diff --git a/tools/ui/src/lib/components/app/chat/ChatMessages/ChatMessage/ChatMessageToolCall/ChatMessageToolCallBlockDefault.svelte b/tools/ui/src/lib/components/app/chat/ChatMessages/ChatMessage/ChatMessageToolCall/ChatMessageToolCallBlockDefault.svelte
index 03f6c27ba3..4608232fa6 100644
--- a/tools/ui/src/lib/components/app/chat/ChatMessages/ChatMessage/ChatMessageToolCall/ChatMessageToolCallBlockDefault.svelte
+++ b/tools/ui/src/lib/components/app/chat/ChatMessages/ChatMessage/ChatMessageToolCall/ChatMessageToolCallBlockDefault.svelte
@@ -6,13 +6,14 @@
 	import ToolCallBlock from './ToolCallBlock.svelte';
 	import { Loader2 } from '@lucide/svelte';
 	import { MarkdownContent, SyntaxHighlightedCode } from '$lib/components/app';
-	import { getBuiltinToolUi, MAX_HEIGHT_CODE_BLOCK } from '$lib/constants';
+	import { MAX_HEIGHT_CODE_BLOCK } from '$lib/constants';
 	import { FileTypeText, ToolResultKind } from '$lib/enums';
 	import type { DatabaseMessageExtra } from '$lib/types';
 	import {
 		type AgenticSection,
 		classifyToolResult,
 		formatJsonPretty,
+		getBuiltinToolUi,
 		parseToolResultWithImages
 	} from '$lib/utils';
 
diff --git a/tools/ui/src/lib/components/app/chat/ChatMessages/ChatMessage/ChatMessageToolCall/ToolCallBlock.svelte b/tools/ui/src/lib/components/app/chat/ChatMessages/ChatMessage/ChatMessageToolCall/ToolCallBlock.svelte
index 7d8358571a..c43495b6c7 100644
--- a/tools/ui/src/lib/components/app/chat/ChatMessages/ChatMessage/ChatMessageToolCall/ToolCallBlock.svelte
+++ b/tools/ui/src/lib/components/app/chat/ChatMessages/ChatMessage/ChatMessageToolCall/ToolCallBlock.svelte
@@ -11,10 +11,10 @@
 
 	import { Loader2, Wrench } from '@lucide/svelte';
 	import { CollapsibleContentBlock } from '$lib/components/app';
-	import { getBuiltinToolUi, ICON_CLASS_DEFAULT, ICON_CLASS_SPIN } from '$lib/constants';
+	import { ICON_CLASS_DEFAULT, ICON_CLASS_SPIN } from '$lib/constants';
 	import { AgenticSectionType } from '$lib/enums';
 	import { mcpStore } from '$lib/stores/mcp.svelte';
-	import type { AgenticSection, BuiltinToolUiEntry } from '$lib/utils';
+	import { type AgenticSection, type BuiltinToolUiEntry, getBuiltinToolUi } from '$lib/utils';
 	import type { Component, Snippet } from 'svelte';
 
 	type ToolCallBlockMetaWithError = TMeta & { errorMessage?: string };
diff --git a/tools/ui/src/lib/components/app/settings/SettingsChat/SettingsChatToolsTab.svelte b/tools/ui/src/lib/components/app/settings/SettingsChat/SettingsChatToolsTab.svelte
index 4d3b69c41c..c4682f174c 100644
--- a/tools/ui/src/lib/components/app/settings/SettingsChat/SettingsChatToolsTab.svelte
+++ b/tools/ui/src/lib/components/app/settings/SettingsChat/SettingsChatToolsTab.svelte
@@ -3,11 +3,12 @@
 	import { McpServerIdentity, TruncatedText } from '$lib/components/app';
 	import { Checkbox } from '$lib/components/ui/checkbox';
 	import * as Collapsible from '$lib/components/ui/collapsible';
-	import { getBuiltinToolUi, ICON_CLASS_DEFAULT } from '$lib/constants';
+	import { ICON_CLASS_DEFAULT } from '$lib/constants';
 	import { ToolSource } from '$lib/enums/tools.enums';
 	import { mcpStore } from '$lib/stores/mcp.svelte';
 	import { permissionsStore } from '$lib/stores/permissions.svelte';
 	import { toolsStore } from '$lib/stores/tools.svelte';
+	import { getBuiltinToolUi } from '$lib/utils';
 	import { SvelteSet } from 'svelte/reactivity';
 
