refactor: unify tool-starting logic with shared useStartTool hook

- New useStartTool hook: calls working createInstance+startInstance API
- WorkspacesPage: uses shared hook instead of inline createInstance logic
- WorkspaceDetailPage ToolsTab: uses shared hook instead of broken createWorkspaceInstance
- Both pages now use identical StartToolModal + identical start logic

Quality gates: tsc --noEmit clean

apps/web/src/pages/workspaces.tsx

@@ -4,10 +4,10 @@ import { useState } from "react";
 import { Icon } from "../components/icon";
 import { useWorkspaces } from "../hooks/use-workspaces";
 import { useWorkspaceActions } from "../hooks/use-workspace-actions";
+import { useStartTool } from "../hooks/use-start-tool";
 import { WorkspaceCard } from "../components/workspace-card";
 import { WorkspaceCreateForm } from "../components/workspace-create-form";
 import { StartToolModal } from "../components/start-tool-modal";
-import { createInstance, startInstance } from "../api/sessions";
 import type { Workspace } from "../types/workspace";
 
 export function WorkspacesPage() {
@@ -16,6 +16,7 @@ export function WorkspacesPage() {
 
 	const { workspaces, loading, error, refresh } = useWorkspaces();
 	const actions = useWorkspaceActions();
+	const { startTool } = useStartTool();
 
 	const handleDelete = async (workspace: Workspace) => {
 		await actions.delete(workspace, refresh);
@@ -35,29 +36,15 @@ export function WorkspacesPage() {
 		configProfileId?: string,
 	) => {
 		if (!startWorkspace) return;
-		try {
-			const instance = await createInstance(
-				startWorkspace.project_id,
-				startWorkspace.repo_id,
-				toolTypeId,
-				`${startWorkspace.name} - ${toolTypeId}`,
-				undefined,
-				undefined,
-				undefined,
-				configProfileId,
-				[],
-				startWorkspace.id,
-			);
-			await startInstance(
-				startWorkspace.project_id,
-				startWorkspace.repo_id,
-				instance.id,
-				configProfileId,
-			);
+		const instance = await startTool(
+			startWorkspace,
+			toolTypeId,
+			undefined,
+			configProfileId,
+		);
+		if (instance) {
 			setStartWorkspace(null);
 			await refresh();
-		} catch (err) {
-			alert(err instanceof Error ? err.message : "Failed to start tool");
 		}
 	};