perspective.worker();
+                const worker1 = await perspective.worker();
+                const table0 = await worker0.table("x,y\n1,2\n3,4", {
+                    index: "x",
+                });
+
+                const view0 = await table0.view();
+                const table1 = await worker1.table(view0);
+                const view1 = await table1.view();
+                await table0.replace([
+                    { x: 3, y: 40 },
+                    { x: 5, y: 6 },
+                ]);
+
+                await settle(view0, view1);
+                const replaced = [await view0.to_json(), await view1.to_json()];
+                await table0.clear();
+                await settle(view0, view1);
+                return [
+                    replaced,
+                    [await view0.to_json(), await view1.to_json()],
+                ];
+            });
+
+            expect(json0[0]).toEqual([
+                { x: 3, y: 40 },
+                { x: 5, y: 6 },
+            ]);
+
+            expect(json0[1]).toEqual(json0[0]);
+            expect(json1).toEqual([[], []]);
+        });
     });
 })(perspective);
diff --git a/rust/perspective-python/perspective/tests/core/test_async.py b/rust/perspective-python/perspective/tests/core/test_async.py
index 4c4f3b2444..8ca7091af4 100644
--- a/rust/perspective-python/perspective/tests/core/test_async.py
+++ b/rust/perspective-python/perspective/tests/core/test_async.py
@@ -265,7 +265,7 @@ def call_loop(fn, *args):
         view = tbl.view()
         tbl2 = client.table(view.to_arrow())
 
-        def _update(port_id, delta):
+        def _update(port_id, delta, reset):
             print("Updating tbl2", delta)
             tbl2.update(delta)
 
diff --git a/rust/perspective-python/perspective/tests/server/test_server.py b/rust/perspective-python/perspective/tests/server/test_server.py
index d238ef7468..ef132022f5 100644
--- a/rust/perspective-python/perspective/tests/server/test_server.py
+++ b/rust/perspective-python/perspective/tests/server/test_server.py
@@ -425,7 +425,7 @@ def test_server_create_view_and_update_table(self):
     def test_server_on_update_rows(self, sentinel):
         s = sentinel(0)
 
-        def update_callback(port_id, delta):
+        def update_callback(port_id, delta, reset):
             table = Table(delta)
             assert table.size() == 1
             assert table.schema() == {"a": "integer", "b": "string"}
@@ -459,7 +459,7 @@ def update_callback(*args, **kwargs):
     def test_server_on_update_rows_with_port_id(self, sentinel):
         s = sentinel(0)
 
-        def update_callback(port_id, delta):
+        def update_callback(port_id, delta, reset):
             table = Table(delta)
             assert table.size() == 1
             assert table.schema() == {"a": "integer", "b": "string"}
@@ -525,7 +525,7 @@ def update_callback(port_id, delta):
     def test_server_remove_update(self, sentinel):
         s = sentinel(0)
 
-        def update_callback(port_id, delta):
+        def update_callback(port_id, delta, reset):
             s.set(s.get() + 1)
 
         # create a table and view using client
@@ -706,7 +706,7 @@ def post_update(msg, binary=False):
     def test_server_on_update_rows_with_port_id_through_wire_API(self, sentinel):
         s = sentinel(0)
 
-        def update_callback(port_id, delta):
+        def update_callback(port_id, delta, reset):
             table = Table(delta)
             assert table.size() == 1
             assert table.schema() == {"a": "integer", "b": "string"}
@@ -808,7 +808,7 @@ def post_update(msg, binary=False):
     def test_server_remove_update_through_wire_API(self, sentinel):
         s = sentinel(0)
 
-        def update_callback(port_id, delta):
+        def update_callback(port_id, delta, reset):
             s.set(s.get() + 1)
 
         # create a table and view using client
diff --git a/rust/perspective-python/perspective/tests/table/test_ports.py b/rust/perspective-python/perspective/tests/table/test_ports.py
index 1e907d0b84..0953fca648 100644
--- a/rust/perspective-python/perspective/tests/table/test_ports.py
+++ b/rust/perspective-python/perspective/tests/table/test_ports.py
@@ -106,7 +106,7 @@ def test_ports_should_have_unique_deltas(self):
             port: [{"a": port, "b": str(port), "c": True}] for port in ports_to_update
         }
 
-        def callback(port_id, delta):
+        def callback(port_id, delta, reset):
             assert port_id in ports_to_update
             _t = Table(delta)
             _v = _t.view()
@@ -157,13 +157,13 @@ def test_ports_multiple_tables_with_different_ports(self):
 
         # when the client updates, check whether the port id matches that
         # of the server, and complete the test.
-        def client_callback(port_id, delta):
+        def client_callback(port_id, delta, reset):
             if port_id == client_port:
                 print("UPDATING SERVER")
                 server.update(delta, port_id=server_port_for_client)
 
         # when the server updates, pass the update back to the client
-        def server_callback(port_id, delta):
+        def server_callback(port_id, delta, reset):
             print("UPDATING CLIENT")
             assert port_id == server_port_for_client
             assert server.size() == 8
diff --git a/rust/perspective-python/perspective/tests/table/test_table.py b/rust/perspective-python/perspective/tests/table/test_table.py
index 1edb245512..08aefd937e 100644
--- a/rust/perspective-python/perspective/tests/table/test_table.py
+++ b/rust/perspective-python/perspective/tests/table/test_table.py
@@ -672,7 +672,7 @@ def test_table_replace_should_fire_on_update_with_delta(self, sentinel):
 
         s = sentinel(False)
 
-        def updater(port_id, delta):
+        def updater(port_id, delta, reset):
             # assert port_id == 0
             table2 = Table(delta)
             assert table2.view().to_records() == data2
diff --git a/rust/perspective-python/perspective/tests/table/test_view.py b/rust/perspective-python/perspective/tests/table/test_view.py
index 7532b7e412..5919683564 100644
--- a/rust/perspective-python/perspective/tests/table/test_view.py
+++ b/rust/perspective-python/perspective/tests/table/test_view.py
@@ -876,7 +876,7 @@ def test_view_variance_multi_update_delta(self):
         # 2 here should result in null var because the group size is 1
         update_data = {"a": [15.12, 9.102, 0.99, 12.8], "b": [1, 0, 1, 2]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             table2 = Table(delta)
             view2 = table2.view()
             result = view2.to_columns()
@@ -1025,7 +1025,7 @@ def test_view_variance_multi_update_indexed_delta(self):
             "c": [0, 4, 1, 6],
         }
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             table2 = Table(delta)
             view2 = table2.view()
             result = view2.to_columns()
@@ -1236,7 +1236,7 @@ def test_view_standard_deviation_multi_update_delta(self):
         # 2 here should result in null stddev because the group size is 1
         update_data = {"a": [15.12, 9.102, 0.99, 12.8], "b": [1, 0, 1, 2]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             table2 = Table(delta)
             view2 = table2.view()
             result = view2.to_columns()
@@ -1385,7 +1385,7 @@ def test_view_standard_deviation_multi_update_indexed_delta(self):
             "c": [0, 4, 1, 6],
         }
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             table2 = Table(delta)
             view2 = table2.view()
             result = view2.to_columns()
@@ -1931,7 +1931,7 @@ def test_view_row_delta_zero(self, util):
         data = [{"a": 1, "b": 2}, {"a": 3, "b": 4}]
         update_data = {"a": [5], "b": [6]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(delta, update_data)
 
         tbl = Table(data)
@@ -1939,11 +1939,26 @@ def cb1(port_id, delta):
         view.on_update(cb1, mode="row")
         tbl.update(update_data)
 