 	let expandedGroups = new SvelteSet<string>();
diff --git a/tools/ui/src/lib/constants/built-in-tools.constants.ts b/tools/ui/src/lib/constants/built-in-tools.constants.ts
index ec0826fbc3..70b7d895e6 100644
--- a/tools/ui/src/lib/constants/built-in-tools.constants.ts
+++ b/tools/ui/src/lib/constants/built-in-tools.constants.ts
@@ -48,9 +48,3 @@ export const BUILTIN_TOOL_UI: Readonly<Record<BuiltInTool, BuiltinToolUiEntry>>
 	},
 	[BuiltInTool.WRITE_FILE]: { icon: FilePlus, label: 'Write file', source: ToolSource.BUILTIN }
 } as const;
-
-export function getBuiltinToolUi(toolName: string | undefined): BuiltinToolUiEntry | null {
-	if (!toolName) return null;
-
-	return (BUILTIN_TOOL_UI as Record<string, BuiltinToolUiEntry>)[toolName] ?? null;
-}
diff --git a/tools/ui/src/lib/constants/control-actions.constants.ts b/tools/ui/src/lib/constants/control-actions.constants.ts
index 935ae9542a..c8ebf701b1 100644
--- a/tools/ui/src/lib/constants/control-actions.constants.ts
+++ b/tools/ui/src/lib/constants/control-actions.constants.ts
@@ -3,5 +3,3 @@
 export const CONTROL_ACTION = {
 	END_REASONING: 'reasoning_end'
 } as const;
-
-export type ControlAction = (typeof CONTROL_ACTION)[keyof typeof CONTROL_ACTION];
diff --git a/tools/ui/src/lib/constants/floating-ui-constraints.constants.ts b/tools/ui/src/lib/constants/floating-ui-constraints.constants.ts
deleted file mode 100644
index 003fc77acb..0000000000
--- a/tools/ui/src/lib/constants/floating-ui-constraints.constants.ts
+++ /dev/null
@@ -1,2 +0,0 @@
-export const VIEWPORT_GUTTER = 8;
-export const MENU_OFFSET = 6;
diff --git a/tools/ui/src/lib/constants/headers.constants.ts b/tools/ui/src/lib/constants/headers.constants.ts
new file mode 100644
index 0000000000..8e0ccb9745
--- /dev/null
+++ b/tools/ui/src/lib/constants/headers.constants.ts
@@ -0,0 +1,29 @@
+/** HTTP header handling for API and MCP requests. */
+export const HEADERS = {
+	/** Canonical casing for the Authorization header (RFC 7235) */
+	AUTHORIZATION: 'Authorization',
+	/** Bearer scheme prefix used for Authorization headers (RFC 6750) */
+	BEARER: 'Bearer ',
+	/** Content-Type HTTP header name */
+	CONTENT_TYPE: 'Content-Type',
+	/** Partial-redaction rules for MCP headers: header name -> visible trailing chars */
+	PARTIAL_REDACT: new Map<string, number>([['mcp-session-id', 5]]),
+
+	/** Header names whose values should be redacted in diagnostic logs */
+	REDACTED: new Set([
+		'authorization',
+		'api-key',
+		'cookie',
+		'mcp-session-id',
+		'proxy-authorization',
+		'set-cookie',
+		'x-auth-token',
+		'x-api-key'
+	]),
+
+	/** Header carrying the stream-session identity (conversation id, optionally with a model suffix) */
+	X_CONVERSATION_ID_HEADER: 'X-Conversation-Id',
+
+	/** Header carrying the working directory a tool call runs in; the model cannot override it */
+	X_TOOL_CWD_HEADER: 'x-tool-cwd'
+};
diff --git a/tools/ui/src/lib/constants/index.ts b/tools/ui/src/lib/constants/index.ts
index bae0e736e4..5d1260e036 100644
--- a/tools/ui/src/lib/constants/index.ts
+++ b/tools/ui/src/lib/constants/index.ts
@@ -18,14 +18,13 @@ export * from './content-detection.constants';
 export * from './built-in-tools.constants';
 export * from './cache.constants';
 export * from './chat-form.constants';
-export * from './chat-commands.constants';
 export * from './cli-flags.constants';
 export * from './code-block.constants';
 export * from './context-keys.constants';
 export * from './control-actions.constants';
 export * from './css-classes.constants';
-export * from './floating-ui-constraints.constants';
 export * from './formatters.constants';
+export * from './headers.constants';
 export * from './key-value-pairs.constants';
 export * from './latex-protection.constants';
 export * from './literal-html.constants';
@@ -45,7 +44,6 @@ export * from './path-display.constants';
 export * from './model-id.constants';
 export * from './model-loading.constants';
 export * from './precision.constants';
-export * from './processing-info.constants';
 export * from './pwa.constants';
 export * from './routes.constants';
 export * from './sandbox.constants';
@@ -56,10 +54,7 @@ export * from './stream.constants';
 export * from './supported-file-types.constants';
 export * from './table-html-restorer.constants';
 export * from './title-generation.constants';
-export * from './tools.constants';
-export * from './tooltip-config.constants';
 export * from './ui.constants';
 export * from './uri-template.constants';
 export * from './url.constants';
-export * from './viewport.constants';
 export * from './working-directory.constants';
diff --git a/tools/ui/src/lib/constants/mcp.constants.ts b/tools/ui/src/lib/constants/mcp.constants.ts
index 507f44d09a..11013d2cb1 100644
--- a/tools/ui/src/lib/constants/mcp.constants.ts
+++ b/tools/ui/src/lib/constants/mcp.constants.ts
@@ -59,31 +59,6 @@ export const CORS_PROXY = {
 	URL_PARAM: 'url'
 } as const;
 
