Adopt workspace_integrate_upstream API in desktop app

- Add "Rebase onto target" stack context menu with dry-run preview modal
- Migrate IntegrateUpstreamModal from old Resolution API to BottomUpdate API
- Unapply fully-integrated stacks, rebase/merge the rest
- Backend: expose bottomSelector on StackStatus for building BottomUpdates

Author: mtsgrd

apps/desktop/src/components/stack/RebaseStackModal.svelte

@@ -0,0 +1,140 @@
+<script lang="ts" module>
+	export type RebaseStackModalProps = {
+		projectId: string;
+		stackId: string | undefined;
+	};
+</script>
+
+<script lang="ts">
+	import { parseQueryError } from "$lib/error/error";
+	import { STACK_SERVICE } from "$lib/stacks/stackService.svelte";
+	import { inject } from "@gitbutler/core/context";
+	import { Button, Modal } from "@gitbutler/ui";
+	import { tick } from "svelte";
+	import type { BottomUpdate, WorkspaceState } from "@gitbutler/but-sdk";
+
+	const { projectId, stackId }: RebaseStackModalProps = $props();
+
+	const stackService = inject(STACK_SERVICE);
+	const [integrateUpstream, integrateOp] = stackService.workspaceIntegrateUpstream;
+
+	let modal = $state<Modal>();
+	let dryRunResult = $state<WorkspaceState | undefined>();
+	let dryRunError = $state<string | undefined>();
+	let bottomUpdates = $state<BottomUpdate[]>([]);
+
+	export async function show() {
+		dryRunResult = undefined;
+		dryRunError = undefined;
+		bottomUpdates = [];
+
+		try {
+			const branches = await stackService.fetchBranches(projectId, stackId!);
+			if (!branches || branches.length === 0) {
+				dryRunError = "No branches found in this stack.";
+				await tick();
+				modal?.show();
+				return;
+			}
+
+			// The bottom branch is the last in the array (ordered top to bottom).
+			// Its bottom-most commit is the last in its commits array.
+			const bottomBranch = branches[branches.length - 1]!;
+			const bottomCommit = bottomBranch.commits[bottomBranch.commits.length - 1];
+
+			if (bottomCommit) {
+				bottomUpdates = [
+					{
+						kind: "rebase",
+						selector: { type: "commit", subject: bottomCommit.id },
+					},
+				];
+			} else {
+				// Empty branch — use the branch reference as selector
+				bottomUpdates = [
+					{
+						kind: "rebase",
+						selector: {
+							type: "reference",
+							subject: bottomBranch.reference,
+						},
+					},
+				];
+			}
+
+			const result = await integrateUpstream({
+				projectId,
+				updates: bottomUpdates,
+				dryRun: true,
+			});
+
+			dryRunResult = result;
+		} catch (err: unknown) {
+			dryRunError = parseQueryError(err).message;
+		}
+
+		await tick();
+		modal?.show();
+	}
+
+	const replacedCount = $derived(
+		dryRunResult ? Object.keys(dryRunResult.replacedCommits).length : 0,
+	);
+</script>
+
+<Modal
+	bind:this={modal}
+	width="small"
+	title="Rebase stack"
+	onSubmit={async (close) => {
+		await integrateUpstream({
+			projectId,
+			updates: bottomUpdates,
+			dryRun: false,
+		});
+		close();
+	}}
+>
+	{#if dryRunError}
+		<p class="text-13 text-body">Failed to preview rebase:</p>
+		<p class="text-13 text-body text-error" style="user-select: text">{dryRunError}</p>
+	{:else if dryRunResult}
+		<p class="text-13 text-body">This will rebase your stack onto the latest target branch.</p>
+		{#if replacedCount > 0}
+			<p class="text-13 text-body details">
+				{replacedCount}
+				{replacedCount === 1 ? "commit" : "commits"} will be rewritten.
+			</p>
+		{:else}
+			<p class="text-13 text-body details">
+				Your stack is already up to date. No commits will be rewritten.
+			</p>
+		{/if}
+	{:else}
+		<p class="text-13 text-body">Loading preview...</p>
+	{/if}
+
+	{#snippet controls(close)}
+		<Button kind="outline" onclick={close}>Cancel</Button>
+		<Button
+			style="pop"
+			type="submit"
+			disabled={!!dryRunError || !dryRunResult}
+			loading={integrateOp.current.isLoading}
+		>
+			Rebase
+		</Button>
+	{/snippet}
+</Modal>
+
+<style lang="postcss">
+	.details {
+		margin-top: 8px;
+		color: var(--text-2);
+	}
+
+	.text-error {
+		color: var(--text-error);
+		word-break: break-word;
+	}
+</style>

apps/desktop/src/components/stack/StackDragHandle.svelte

@@ -1,10 +1,12 @@
 <script lang="ts">
 	import CollapseStackButton from "$components/branch/CollapseStackButton.svelte";
+	import RebaseStackModal from "$components/stack/RebaseStackModal.svelte";
 	import { IRC_SESSION_BRIDGE } from "$lib/irc/sessionBridge.svelte";
 	import { SETTINGS_SERVICE } from "$lib/settings/appSettings";
 	import { STACK_SERVICE } from "$lib/stacks/stackService.svelte";
 	import { inject } from "@gitbutler/core/context";
 	import { ContextMenuItem, ContextMenuSection, Icon, KebabButton } from "@gitbutler/ui";
+
 	import type { Stack } from "$lib/stacks/stack";
 
 	type Props = {
@@ -28,6 +30,8 @@
 	);
 	const isManuallyBridged = $derived(ircSessionBridge.isManuallyBridged(stackId));
 
+	let rebaseModal = $state<RebaseStackModal>();
+
 	function toggleBridging() {
 		if (!stackId) return;
 		ircSessionBridge.setManualBridge(stackId, !isManuallyBridged.current);
@@ -128,6 +132,15 @@
 				/>
 			</ContextMenuSection>
 			<ContextMenuSection>
+				<ContextMenuItem
+					label="Rebase onto target"
+					icon="refresh"
+					disabled={!stackId}
+					onclick={() => {
+						close();
+						rebaseModal?.show();
+					}}
+				/>
 				<ContextMenuItem
 					label="Unapply stack"
 					icon="eject"
@@ -153,6 +166,10 @@
 	</KebabButton>
 </div>
 
+{#if stackId}
+	<RebaseStackModal bind:this={rebaseModal} {projectId} {stackId} />
+{/if}
+
 <style lang="postcss">
 	.drag-handle-row {
 		display: flex;