+    def test_view_row_delta_reset_flag(self):
+        data = [{"a": 1, "b": 2}, {"a": 3, "b": 4}]
+        steps = []
+
+        def cb1(port_id, delta, reset):
+            steps.append(reset)
+
+        tbl = Table(data, index="a")
+        view = tbl.view()
+        view.on_update(cb1, mode="row")
+        tbl.update([{"a": 1, "b": 5}])
+        tbl.replace(data)
+        tbl.clear()
+        assert steps == [False, True, True]
+
     def test_view_row_delta_zero_column_subset(self, util):
         data = [{"a": 1, "b": 2}, {"a": 3, "b": 4}]
         update_data = {"a": [5], "b": [6]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(delta, {"b": [6]})
 
         tbl = Table(data)
@@ -1954,7 +1969,7 @@ def cb1(port_id, delta):
     def test_view_row_delta_zero_from_schema(self, util):
         update_data = {"a": [5], "b": [6]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(delta, update_data)
 
         tbl = Table({"a": "integer", "b": "integer"})
@@ -1965,7 +1980,7 @@ def cb1(port_id, delta):
     def test_view_row_delta_zero_from_schema_column_subset(self, util):
         update_data = {"a": [5], "b": [6]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(delta, {"b": [6]})
 
         tbl = Table({"a": "integer", "b": "integer"})
@@ -1977,7 +1992,7 @@ def cb1(port_id, delta):
     def test_view_row_delta_zero_from_schema_filtered(self, util):
         update_data = {"a": [8, 9, 10, 11], "b": [1, 2, 3, 4]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(delta, {"a": [11], "b": [4]})
 
         tbl = Table({"a": "integer", "b": "integer"})
@@ -1988,7 +2003,7 @@ def cb1(port_id, delta):
     def test_view_row_delta_zero_from_schema_indexed(self, util):
         update_data = {"a": ["a", "b", "a"], "b": [1, 2, 3]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(delta, {"a": ["a", "b"], "b": [3, 2]})
 
         tbl = Table({"a": "string", "b": "integer"}, index="a")
@@ -2001,7 +2016,7 @@ def cb1(port_id, delta):
     def test_view_row_delta_zero_from_schema_indexed_filtered(self, util):
         update_data = {"a": [8, 9, 10, 11, 11], "b": [1, 2, 3, 4, 5]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(delta, {"a": [11], "b": [5]})
 
         tbl = Table({"a": "integer", "b": "integer"}, index="a")
@@ -2013,7 +2028,7 @@ def test_view_row_delta_one(self, util):
         data = [{"a": 1, "b": 2}, {"a": 3, "b": 4}]
         update_data = {"a": [5], "b": [6]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(delta, {"a": [9, 5], "b": [12, 6]})
 
         tbl = Table(data)
@@ -2029,7 +2044,7 @@ def cb1(port_id, delta):
     def test_view_row_delta_one_from_schema(self, util):
         update_data = {"a": [1, 2, 3, 4, 5], "b": [6, 7, 8, 9, 10]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(delta, {"a": [15, 1, 2, 3, 4, 5], "b": [40, 6, 7, 8, 9, 10]})
 
         tbl = Table({"a": "integer", "b": "integer"})
@@ -2040,7 +2055,7 @@ def cb1(port_id, delta):
     def test_view_row_delta_one_from_schema_sorted(self, util):
         update_data = {"a": [1, 2, 3, 4, 5], "b": [6, 7, 8, 9, 10]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(delta, {"a": [15, 5, 4, 3, 2, 1], "b": [40, 10, 9, 8, 7, 6]})
 
         tbl = Table({"a": "integer", "b": "integer"})
@@ -2051,7 +2066,7 @@ def cb1(port_id, delta):
     def test_view_row_delta_one_from_schema_filtered(self, util):
         update_data = {"a": [1, 2, 3, 4, 5], "b": [6, 7, 8, 9, 10]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(delta, {"a": [9, 4, 5], "b": [19, 9, 10]})
 
         tbl = Table({"a": "integer", "b": "integer"})
@@ -2062,7 +2077,7 @@ def cb1(port_id, delta):
     def test_view_row_delta_one_from_schema_sorted_filtered(self, util):
         update_data = {"a": [1, 2, 3, 4, 5], "b": [6, 7, 8, 9, 10]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(delta, {"a": [9, 5, 4], "b": [19, 10, 9]})
 
         tbl = Table({"a": "integer", "b": "integer"})
@@ -2073,7 +2088,7 @@ def cb1(port_id, delta):
     def test_view_row_delta_one_from_schema_indexed(self, util):
         update_data = {"a": [1, 2, 3, 4, 5, 5, 4], "b": [6, 7, 8, 9, 10, 11, 12]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(delta, {"a": [15, 1, 2, 3, 4, 5], "b": [44, 6, 7, 8, 12, 11]})
 
         tbl = Table({"a": "integer", "b": "integer"}, index="a")
@@ -2086,7 +2101,7 @@ def cb1(port_id, delta):
     def test_view_row_delta_one_from_schema_sorted_indexed(self, util):
         update_data = {"a": [1, 2, 3, 4, 5, 5, 4], "b": [6, 7, 8, 9, 10, 11, 12]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(delta, {"a": [15, 4, 5, 3, 2, 1], "b": [44, 12, 11, 8, 7, 6]})
 
         tbl = Table({"a": "integer", "b": "integer"}, index="a")
@@ -2099,7 +2114,7 @@ def cb1(port_id, delta):
     def test_view_row_delta_one_from_schema_filtered_indexed(self, util):
         update_data = {"a": [1, 2, 3, 4, 5, 5, 4], "b": [6, 7, 8, 9, 10, 11, 12]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(delta, {"a": [9, 4, 5], "b": [23, 12, 11]})
 
