Add "Start Coding Agent session" context menu item to branch headers

apps/desktop/src/components/BranchHeaderContextMenu.svelte

@@ -8,6 +8,7 @@
 </script>
 
 <script lang="ts">
+	import { goto } from '$app/navigation';
 	import BranchRenameModal, {
 		type BranchRenameModalProps
 	} from '$components/BranchRenameModal.svelte';
@@ -20,6 +21,7 @@
 	import { CLIPBOARD_SERVICE } from '$lib/backend/clipboard';
 	import { projectAiGenEnabled } from '$lib/config/config';
 	import { DEFAULT_FORGE_FACTORY } from '$lib/forge/forgeFactory.svelte';
+	import { codegenPath } from '$lib/routes/routes.svelte';
 	import { STACK_SERVICE } from '$lib/stacks/stackService.svelte';
 	import { URL_SERVICE } from '$lib/utils/url';
 	import { inject } from '@gitbutler/core/context';
@@ -99,6 +101,12 @@
 		aiConfigurationValid = await aiService.validateConfiguration();
 	}
 
+	async function startCodingSession() {
+		if (!stackId) return;
+		goto(`${codegenPath(projectId)}?stackId=${stackId}`);
+		close();
+	}
+
 	async function generateBranchName(stackId: string, branchName: string) {
 		if (!$aiGenEnabled || !aiConfigurationValid) return;
 
@@ -265,6 +273,17 @@
 				{/if}
 			</ContextMenuSection>
 			<ContextMenuSection>
+				{#if $aiGenEnabled && aiConfigurationValid && stackId}
+					<ContextMenuItem
+						label="Start Coding Agent session"
+						icon="ai"
+						testId={TestId.BranchHeaderContextMenu_StartCodingSession}
+						disabled={isReadOnly}
+						onclick={() => {
+							startCodingSession();
+						}}
+					/>
+				{/if}
 				{#if $aiGenEnabled && aiConfigurationValid && !branch.remoteTrackingBranch && stackId}
 					<ContextMenuItem
 						label="Generate branch name"

apps/desktop/src/routes/[projectId]/codegen/+page.svelte

@@ -4,16 +4,47 @@
 	import CodegenPage from '$components/codegen/CodegenPage.svelte';
 	import { codegenEnabled } from '$lib/config/uiFeatureFlags';
 	import { workspacePath } from '$lib/routes/routes.svelte';
+	import { STACK_SERVICE } from '$lib/stacks/stackService.svelte';
+	import { UI_STATE } from '$lib/state/uiState.svelte';
+	import { inject } from '@gitbutler/core/context';
 
 	// TODO: Refactor so we don't need non-null assertion.
 	const projectId = $derived(page.params.projectId!);
 
+	const uiState = inject(UI_STATE);
+	const stackService = inject(STACK_SERVICE);
+	const projectState = $derived(uiState.project(projectId));
+
+	// Check for stackId in URL query parameters
+	const urlStackId = $derived(page.url.searchParams.get('stackId'));
+	const stacks = $derived(stackService.stacks(projectId));
+
 	// Redirect users when feature is disabled
 	$effect(() => {
 		if (!$codegenEnabled) {
 			goto(workspacePath(projectId));
 		}
 	});
+
+	// Handle stackId URL parameter to auto-select branch
+	$effect(() => {
+		if (urlStackId && stacks.current.data) {
+			// Find the stack with the matching ID
+			const targetStack = stacks.current.data.find((s) => s.id === urlStackId);
+			if (targetStack && targetStack.heads.length > 0) {
+				// Set the selected Claude session to the first head of this stack
+				projectState.selectedClaudeSession.set({
+					stackId: urlStackId,
+					head: targetStack.heads[0].name
+				});
+
+				// Remove the stackId parameter from the URL to keep it clean
+				const newUrl = new URL(page.url);
+				newUrl.searchParams.delete('stackId');
+				goto(newUrl.toString(), { replaceState: true });
+			}
+		}
+	});
 </script>
 
 {#if $codegenEnabled}

packages/ui/src/lib/utils/testIds.ts

@@ -10,6 +10,7 @@ export enum TestId {
 	BranchHeaderContextMenu_OpenInBrowser = 'branch-header-context-menu-open-in-browser',
 	BranchHeaderContextMenu_CopyBranchName = 'branch-header-context-menu-copy-branch-name',
 	BranchHeaderContextMenu_AddRemoveDescription = 'branch-header-context-menu-add-remove-description',
+	BranchHeaderContextMenu_StartCodingSession = 'branch-header-context-menu-start-coding-session',
 	BranchHeaderContextMenu_GenerateBranchName = 'branch-header-context-menu-generate-branch-name',
 	BranchHeaderContextMenu_Rename = 'branch-header-context-menu-rename',
 	BranchHeaderContextMenu_Delete = 'branch-header-context-menu-delete',