-/** HTTP header handling for API and MCP requests. */
-export const HEADERS = {
-	/** Canonical casing for the Authorization header (RFC 7235) */
-	AUTHORIZATION: 'Authorization',
-	/** Bearer scheme prefix used for Authorization headers (RFC 6750) */
-	BEARER: 'Bearer ',
-	/** Content-Type HTTP header name */
-	CONTENT_TYPE: 'Content-Type',
-
-	/** Partial-redaction rules for MCP headers: header name -> visible trailing chars */
-	PARTIAL_REDACT: new Map<string, number>([['mcp-session-id', 5]]),
-
-	/** Header names whose values should be redacted in diagnostic logs */
-	REDACTED: new Set([
-		'authorization',
-		'api-key',
-		'cookie',
-		'mcp-session-id',
-		'proxy-authorization',
-		'set-cookie',
-		'x-auth-token',
-		'x-api-key'
-	])
-};
-
 /** Standard SSE endpoint path indicators */
 export const MCP_SSE = {
 	ENDPOINT: '/sse',
diff --git a/tools/ui/src/lib/constants/processing-info.constants.ts b/tools/ui/src/lib/constants/processing-info.constants.ts
deleted file mode 100644
index 2c3f7dc534..0000000000
--- a/tools/ui/src/lib/constants/processing-info.constants.ts
+++ /dev/null
@@ -1,8 +0,0 @@
-export const PROCESSING_INFO_TIMEOUT = 2000;
-
-/**
- * Statistics units labels
- */
-export const STATS_UNITS = {
-	TOKENS_PER_SECOND: 't/s'
-} as const;
diff --git a/tools/ui/src/lib/constants/sandbox.constants.ts b/tools/ui/src/lib/constants/sandbox.constants.ts
index 11e5fcf8fc..9846e471a9 100644
--- a/tools/ui/src/lib/constants/sandbox.constants.ts
+++ b/tools/ui/src/lib/constants/sandbox.constants.ts
@@ -1,5 +1,4 @@
-import { BuiltInTool, JsonSchemaType, ToolCallType } from '$lib/enums';
-import type { OpenAIToolDefinition } from '$lib/types';
+import { BuiltInTool } from '$lib/enums';
 
 export const SANDBOX_TOOL_NAME = BuiltInTool.RUN_JAVASCRIPT;
 