         tbl = Table({"a": "integer", "b": "integer"}, index="a")
@@ -2113,7 +2128,7 @@ def test_view_row_delta_two(self, util):
         data = [{"a": 1, "b": 2}, {"a": 3, "b": 4}]
         update_data = {"a": [5], "b": [6]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(
                 delta,
                 {
@@ -2141,7 +2156,7 @@ def cb1(port_id, delta):
     def test_view_row_delta_two_from_schema(self, util):
         data = [{"a": 1, "b": 2}, {"a": 3, "b": 4}]
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(
                 delta,
                 {
@@ -2160,7 +2175,7 @@ def cb1(port_id, delta):
     def test_view_row_delta_two_from_schema_indexed(self, util):
         data = [{"a": 1, "b": 2}, {"a": 3, "b": 4}, {"a": 3, "b": 5}]
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(
                 delta,
                 {
@@ -2180,7 +2195,7 @@ def test_view_row_delta_two_column_only(self, util):
         data = [{"a": 1, "b": 2}, {"a": 3, "b": 4}]
         update_data = {"a": [5], "b": [6]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(
                 delta,
                 {
@@ -2208,7 +2223,7 @@ def test_view_row_delta_two_column_only_indexed(self, util):
         data = [{"a": 1, "b": 2}, {"a": 3, "b": 4}, {"a": 3, "b": 5}]
         update_data = {"a": [5], "b": [6]}
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(
                 delta,
                 {
@@ -2235,7 +2250,7 @@ def cb1(port_id, delta):
     def test_view_row_delta_two_column_only_from_schema(self, util):
         data = [{"a": 1, "b": 2}, {"a": 3, "b": 4}]
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(
                 delta,
                 {
@@ -2254,7 +2269,7 @@ def cb1(port_id, delta):
     def test_view_row_delta_two_column_only_from_schema_indexed(self, util):
         data = [{"a": 1, "b": 2}, {"a": 3, "b": 4}, {"a": 3, "b": 5}]
 
-        def cb1(port_id, delta):
+        def cb1(port_id, delta, reset):
             compare_delta(
                 delta,
                 {
diff --git a/rust/perspective-python/src/client/client_async.rs b/rust/perspective-python/src/client/client_async.rs
index 2dad3c0455..1301fb2f36 100644
--- a/rust/perspective-python/src/client/client_async.rs
+++ b/rust/perspective-python/src/client/client_async.rs
@@ -963,17 +963,17 @@ impl AsyncView {
     }
 
     /// Register a callback with this [`View`]. Whenever the view's underlying
-    /// table emits an update, this callback will be invoked with an object
-    /// containing `port_id`, indicating which port the update fired on, and
-    /// optionally `delta`, which is the new data that was updated for each
-    /// cell or each row.
+    /// table emits an update, this callback will be invoked with `port_id`,
+    /// indicating which port the update fired on, and in `"row"` mode also
+    /// with `delta`, the new data that was updated for each row, and `reset`,
+    /// which is `True` when the step began with `clear()` or `replace()` so
+    /// `delta` is relative to an empty table.
     ///
     /// # Arguments
     ///
-    /// - `on_update` - A callback function invoked on update, which receives an
-    ///   object with two keys: `port_id`, indicating which port the update was
-    ///   triggered on, and `delta`, whose value is dependent on the mode
-    ///   parameter.
+    /// - `on_update` - A callback function invoked on update, which receives
+    ///   `port_id`, indicating which port the update was triggered on, and in
+    ///   `"row"` mode `delta` and `reset`.
     /// - `options` - If this is provided as `OnUpdateOptions { mode:
     ///   Some(OnUpdateMode::Row) }`, then `delta` is an Arrow of the updated
     ///   rows. Otherwise `delta` will be [`Option::None`].
@@ -988,7 +988,7 @@ impl AsyncView {
                         match &x.delta {
                             None => callback.call1(py, (x.port_id,))?,
                             Some(delta) => {
-                                callback.call1(py, (x.port_id, PyBytes::new(py, delta)))?
+                                callback.call1(py, (x.port_id, PyBytes::new(py, delta), x.reset))?
                             },
                         };
 
diff --git a/rust/perspective-server/cpp/perspective/src/cpp/gnode.cpp b/rust/perspective-server/cpp/perspective/src/cpp/gnode.cpp
index 3c41f942e1..f2afb1db0d 100644
--- a/rust/perspective-server/cpp/perspective/src/cpp/gnode.cpp
+++ b/rust/perspective-server/cpp/perspective/src/cpp/gnode.cpp
@@ -337,13 +337,16 @@ t_gnode::_process_mask_existed_rows(t_process_state& process_state) {
 
 void
 t_gnode::_take_reset_removes(
-    const t_column* pkey_col, t_uindex flattened_num_rows
+    const t_column* pkey_col,
+    const t_column* op_col,
+    t_uindex flattened_num_rows
 ) {
     if (!m_reset_pending) {
         return;
     }
 
     m_reset_pending = false;
+    m_was_reset = true;
     if (!m_reset_pkeys) {
         return;
     }
@@ -351,6 +354,10 @@ t_gnode::_take_reset_removes(
     tsl::hopscotch_set<t_tscalar> incoming;
     incoming.reserve(flattened_num_rows);
     for (t_uindex idx = 0; idx < flattened_num_rows; ++idx) {
+        if (*(op_col->get_nth<std::uint8_t>(idx)) == OP_DELETE) {
+            continue;
+        }
+
         incoming.insert(pkey_col->get_scalar(idx));
     }
 
@@ -609,6 +616,7 @@ t_gnode::_process_table(t_uindex port_id) {
         }
 
         m_reset_pending = false;
+        m_was_reset = true;
         m_removed_pkeys = std::move(m_reset_pkeys);
         m_reset_pkeys = nullptr;
         m_was_updated = true;
@@ -633,7 +641,9 @@ t_gnode::_process_table(t_uindex port_id) {
         row_lookup[idx] = m_gstate->lookup(pkey);
     }
 
-    _take_reset_removes(pkey_col, flattened_num_rows);
+    _take_reset_removes(
+        pkey_col, flattened->_get_const_column("psp_op"), flattened_num_rows
+    );
 
     // first update - master table is empty
     if (m_gstate->mapping_size() == 0) {
@@ -895,6 +905,7 @@ t_gnode::process_derived(const t_derived_step& step) {
     PSP_TRACE_SENTINEL();
     PSP_VERBOSE_ASSERT(m_init, "Cannot `process_derived` on an uninited gnode.");
     m_was_updated = false;
+    m_was_reset = false;
     m_removed_pkeys = nullptr;
 
     const std::shared_ptr<t_data_table>& flattened = step.m_flattened;
@@ -905,6 +916,7 @@ t_gnode::process_derived(const t_derived_step& step) {
         }
 
         m_reset_pending = false;
+        m_was_reset = true;
         m_removed_pkeys = std::move(m_reset_pkeys);
         m_reset_pkeys = nullptr;
         m_was_updated = true;
@@ -923,7 +935,9 @@ t_gnode::process_derived(const t_derived_step& step) {
         identity_lookup[idx] = t_rlookup(idx, exists);
     }
 
-    _take_reset_removes(pkey_col, flattened_num_rows);
+    _take_reset_removes(
+        pkey_col, flattened->_get_const_column("psp_op"), flattened_num_rows
+    );
 
     if (m_gstate->mapping_size() == 0) {
         m_gstate->commit_derived(flattened, step.m_rows);
@@ -2105,6 +2119,7 @@ t_gnode::clear_output_ports() {
         m_oport->get_table()->clear();
     }
     m_removed_pkeys = nullptr;
+    m_was_reset = false;
 }
 
 std::shared_ptr<t_data_table>
@@ -2112,6 +2127,11 @@ t_gnode::get_removed_pkeys() const {
     return m_removed_pkeys;
 }
 
+bool
+t_gnode::get_was_reset() const {
+    return m_was_reset;
+}
+
 void
 t_gnode::set_removes_enabled(bool enabled) {
     m_removes_enabled = enabled;
diff --git a/rust/perspective-server/cpp/perspective/src/cpp/server.cpp b/rust/perspective-server/cpp/perspective/src/cpp/server.cpp
index f0fb4229d5..6f17aacbed 100644
--- a/rust/perspective-server/cpp/perspective/src/cpp/server.cpp
+++ b/rust/perspective-server/cpp/perspective/src/cpp/server.cpp
@@ -4088,6 +4088,7 @@ ProtoServer::_notify_table(
             out.set_entity_id(view_id);
             auto* r = out.mutable_view_on_update_resp();
             r->set_port_id(port_id);
+            r->set_reset(table->get_gnode()->get_was_reset());
             if (view->get_deltas_enabled()) {
                 *r->mutable_delta() = *view->get_row_delta_as_arrow();
             }
diff --git a/rust/perspective-server/cpp/perspective/src/include/perspective/gnode.h b/rust/perspective-server/cpp/perspective/src/include/perspective/gnode.h
index bbeb1450ae..abd705030e 100644
--- a/rust/perspective-server/cpp/perspective/src/include/perspective/gnode.h
+++ b/rust/perspective-server/cpp/perspective/src/include/perspective/gnode.h
@@ -172,6 +172,11 @@ class PERSPECTIVE_EXPORT t_gnode {
      */
     std::shared_ptr<t_data_table> get_removed_pkeys() const;
 
+    /**
+     * @brief Whether the most recent step consumed a pending `reset()`.
+     */
+    bool get_was_reset() const;
+
     void set_removes_enabled(bool enabled);
     bool get_removes_enabled() const;
 
@@ -355,7 +360,9 @@ class PERSPECTIVE_EXPORT t_gnode {
      * `pkey_col` as removed.
      */
     void _take_reset_removes(
-        const t_column* pkey_col, t_uindex flattened_num_rows
+        const t_column* pkey_col,
+        const t_column* op_col,
+        t_uindex flattened_num_rows
     );
 
     t_mask _compute_transitions(
@@ -482,6 +489,7 @@ class PERSPECTIVE_EXPORT t_gnode {
     bool m_was_updated;
     bool m_removes_enabled = false;
     bool m_reset_pending = false;
+    bool m_was_reset = false;
     std::shared_ptr<t_data_table> m_removed_pkeys;
     std::shared_ptr<t_data_table> m_reset_pkeys;
 

From d99be52b0d9607fd0b22da0bc069e124c58958e4 Mon Sep 17 00:00:00 2001
From: Andrew Stein <steinlink@gmail.com>
Date: Thu, 5 Nov 2026 04:29:39 -0500
Subject: [PATCH 3/3] Streamline migrations

Signed-off-by: Andrew Stein <steinlink@gmail.com>
---
 Cargo.lock                                    |   9 --
 Cargo.toml                                    |   1 -
 docs/md/how_to/rust/migrate.md                |   2 +-
 rust/perspective-js/build.mjs                 |   6 +-
 .../src/ts/perspective.browser.ts             |   2 +-
 rust/perspective-js/src/ts/perspective.cdn.ts |   2 +-
 .../perspective-js/src/ts/perspective.node.ts |   2 +-
 rust/perspective-js/src/ts/wasm/migrate.ts    |   4 +-
 rust/perspective-js/src/ts/wasm/registry.ts   |   4 +-
 rust/perspective-js/test/js/cdn_url.spec.ts   | 135 ------------------
 .../test/js/multi_server.spec.js              | 130 ++++++++++-------
 rust/perspective-js/test/js/registry.spec.js  |   2 +-
 rust/perspective-migrate-js/Cargo.toml        |  33 -----
 rust/perspective-migrate-js/src/lib.rs        |  41 ------
 rust/perspective-migrate/Cargo.toml           |   3 +
 rust/perspective-migrate/src/lib.rs           |  28 ++++
 rust/perspective-viewer/src/ts/bootstrap.ts   |   2 +-
 .../src/ts/perspective-viewer.cdn.ts          |   2 +-
 .../restore_workspace_layout.spec.ts          |   6 +-
 19 files changed, 128 insertions(+), 286 deletions(-)
 delete mode 100644 rust/perspective-js/test/js/cdn_url.spec.ts
 delete mode 100644 rust/perspective-migrate-js/Cargo.toml
 delete mode 100644 rust/perspective-migrate-js/src/lib.rs

diff --git a/Cargo.lock b/Cargo.lock
index 42e2614fb4..74bdab38bb 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2016,15 +2016,6 @@ version = "5.6.1"
 dependencies = [
  "perspective-client",
  "serde",
- "serde_json",
-]
-
-[[package]]
-name = "perspective-migrate-js"
-version = "5.6.1"
-dependencies = [
- "perspective-migrate",
- "serde",
  "serde-wasm-bindgen",
  "serde_json",
  "wasm-bindgen",
diff --git a/Cargo.toml b/Cargo.toml
index 39b8633aa7..4d5741b820 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -28,7 +28,6 @@ members = [
     "rust/perspective-client",
     "rust/perspective-js",
     "rust/perspective-migrate",
-    "rust/perspective-migrate-js",
     "rust/perspective-python",
     "rust/perspective-server",
     "rust/perspective-viewer",
diff --git a/docs/md/how_to/rust/migrate.md b/docs/md/how_to/rust/migrate.md
index 748fa52859..4ced98c459 100644
--- a/docs/md/how_to/rust/migrate.md
+++ b/docs/md/how_to/rust/migrate.md
@@ -43,7 +43,7 @@ await viewer.restoreWorkspace(value);
 ```
 
 `MIGRATE_WASM` is
-`@perspective-dev/client/dist/wasm/perspective-migrate-js.wasm`. In Node.js,
+`@perspective-dev/client/dist/wasm/perspective-migrate.wasm`. In Node.js,
 `perspective.migrate()` needs no registration.
 