@@ -12,48 +11,3 @@ export const SANDBOX_OUTPUT_MAX_CHARS = 8192;
 export const SANDBOX_EMPTY_OUTPUT = '(no output)';
 
 export const SANDBOX_TRUNCATION_NOTICE = '[output truncated]';
-
-const NERDAMER_DESCRIPTION = `
-Symbolic/numeric math via \`nerdamer\`
-nerdamer(expr,subs?,opts?)/nerdamer.func(...)→Expression Format via .text(fmt?) (fmt: 'decimals'|'fractions'|'scientific') eval via .evaluate(subs?)
-nerdamer(expr,{x:2}) substitutes numeric via opts 'numer' or .evaluate()
-simplify/expand/factor(expr) div/gcd/lcm(...) coeffs/partfrac(expr,var)
-diff/integrate(expr,var) defint(expr,lo,hi,var?) sum/product(expr,var,lo,hi) limit(expr,var,pt)
-solve(expr,var) solveEquations([eq1,eq2],[var1,var2])
-polarform/rectform/arg/realpart/imagpart(z)
-set/get Var/Constant(name,val?) setFunction(name,[params],body)
-IMPORTANT:Identifier 'nerdamer' has already been declared, use it directly`;
-
-/**
- * Build the sandbox tool definition. When `includeSymbolicMath` is true,
- * the description includes nerdamer API documentation; otherwise it
- * describes a plain JavaScript sandbox.
- */
-export function buildSandboxToolDefinition(includeSymbolicMath: boolean): OpenAIToolDefinition {
-	return {
-		function: {
-			description: includeSymbolicMath
-				? `Execute JS in a sandboxed browser worker (no DOM/page access). Top-level await ok; console.log for intermediates; top-level return is captured as result.${NERDAMER_DESCRIPTION}`
-				: 'Execute JS in a sandboxed browser worker (no DOM/page access). Top-level await ok; console.log for intermediates; top-level return is captured as result.',
-			name: SANDBOX_TOOL_NAME,
-			parameters: {
-				properties: {
-					code: {
-						description: 'JavaScript source to execute',
-						type: JsonSchemaType.STRING
-					},
-					timeout_ms: {
-						description: `Execution timeout in milliseconds, default ${SANDBOX_TIMEOUT_MS_DEFAULT}, max ${SANDBOX_TIMEOUT_MS_MAX}`,
-						type: JsonSchemaType.NUMBER
-					}
-				},
-				required: ['code'],
-				type: JsonSchemaType.OBJECT
-			}
-		},
-		type: ToolCallType.FUNCTION
-	};
-}
-
-/** @deprecated Use {@link buildSandboxToolDefinition} instead. Kept for backward compatibility. */
-export const SANDBOX_TOOL_DEFINITION = buildSandboxToolDefinition(true);
diff --git a/tools/ui/src/lib/constants/stream.constants.ts b/tools/ui/src/lib/constants/stream.constants.ts
index ad04a1e74d..64f67243c2 100644
--- a/tools/ui/src/lib/constants/stream.constants.ts
+++ b/tools/ui/src/lib/constants/stream.constants.ts
@@ -2,6 +2,10 @@
 // while the tab was hidden. covers brief background pauses without thrashing live streams
 export const STREAM_VISIBILITY_KICK_MS = 3000;
 