 ```python
diff --git a/rust/perspective-js/build.mjs b/rust/perspective-js/build.mjs
index bf696e7d0b..009b3ce362 100644
--- a/rust/perspective-js/build.mjs
+++ b/rust/perspective-js/build.mjs
@@ -140,13 +140,13 @@ async function build_rust() {
     );
 
     execSync(
-        `PSP_ROOT_DIR=../.. cargo bundle --target=${get_host()} -- perspective_migrate_js ${release_flag} --no-tracing`,
+        `PSP_ROOT_DIR=../.. cargo bundle --target=${get_host()} -- perspective_migrate ${release_flag} --no-tracing`,
         INHERIT,
     );
 
     await compress(
-        "dist/wasm/perspective-migrate-js.wasm",
-        "dist/wasm/perspective-migrate-js.wasm",
+        "dist/wasm/perspective-migrate.wasm",
+        "dist/wasm/perspective-migrate.wasm",
     );
 }
 
diff --git a/rust/perspective-js/src/ts/perspective.browser.ts b/rust/perspective-js/src/ts/perspective.browser.ts
index 8e75499c5f..d6431aa0f5 100644
--- a/rust/perspective-js/src/ts/perspective.browser.ts
+++ b/rust/perspective-js/src/ts/perspective.browser.ts
@@ -152,7 +152,7 @@ function is_wasm_source(
  * perspective.init_server({
  *     wasm32: () => fetch("perspective-server.wasm"),
  *     wasm64: () => fetch("perspective-server.memory64.wasm"),
- *     migrate: () => fetch("perspective-migrate-js.wasm"),
+ *     migrate: () => fetch("perspective-migrate.wasm"),
  * });
  * ```
  */
diff --git a/rust/perspective-js/src/ts/perspective.cdn.ts b/rust/perspective-js/src/ts/perspective.cdn.ts
index d0d7d3851f..124886212e 100644
--- a/rust/perspective-js/src/ts/perspective.cdn.ts
+++ b/rust/perspective-js/src/ts/perspective.cdn.ts
@@ -27,7 +27,7 @@ register_default({
             ),
         ),
     migrate: () =>
-        fetch(new URL("../wasm/perspective-migrate-js.wasm", import.meta.url)),
+        fetch(new URL("../wasm/perspective-migrate.wasm", import.meta.url)),
 });
 
 export default perspective;
diff --git a/rust/perspective-js/src/ts/perspective.node.ts b/rust/perspective-js/src/ts/perspective.node.ts
index 35b80afde8..23554c1a8d 100644
--- a/rust/perspective-js/src/ts/perspective.node.ts
+++ b/rust/perspective-js/src/ts/perspective.node.ts
@@ -86,7 +86,7 @@ await perspective_client.default({ module_or_path: uncompressed_client_wasm });
 const MIGRATE = new MigrateLoader();
 MIGRATE.register(async () => {
     const buffer = await fs.readFile(
-        path.join(__dirname, "../../dist/wasm/perspective-migrate-js.wasm"),
+        path.join(__dirname, "../../dist/wasm/perspective-migrate.wasm"),
     );
 
     return await load_wasm_stage_0(buffer.buffer as ArrayBuffer);
diff --git a/rust/perspective-js/src/ts/wasm/migrate.ts b/rust/perspective-js/src/ts/wasm/migrate.ts
index d108bc3762..09f40ae457 100644
--- a/rust/perspective-js/src/ts/wasm/migrate.ts
+++ b/rust/perspective-js/src/ts/wasm/migrate.ts
@@ -10,7 +10,7 @@
 // ┃ of the [Apache License 2.0](https://www.apache.org/licenses/LICENSE-2.0). ┃
 // ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
 
-import * as migrate_wasm from "../../../dist/wasm/perspective-migrate-js.js";
+import * as migrate_wasm from "../../../dist/wasm/perspective-migrate.js";
 
 /**
  * The kind of persisted config `migrate()` upgrades: an engine `ViewConfig`,
@@ -57,7 +57,7 @@ export class MigrateLoader {
     ): Promise<MigrateResult<T>> {
         if (this.module === undefined) {
             if (this.source === undefined) {
-                throw new Error("Missing perspective-migrate-js.wasm");
+                throw new Error("Missing perspective-migrate.wasm");
             }
 
             const source = this.source;
diff --git a/rust/perspective-js/src/ts/wasm/registry.ts b/rust/perspective-js/src/ts/wasm/registry.ts
index f0409f2c90..724c933137 100644
--- a/rust/perspective-js/src/ts/wasm/registry.ts
+++ b/rust/perspective-js/src/ts/wasm/registry.ts
@@ -345,7 +345,7 @@ export function register(
  * - `wasm` - Binaries by role: `client` (`perspective-js.wasm`), `viewer`
  *   (`perspective-viewer.wasm`, which also backs every `Client`), `server`
  *   (one engine build) or `server32` / `server64` (selected by Memory64
- *   support), and `migrate` (`perspective-migrate-js.wasm`).
+ *   support), and `migrate` (`perspective-migrate.wasm`).
  * - `options` - `disable_stage_0` skips decompression for these sources.
  *
  * # Examples
@@ -500,7 +500,7 @@ export function resolve_migrate(): Promise<ArrayBuffer | WebAssembly.Module> {
         if (entry === undefined) {
             return Promise.reject(
                 new Error(
-                    "Missing perspective-migrate-js.wasm: register `migrate` with init()",
+                    "Missing perspective-migrate.wasm: register `migrate` with init()",
                 ),
             );
         }
diff --git a/rust/perspective-js/test/js/cdn_url.spec.ts b/rust/perspective-js/test/js/cdn_url.spec.ts
deleted file mode 100644
index 1afa1ce160..0000000000
--- a/rust/perspective-js/test/js/cdn_url.spec.ts
+++ /dev/null
@@ -1,135 +0,0 @@
-// ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
-// ┃ ██████ ██████ ██████       █      █      █      █      █ █▄  ▀███ █       ┃
-// ┃ ▄▄▄▄▄█ █▄▄▄▄▄ ▄▄▄▄▄█  ▀▀▀▀▀█▀▀▀▀▀ █ ▀▀▀▀▀█ ████████▌▐███ ███▄  ▀█ █ ▀▀▀▀▀ ┃
-// ┃ █▀▀▀▀▀ █▀▀▀▀▀ █▀██▀▀ ▄▄▄▄▄ █ ▄▄▄▄▄█ ▄▄▄▄▄█ ████████▌▐███ █████▄   █ ▄▄▄▄▄ ┃
-// ┃ █      ██████ █  ▀█▄       █ ██████      █      ███▌▐███ ███████▄ █       ┃
-// ┣━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┫
-// ┃ Copyright (c) 2017, the Perspective Authors.                              ┃
-// ┃ ╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌ ┃
-// ┃ This file is part of the Perspective library, distributed under the terms ┃
-// ┃ of the [Apache License 2.0](https://www.apache.org/licenses/LICENSE-2.0). ┃
-// ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
-
-import { test, expect } from "@perspective-dev/test";
-import {
-    resolve_package_wasm_url,
-    resolve_server_wasm_url,
-} from "../../src/ts/wasm/cdn.ts";
-
-test.describe("resolve_server_wasm_url", function () {
-    test("preserves exact version tags on jsdelivr URLs", function () {
-        expect(
-            resolve_server_wasm_url(
-                "https://cdn.jsdelivr.net/npm/@perspective-dev/client@4.5.1/dist/cdn/perspective.js",
-            ),
-        ).toEqual(
-            "https://cdn.jsdelivr.net/npm/@perspective-dev/server@4.5.1/dist/wasm/perspective-server.wasm",
-        );
-    });
-
-    test("preserves range and dist-tag aliases", function () {
-        expect(
-            resolve_server_wasm_url(
-                "https://cdn.jsdelivr.net/npm/@perspective-dev/client@4/dist/cdn/perspective.js",
-            ),
-        ).toEqual(
-            "https://cdn.jsdelivr.net/npm/@perspective-dev/server@4/dist/wasm/perspective-server.wasm",
-        );
-
-        expect(
-            resolve_server_wasm_url(
-                "https://cdn.jsdelivr.net/npm/@perspective-dev/client@latest/dist/cdn/perspective.js",
-            ),
-        ).toEqual(
-            "https://cdn.jsdelivr.net/npm/@perspective-dev/server@latest/dist/wasm/perspective-server.wasm",
-        );
-    });
-
-    test("resolves alternate binaries with the version tag preserved", function () {
-        expect(
-            resolve_server_wasm_url(
-                "https://cdn.jsdelivr.net/npm/@perspective-dev/client@4.5.1/dist/cdn/perspective.js",
-                "perspective-server.memory64.wasm",
-            ),
-        ).toEqual(
-            "https://cdn.jsdelivr.net/npm/@perspective-dev/server@4.5.1/dist/wasm/perspective-server.memory64.wasm",
-        );
-
-        expect(
-            resolve_server_wasm_url(
-                "http://localhost:6598/node_modules/@perspective-dev/client/dist/cdn/perspective.js",
-                "perspective-server.memory64.wasm",
-            ),
-        ).toEqual(
-            "http://localhost:6598/node_modules/@perspective-dev/server/dist/wasm/perspective-server.memory64.wasm",
-        );
-    });
-
-    test("preserves version tags on unpkg URLs", function () {
-        expect(
-            resolve_server_wasm_url(
-                "https://unpkg.com/@perspective-dev/client@4.5.1/dist/cdn/perspective.js",
-            ),
-        ).toEqual(
-            "https://unpkg.com/@perspective-dev/server@4.5.1/dist/wasm/perspective-server.wasm",
-        );
-    });
-
-    test("resolves untagged node_modules layouts to the sibling package", function () {
-        expect(
-            resolve_server_wasm_url(
-                "http://localhost:6598/node_modules/@perspective-dev/client/dist/cdn/perspective.js",
-            ),
-        ).toEqual(
-            "http://localhost:6598/node_modules/@perspective-dev/server/dist/wasm/perspective-server.wasm",
-        );
-    });
-
-    test("matches minified and query-string variants", function () {
-        expect(
-            resolve_server_wasm_url(
-                "https://cdn.jsdelivr.net/npm/@perspective-dev/client@4.5.1/dist/cdn/perspective.min.js?v=1",
-            ),
-        ).toEqual(
-            "https://cdn.jsdelivr.net/npm/@perspective-dev/server@4.5.1/dist/wasm/perspective-server.wasm",
-        );
-    });
-
-    test("falls back to relative resolution for unrecognized layouts", function () {
-        expect(
-            resolve_server_wasm_url(
-                "https://example.com/assets/perspective.js",
-            ),
-        ).toEqual(
-            "https://example.com/server/dist/wasm/perspective-server.wasm",
-        );
-    });
-});
-
-test.describe("resolve_package_wasm_url", function () {
-    test("resolves the client's migrate binary from the viewer bundle", function () {
-        expect(
-            resolve_package_wasm_url(
-                "https://cdn.jsdelivr.net/npm/@perspective-dev/viewer@5.7.0/dist/cdn/perspective-viewer.js",
-                "viewer",
-                "client",
-                "perspective-migrate-js.wasm",
-            ),
-        ).toEqual(
-            "https://cdn.jsdelivr.net/npm/@perspective-dev/client@5.7.0/dist/wasm/perspective-migrate-js.wasm",
-        );
-    });
-
-    test("resolves node_modules layouts to the sibling package", function () {
-        expect(
-            resolve_package_wasm_url(
-                "http://localhost:6598/node_modules/@perspective-dev/viewer/dist/cdn/perspective-viewer.js",
-                "viewer",
-                "client",
-                "perspective-migrate-js.wasm",
-            ),
-        ).toEqual(
-            "http://localhost:6598/node_modules/@perspective-dev/client/dist/wasm/perspective-migrate-js.wasm",
-        );
-    });
-});
diff --git a/rust/perspective-js/test/js/multi_server.spec.js b/rust/perspective-js/test/js/multi_server.spec.js
index cf2bf2e7cf..a8ad73b914 100644
--- a/rust/perspective-js/test/js/multi_server.spec.js
+++ b/rust/perspective-js/test/js/multi_server.spec.js
@@ -124,20 +124,26 @@ import perspective from "./perspective_client";
                     ),
                 );
 
-                const settle = async (a, b) => {
-                    for (let i = 0; i < 50; i++) {
+                const sync = async (view0, view1, action) => {
+                    const { promise, resolve } = Promise.withResolvers();
+                    const token = await view1.on_update(async () => {
                         const [x, y] = await Promise.all([
-                            a.to_json(),
-                            b.to_json(),
+                            view0.to_json(),
+                            view1.to_json(),
                         ]);
+
                         if (JSON.stringify(x) === JSON.stringify(y)) {
-                            return;
+                            resolve();
                         }
+                    });
+
+                    await action();
+                    await Promise.race([
+                        promise,
+                        new Promise((resolve) => setTimeout(resolve, 2000)),
+                    ]);
 
-                        await new Promise((resolve) =>
-                            setTimeout(resolve, 100),
-                        );
-                    }
+                    await view1.remove_update(token);
                 };
 
                 const worker0 = await perspective.worker();
@@ -146,12 +152,13 @@ import perspective from "./perspective_client";
                 const view0 = await table0.view();
                 const table1 = await worker1.table(view0);
                 const view1 = await table1.view();
-                await table0.replace([
-                    { x: 5, y: 6 },
-                    { x: 7, y: 8 },
-                ]);
+                await sync(view0, view1, () =>
+                    table0.replace([
+                        { x: 5, y: 6 },
+                        { x: 7, y: 8 },
+                    ]),
+                );
 
-                await settle(view0, view1);
                 return [await view0.to_json(), await view1.to_json()];
             });
 
@@ -178,20 +185,26 @@ import perspective from "./perspective_client";
                     ),
                 );
 
-                const settle = async (a, b) => {
-                    for (let i = 0; i < 50; i++) {
+                const sync = async (view0, view1, action) => {
+                    const { promise, resolve } = Promise.withResolvers();
+                    const token = await view1.on_update(async () => {
                         const [x, y] = await Promise.all([
-                            a.to_json(),
-                            b.to_json(),
+                            view0.to_json(),
+                            view1.to_json(),
                         ]);
+
                         if (JSON.stringify(x) === JSON.stringify(y)) {
-                            return;
+                            resolve();
                         }