+// separator joining a conversation id and its per-model stream identity
+// suffix (conv::model) used by the server side replay buffer
+export const CONVERSATION_ID_SEPARATOR = '::';
+
 /**
  * Server-sent events wire format, shared by the chat stream and the
  * /models/sse status feed (text/event-stream).
diff --git a/tools/ui/src/lib/constants/tools.constants.ts b/tools/ui/src/lib/constants/tools.constants.ts
deleted file mode 100644
index 65f4457c96..0000000000
--- a/tools/ui/src/lib/constants/tools.constants.ts
+++ /dev/null
@@ -1,16 +0,0 @@
-import { ToolSource } from '$lib/enums/tools.enums';
-
-/** HTTP header carrying the working directory a tool call runs in. The server resolves relative paths against it; the model cannot override it. */
-export const X_TOOL_CWD_HEADER = 'x-tool-cwd';
-
-export const TOOL_GROUP_LABELS = {
-	[ToolSource.BUILTIN]: 'Built-in',
-	[ToolSource.CUSTOM]: 'JSON Schema',
-	[ToolSource.FRONTEND]: 'Browser'
-} as const;
-
-export const TOOL_SERVER_LABELS = {
-	[ToolSource.BUILTIN]: 'Built-in Tools',
-	[ToolSource.CUSTOM]: 'Custom Tools',
-	[ToolSource.FRONTEND]: 'Browser Tools'
-} as const;
diff --git a/tools/ui/src/lib/constants/tooltip-config.constants.ts b/tools/ui/src/lib/constants/tooltip-config.constants.ts
deleted file mode 100644
index ad76ab3522..0000000000
--- a/tools/ui/src/lib/constants/tooltip-config.constants.ts
+++ /dev/null
@@ -1 +0,0 @@
-export const TOOLTIP_DELAY_DURATION = 500;
diff --git a/tools/ui/src/lib/constants/ui.constants.ts b/tools/ui/src/lib/constants/ui.constants.ts
index a50153852e..3374b6e008 100644
--- a/tools/ui/src/lib/constants/ui.constants.ts
+++ b/tools/ui/src/lib/constants/ui.constants.ts
@@ -1,11 +1,40 @@
 import { ROUTES } from './routes.constants';
 import { Package, Search, Settings, SquarePen } from '@lucide/svelte';
 import McpLogo from '$lib/components/app/mcp/McpLogo.svelte';
+import { ToolSource } from '$lib/enums/tools.enums';
 import type { DesktopIconStripItem } from '$lib/types';
 
 export const FORK_TREE_DEPTH_PADDING = 8;
 export const SYSTEM_MESSAGE_PLACEHOLDER = 'System message';
 
+export const TOOL_GROUP_LABELS = {
+	[ToolSource.BUILTIN]: 'Built-in',
+	[ToolSource.CUSTOM]: 'JSON Schema',
+	[ToolSource.FRONTEND]: 'Browser'
+} as const;
+
+export const TOOL_SERVER_LABELS = {
+	[ToolSource.BUILTIN]: 'Built-in Tools',
+	[ToolSource.CUSTOM]: 'Custom Tools',
+	[ToolSource.FRONTEND]: 'Browser Tools'
+} as const;
+
+export const TOOLTIP_DELAY_DURATION = 500;
+
+export const VIEWPORT_GUTTER = 8;
+export const MENU_OFFSET = 6;
+
+export const PROCESSING_INFO_TIMEOUT = 2000;
+
+/**
+ * Statistics units labels
+ */
+export const STATS_UNITS = {
+	TOKENS_PER_SECOND: 't/s'
+} as const;
+
+export const DEFAULT_MOBILE_BREAKPOINT = 768;
+
 /** Icon used for the model selector and the `/model` slash command. */
 export const MODEL_SELECTOR_ICON = Package;
 