+                    });
+
+                    await action();
+                    await Promise.race([
+                        promise,
+                        new Promise((resolve) => setTimeout(resolve, 2000)),
+                    ]);
 
-                        await new Promise((resolve) =>
-                            setTimeout(resolve, 100),
-                        );
-                    }
+                    await view1.remove_update(token);
                 };
 
                 const worker0 = await perspective.worker();
@@ -200,8 +213,7 @@ import perspective from "./perspective_client";
                 const view0 = await table0.view();
                 const table1 = await worker1.table(view0);
                 const view1 = await table1.view();
-                await table0.clear();
-                await settle(view0, view1);
+                await sync(view0, view1, () => table0.clear());
                 return [await view0.to_json(), await view1.to_json()];
             });
 
@@ -224,20 +236,26 @@ import perspective from "./perspective_client";
                     ),
                 );
 
-                const settle = async (a, b) => {
-                    for (let i = 0; i < 50; i++) {
+                const sync = async (view0, view1, action) => {
+                    const { promise, resolve } = Promise.withResolvers();
+                    const token = await view1.on_update(async () => {
                         const [x, y] = await Promise.all([
-                            a.to_json(),
-                            b.to_json(),
+                            view0.to_json(),
+                            view1.to_json(),
                         ]);
+
                         if (JSON.stringify(x) === JSON.stringify(y)) {
-                            return;
+                            resolve();
                         }
+                    });
 
-                        await new Promise((resolve) =>
-                            setTimeout(resolve, 100),
-                        );
-                    }
+                    await action();
+                    await Promise.race([
+                        promise,
+                        new Promise((resolve) => setTimeout(resolve, 2000)),
+                    ]);
+
+                    await view1.remove_update(token);
                 };
 
                 const worker0 = await perspective.worker();
@@ -249,8 +267,10 @@ import perspective from "./perspective_client";
                 const view0 = await table0.view({ columns: ["y"] });
                 const table1 = await worker1.table(view0);
                 const view1 = await table1.view();
-                await table0.replace([{ x: 1, y: 20 }]);
-                await settle(view0, view1);
+                await sync(view0, view1, () =>
+                    table0.replace([{ x: 1, y: 20 }]),
+                );
+
                 return [await view0.to_json(), await view1.to_json()];
             });
 
@@ -273,20 +293,26 @@ import perspective from "./perspective_client";
                     ),
                 );
 
-                const settle = async (a, b) => {
-                    for (let i = 0; i < 50; i++) {
+                const sync = async (view0, view1, action) => {
+                    const { promise, resolve } = Promise.withResolvers();
+                    const token = await view1.on_update(async () => {
                         const [x, y] = await Promise.all([
-                            a.to_json(),
-                            b.to_json(),
+                            view0.to_json(),
+                            view1.to_json(),
                         ]);
+
                         if (JSON.stringify(x) === JSON.stringify(y)) {
-                            return;
+                            resolve();
                         }
+                    });
+
+                    await action();
+                    await Promise.race([
+                        promise,
+                        new Promise((resolve) => setTimeout(resolve, 2000)),
+                    ]);
 
-                        await new Promise((resolve) =>
-                            setTimeout(resolve, 100),
-                        );
-                    }
+                    await view1.remove_update(token);
                 };
 
                 const worker0 = await perspective.worker();
@@ -298,15 +324,15 @@ import perspective from "./perspective_client";
                 const view0 = await table0.view();
                 const table1 = await worker1.table(view0);
                 const view1 = await table1.view();
-                await table0.replace([
-                    { x: 3, y: 40 },
-                    { x: 5, y: 6 },
-                ]);
+                await sync(view0, view1, () =>
+                    table0.replace([
+                        { x: 3, y: 40 },
+                        { x: 5, y: 6 },
+                    ]),
+                );
 
-                await settle(view0, view1);
                 const replaced = [await view0.to_json(), await view1.to_json()];
-                await table0.clear();
-                await settle(view0, view1);
+                await sync(view0, view1, () => table0.clear());
                 return [
                     replaced,
                     [await view0.to_json(), await view1.to_json()],
diff --git a/rust/perspective-js/test/js/registry.spec.js b/rust/perspective-js/test/js/registry.spec.js
index b938a1acb2..26abc2a560 100644
--- a/rust/perspective-js/test/js/registry.spec.js
+++ b/rust/perspective-js/test/js/registry.spec.js
@@ -22,7 +22,7 @@ const URLS = {
     cdn: `${CLIENT}/dist/cdn/perspective.js`,
     viewer_cdn: `${VIEWER}/dist/cdn/perspective-viewer.js`,
     client_wasm: `${CLIENT}/dist/wasm/perspective-js.wasm`,
-    migrate_wasm: `${CLIENT}/dist/wasm/perspective-migrate-js.wasm`,
+    migrate_wasm: `${CLIENT}/dist/wasm/perspective-migrate.wasm`,
     wasm32: `${SERVER}/dist/wasm/perspective-server.wasm`,
     wasm64: `${SERVER}/dist/wasm/perspective-server.memory64.wasm`,
 };
diff --git a/rust/perspective-migrate-js/Cargo.toml b/rust/perspective-migrate-js/Cargo.toml
deleted file mode 100644
index 83bd0ca42d..0000000000
--- a/rust/perspective-migrate-js/Cargo.toml
+++ /dev/null
@@ -1,33 +0,0 @@
-#  ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
-#  ┃ ██████ ██████ ██████       █      █      █      █      █ █▄  ▀███ █       ┃
-#  ┃ ▄▄▄▄▄█ █▄▄▄▄▄ ▄▄▄▄▄█  ▀▀▀▀▀█▀▀▀▀▀ █ ▀▀▀▀▀█ ████████▌▐███ ███▄  ▀█ █ ▀▀▀▀▀ ┃
-#  ┃ █▀▀▀▀▀ █▀▀▀▀▀ █▀██▀▀ ▄▄▄▄▄ █ ▄▄▄▄▄█ ▄▄▄▄▄█ ████████▌▐███ █████▄   █ ▄▄▄▄▄ ┃
-#  ┃ █      ██████ █  ▀█▄       █ ██████      █      ███▌▐███ ███████▄ █       ┃
-#  ┣━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┫
-#  ┃ Copyright (c) 2017, the Perspective Authors.                              ┃
-#  ┃ ╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌ ┃
-#  ┃ This file is part of the Perspective library, distributed under the terms ┃
-#  ┃ of the [Apache License 2.0](https://www.apache.org/licenses/LICENSE-2.0). ┃
-#  ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
-
-[package]
-name = "perspective-migrate-js"
-version = "5.6.1"
-authors = ["Andrew Stein <steinlink@gmail.com>"]
-edition = "2024"
-description = "WebAssembly bindings for `perspective-migrate`, shipped with `@perspective-dev/client`."
-repository = "https://github.com/perspective-dev/perspective"
-license = "Apache-2.0"
-homepage = "https://perspective-dev.github.io"
-publish = false
-
-[lib]
-crate-type = ["cdylib", "rlib"]
-path = "src/lib.rs"
-
-[dependencies]
-perspective-migrate = { version = "5.6.1" }
-serde = { version = "1.0", features = ["derive"] }
-serde_json = { version = "1.0.107", features = ["preserve_order"] }
-serde-wasm-bindgen = "0.6.0"
-wasm-bindgen = { version = "=0.2.108" }
diff --git a/rust/perspective-migrate-js/src/lib.rs b/rust/perspective-migrate-js/src/lib.rs
deleted file mode 100644
index 3e8b063640..0000000000
--- a/rust/perspective-migrate-js/src/lib.rs
+++ /dev/null
@@ -1,41 +0,0 @@
-// ┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
-// ┃ ██████ ██████ ██████       █      █      █      █      █ █▄  ▀███ █       ┃
-// ┃ ▄▄▄▄▄█ █▄▄▄▄▄ ▄▄▄▄▄█  ▀▀▀▀▀█▀▀▀▀▀ █ ▀▀▀▀▀█ ████████▌▐███ ███▄  ▀█ █ ▀▀▀▀▀ ┃
-// ┃ █▀▀▀▀▀ █▀▀▀▀▀ █▀██▀▀ ▄▄▄▄▄ █ ▄▄▄▄▄█ ▄▄▄▄▄█ ████████▌▐███ █████▄   █ ▄▄▄▄▄ ┃
-// ┃ █      ██████ █  ▀█▄       █ ██████      █      ███▌▐███ ███████▄ █       ┃
-// ┣━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┫
-// ┃ Copyright (c) 2017, the Perspective Authors.                              ┃
-// ┃ ╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌╌ ┃
-// ┃ This file is part of the Perspective library, distributed under the terms ┃
-// ┃ of the [Apache License 2.0](https://www.apache.org/licenses/LICENSE-2.0). ┃
-// ┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛
-
-use perspective_migrate::{Kind, Migrator};
-use serde::Serialize;
-use wasm_bindgen::prelude::*;
-
-/// Upgrade a persisted Perspective config to the current schema, returning
-/// `{value, notices, steps}`.
-#[wasm_bindgen]
-pub fn migrate(kind: &str, from: Option<String>, value: JsValue) -> Result<JsValue, JsError> {
-    let kind = match kind {
-        "view" => Kind::View,
-        "viewer" => Kind::Viewer,
-        "workspace" => Kind::Workspace,
-        _ => {
-            return Err(JsError::new(&format!(
-                "Unknown config kind `{kind}`; expected `view`, `viewer` or `workspace`"
-            )));
-        },
-    };
-
-    let value: serde_json::Value = serde_wasm_bindgen::from_value(value)?;
-    let migrated = Migrator::new().migrate(kind, from.as_deref(), value)?;
-    let result = serde_json::json!({
-        "value": migrated.value,
-        "notices": migrated.notices,
-        "steps": migrated.steps,
-    });
-
-    Ok(result.serialize(&serde_wasm_bindgen::Serializer::json_compatible())?)
-}
diff --git a/rust/perspective-migrate/Cargo.toml b/rust/perspective-migrate/Cargo.toml
index f49c44cdce..fa3d7df0f6 100644
--- a/rust/perspective-migrate/Cargo.toml
+++ b/rust/perspective-migrate/Cargo.toml
@@ -25,11 +25,14 @@ documentation = "https://docs.rs/perspective-migrate"
 include = ["src/**/*", "Cargo.toml"]
 
 [lib]
+crate-type = ["cdylib", "rlib"]
 path = "src/lib.rs"
 
 [dependencies]
 serde = { version = "1.0", features = ["derive"] }
 serde_json = { version = "1.0.107", features = ["preserve_order"] }
+serde-wasm-bindgen = "0.6.0"
+wasm-bindgen = { version = "=0.2.108" }
 
 [dev-dependencies]
 perspective-client = { path = "../perspective-client" }
diff --git a/rust/perspective-migrate/src/lib.rs b/rust/perspective-migrate/src/lib.rs
index b178f580b0..a3c2838f0d 100644
--- a/rust/perspective-migrate/src/lib.rs
+++ b/rust/perspective-migrate/src/lib.rs
@@ -268,3 +268,31 @@ fn stamp(kind: Kind, version: &str, value: &mut Value) {
         },
     }
 }
+
+use wasm_bindgen::prelude::*;
+
+/// Upgrade a persisted Perspective config to the current schema, returning
+/// `{value, notices, steps}`.
+#[wasm_bindgen]
+pub fn migrate(kind: &str, from: Option<String>, value: JsValue) -> Result<JsValue, JsError> {
+    let kind = match kind {
+        "view" => Kind::View,
+        "viewer" => Kind::Viewer,
+        "workspace" => Kind::Workspace,
+        _ => {
+            return Err(JsError::new(&format!(
+                "Unknown config kind `{kind}`; expected `view`, `viewer` or `workspace`"
+            )));
+        },
+    };
+
+    let value: serde_json::Value = serde_wasm_bindgen::from_value(value)?;
+    let migrated = Migrator::new().migrate(kind, from.as_deref(), value)?;
+    let result = serde_json::json!({
+        "value": migrated.value,
+        "notices": migrated.notices,
+        "steps": migrated.steps,
+    });
+
+    Ok(result.serialize(&serde_wasm_bindgen::Serializer::json_compatible())?)
+}
diff --git a/rust/perspective-viewer/src/ts/bootstrap.ts b/rust/perspective-viewer/src/ts/bootstrap.ts
index 2037aad5c2..43aa9fc1e4 100644
--- a/rust/perspective-viewer/src/ts/bootstrap.ts
+++ b/rust/perspective-viewer/src/ts/bootstrap.ts
@@ -109,7 +109,7 @@ function is_registration(
  * ```javascript
  * await init_client({
  *     viewer: () => fetch("perspective-viewer.wasm"),
- *     migrate: () => fetch("perspective-migrate-js.wasm"),
+ *     migrate: () => fetch("perspective-migrate.wasm"),
  * });
  * ```
  */
diff --git a/rust/perspective-viewer/src/ts/perspective-viewer.cdn.ts b/rust/perspective-viewer/src/ts/perspective-viewer.cdn.ts
index 3c96e1e282..a98b7ecf03 100644
--- a/rust/perspective-viewer/src/ts/perspective-viewer.cdn.ts
+++ b/rust/perspective-viewer/src/ts/perspective-viewer.cdn.ts
@@ -27,7 +27,7 @@ register_default({
                 import.meta.url,
                 "viewer",
                 "client",
-                "perspective-migrate-js.wasm",
+                "perspective-migrate.wasm",
             ),
         ),
 });
diff --git a/rust/perspective-viewer/test/js/multi_panel/restore_workspace_layout.spec.ts b/rust/perspective-viewer/test/js/multi_panel/restore_workspace_layout.spec.ts
index 6484ca91d7..f5970176a2 100644
--- a/rust/perspective-viewer/test/js/multi_panel/restore_workspace_layout.spec.ts
+++ b/rust/perspective-viewer/test/js/multi_panel/restore_workspace_layout.spec.ts
@@ -145,7 +145,11 @@ test.describe("restoreWorkspace layout validation", () => {
     });
 
     test("drops an existing panel the layout omits", async ({ page }) => {
-        const layout = split("horizontal", [0.5, 0.5], [tab("one"), tab("two")]);
+        const layout = split(
+            "horizontal",
+            [0.5, 0.5],
+            [tab("one"), tab("two")],
+        );
         const result = await try_restore(page, { layout });
         expect(result.error).toBeNull();
         expect(result.panels).toEqual(["one", "two"]);