diff --git a/tools/ui/src/lib/constants/viewport.constants.ts b/tools/ui/src/lib/constants/viewport.constants.ts
deleted file mode 100644
index 26e202cfea..0000000000
--- a/tools/ui/src/lib/constants/viewport.constants.ts
+++ /dev/null
@@ -1 +0,0 @@
-export const DEFAULT_MOBILE_BREAKPOINT = 768;
diff --git a/tools/ui/src/lib/hooks/use-chat-form-pickers.svelte.ts b/tools/ui/src/lib/hooks/use-chat-form-pickers.svelte.ts
index 712189746b..986cc46c72 100644
--- a/tools/ui/src/lib/hooks/use-chat-form-pickers.svelte.ts
+++ b/tools/ui/src/lib/hooks/use-chat-form-pickers.svelte.ts
@@ -1,6 +1,7 @@
-import { getChatCommands, PROMPT_TRIGGER_PREFIX } from '$lib/constants';
+import { PROMPT_TRIGGER_PREFIX } from '$lib/constants';
 import { ChatFormCommandAction, KeyboardKey } from '$lib/enums';
 import type { ChatFormCommand } from '$lib/types';
+import { getChatCommands } from '$lib/utils';
 import {
 	type CommandDismissSnapshot,
 	findCommandToken,
diff --git a/tools/ui/src/lib/services/chat.service.ts b/tools/ui/src/lib/services/chat.service.ts
index a3f0f77aee..bc2cd9c1e2 100644
--- a/tools/ui/src/lib/services/chat.service.ts
+++ b/tools/ui/src/lib/services/chat.service.ts
@@ -5,6 +5,7 @@ import {
 	API_SLOTS,
 	API_STREAM,
 	CONTROL_ACTION,
+	HEADERS,
 	LEGACY_AGENTIC_REGEX,
 	REASONING_EFFORT_TOKENS,
 	SETTINGS_KEYS,
@@ -361,7 +362,7 @@ export class ChatService {
 			// server side replay buffer and powers discoverActiveStream on tab reopen. with an explicit
 			// model the ::model suffix keeps the per model session distinct
 			if (stream && conversationId) {
-				headers['X-Conversation-Id'] = streamIdentity(conversationId, options.model);
+				headers[HEADERS.X_CONVERSATION_ID_HEADER] = streamIdentity(conversationId, options.model);
 				// persist the pending stream before the fetch: a reload during the model load or
 				// the prompt processing must still find its way back to the session once it exists
 				ChatService.saveStreamState(conversationId, 0, options.model ?? null);
diff --git a/tools/ui/src/lib/services/index.ts b/tools/ui/src/lib/services/index.ts
index 8704b1bd6c..328d3b4828 100644
--- a/tools/ui/src/lib/services/index.ts
+++ b/tools/ui/src/lib/services/index.ts
@@ -276,7 +276,7 @@ export { MCPService } from './mcp.service';
  * - **toolsStore**: Exposes the tool definition when the sandbox is enabled
  * - **agenticStore**: Dispatches ToolSource.FRONTEND calls here
  *
- * @see buildSandboxToolDefinition in constants/sandbox.ts - tool schema sent to the LLM
+ * @see buildSandboxToolDefinition in utils/sandbox-tool - tool schema sent to the LLM
  * @see agenticStore in stores/agentic.svelte.ts - tool dispatch
  */
 export { SandboxService } from './sandbox.service';
diff --git a/tools/ui/src/lib/services/tools.service.ts b/tools/ui/src/lib/services/tools.service.ts
index cd6b12cebe..d15b213c75 100644
--- a/tools/ui/src/lib/services/tools.service.ts
+++ b/tools/ui/src/lib/services/tools.service.ts
@@ -1,5 +1,5 @@
 import { base } from '$app/paths';
-import { API_TOOLS, X_TOOL_CWD_HEADER } from '$lib/constants';
+import { API_TOOLS, HEADERS } from '$lib/constants';
 import { ToolResponseField } from '$lib/enums';
 import type { ServerBuiltinToolInfo, ToolExecutionResult } from '$lib/types';
 import { apiFetch } from '$lib/utils';
@@ -31,7 +31,7 @@ export class ToolsService {
 	): Promise<ToolExecutionResult> {
 		const result = await apiFetch<Record<string, unknown>>(API_TOOLS.EXECUTE, {
 			body: JSON.stringify({ params, tool: toolName }),
-			headers: cwd ? { [X_TOOL_CWD_HEADER]: cwd } : undefined,
+			headers: cwd ? { [HEADERS.X_TOOL_CWD_HEADER]: cwd } : undefined,
 			method: 'POST',
 			signal
 		});
@@ -60,7 +60,7 @@ export class ToolsService {
 	): Promise<Record<string, unknown>> {
 		return apiFetch<Record<string, unknown>>(API_TOOLS.EXECUTE, {
 			body: JSON.stringify({ params, tool: toolName }),
-			headers: cwd ? { [X_TOOL_CWD_HEADER]: cwd } : undefined,
+			headers: cwd ? { [HEADERS.X_TOOL_CWD_HEADER]: cwd } : undefined,
 			method: 'POST',
 			signal
 		});
@@ -89,7 +89,7 @@ export class ToolsService {
 	): AsyncGenerator<ToolStreamEvent> {
 		const headers = getJsonHeaders();
 
-		if (cwd) headers[X_TOOL_CWD_HEADER] = cwd;
+		if (cwd) headers[HEADERS.X_TOOL_CWD_HEADER] = cwd;
 
 		const response = await fetch(`${base}${API_TOOLS.EXECUTE}`, {
 			body: JSON.stringify({ params, stream: true, tool: toolName }),
diff --git a/tools/ui/src/lib/stores/chat.svelte.ts b/tools/ui/src/lib/stores/chat.svelte.ts
index 0d069eb35e..3965c4cbb5 100644
--- a/tools/ui/src/lib/stores/chat.svelte.ts
+++ b/tools/ui/src/lib/stores/chat.svelte.ts
@@ -12,6 +12,7 @@
  */
 
 import {
+	CONVERSATION_ID_SEPARATOR,
 	HEADERS,
 	INACTIVE_CONVERSATION,
 	STREAM_RESUME_RETRY_MS,
@@ -413,7 +414,7 @@ class ChatStore {
 
 		// extract the model suffix, the resume calls in handleStreamResponse must reuse the model
 		// the session was tagged with, not the live dropdown
-		const sepIdx = id.indexOf('::');
+		const sepIdx = id.indexOf(CONVERSATION_ID_SEPARATOR);
 		const attachedModel: string | null = sepIdx === -1 ? null : id.slice(sepIdx + 2);
 
 		this.setChatStreaming(convId, existingContent, targetMessageId, attachedModel);
@@ -828,7 +829,7 @@ class ChatStore {
 		for (const s of sessions) {
 			if (s && !s.is_done && typeof s.conversation_id === 'string' && s.conversation_id) {
 				// strip the optional ::model suffix, the sidebar set is keyed by the bare conv id
-				const sepIdx = s.conversation_id.indexOf('::');
+				const sepIdx = s.conversation_id.indexOf(CONVERSATION_ID_SEPARATOR);
 				const bareId = sepIdx === -1 ? s.conversation_id : s.conversation_id.slice(0, sepIdx);
 
 				running.add(bareId);
diff --git a/tools/ui/src/lib/stores/tools.svelte.ts b/tools/ui/src/lib/stores/tools.svelte.ts
index b1a946391a..ab9ebdeb3e 100644
--- a/tools/ui/src/lib/stores/tools.svelte.ts
+++ b/tools/ui/src/lib/stores/tools.svelte.ts
@@ -1,5 +1,4 @@
 import {
-	buildSandboxToolDefinition,
 	DISABLED_TOOL_KEYS_LOCALSTORAGE_KEY,
 	HOME_TILDE,
 	TOOL_GROUP_LABELS,
@@ -17,6 +16,7 @@ import { ToolsService } from '$lib/services/tools.service';
 import { mcpStore } from '$lib/stores/mcp.svelte';
 import { config } from '$lib/stores/settings.svelte';
 import type { OpenAIToolDefinition, ToolEntry, ToolGroup } from '$lib/types';
+import { buildSandboxToolDefinition } from '$lib/utils';
 import { SvelteMap, SvelteSet } from 'svelte/reactivity';
 
 /** Stable selection identity for a tool, shared by the disabled set and the permission store */
diff --git a/tools/ui/src/lib/types/chat.d.ts b/tools/ui/src/lib/types/chat.d.ts
index a476fce81a..cb93e77951 100644
--- a/tools/ui/src/lib/types/chat.d.ts
+++ b/tools/ui/src/lib/types/chat.d.ts
@@ -215,6 +215,18 @@ export interface FileMentionEntry {
  * command whose backing capability is unavailable (e.g. `/prompt` when no
  * MCP server exposes prompts): visible but greyed out and not selectable.
  */
+export interface ChatCommandsOptions {
+	/** Gates `/model`. */
+	showModelSelector: boolean;
+	/** Gates `/prompt`. */
+	hasPrompts: () => boolean;
+	/** Gates `/cwd`. */
+	hasCwdTools: () => boolean;
+}
+
+/** Protocol-level verbs accepted by the realtime inference control endpoint. Mirrors `CONTROL_ACTION`. */
+export type ControlAction = 'reasoning_end';
+
 export interface ChatFormCommand {
 	name: string;
 	description: string;
diff --git a/tools/ui/src/lib/types/index.ts b/tools/ui/src/lib/types/index.ts
index 27d0b4224b..a7e755040c 100644
--- a/tools/ui/src/lib/types/index.ts
+++ b/tools/ui/src/lib/types/index.ts
@@ -56,7 +56,9 @@ export type {
 	AttachmentDisplayItemsOptions,
 	FileProcessingResult,
 	FileMentionEntry,
-	ChatFormCommand
+	ChatFormCommand,
+	ChatCommandsOptions,
+	ControlAction
 } from './chat.d';
 
 // Database types
diff --git a/tools/ui/src/lib/utils/built-in-tools.ts b/tools/ui/src/lib/utils/built-in-tools.ts
new file mode 100644
index 0000000000..73b5547900
--- /dev/null
+++ b/tools/ui/src/lib/utils/built-in-tools.ts
@@ -0,0 +1,13 @@
+import { BUILTIN_TOOL_UI } from '$lib/constants';
+import type { BuiltinToolUiEntry } from '$lib/types';
+
+/**
+ * Resolve the UI metadata (label + icon) for a built-in tool by its name.
+ * Falls back to null for unknown or non-built-in tools so callers can render
+ * a generic chrome instead.
+ */
+export function getBuiltinToolUi(toolName: string | undefined): BuiltinToolUiEntry | null {
+	if (!toolName) return null;
+
+	return (BUILTIN_TOOL_UI as Record<string, BuiltinToolUiEntry>)[toolName] ?? null;
+}
diff --git a/tools/ui/src/lib/constants/chat-commands.constants.ts b/tools/ui/src/lib/utils/chat-commands.ts
similarity index 71%
rename from tools/ui/src/lib/constants/chat-commands.constants.ts
rename to tools/ui/src/lib/utils/chat-commands.ts
index d10d7b1519..9345f0a48e 100644
--- a/tools/ui/src/lib/constants/chat-commands.constants.ts
+++ b/tools/ui/src/lib/utils/chat-commands.ts
@@ -1,23 +1,14 @@
 import { SET_WORKING_DIRECTORY_LABEL } from '$lib/constants';
 import { ChatFormCommandAction } from '$lib/enums';
-import type { ChatFormCommand } from '$lib/types';
-
-interface ChatCommandsOptions {
-	/** Gates `/model`. */
-	showModelSelector: boolean;
-	/** Gates `/prompt`. */
-	hasPrompts: () => boolean;
-	/** Gates `/cwd`. */
-	hasCwdTools: () => boolean;
-}
+import type { ChatCommandsOptions, ChatFormCommand } from '$lib/types';
 
 /**
  * The slash commands surfaced by the `/` command picker, in display order.
  *
  * Availability is supplied as predicates rather than store imports: this
- * module is re-exported through the `$lib/constants` barrel, and importing
+ * module is re-exported through the `$lib/utils` barrel, and importing
  * stores at module load would create a circular dependency (the stores
- * themselves import from `$lib/constants`).
+ * themselves import from `$lib/utils`).
  */
 export function getChatCommands(options: ChatCommandsOptions): ChatFormCommand[] {
 	return [
diff --git a/tools/ui/src/lib/utils/index.ts b/tools/ui/src/lib/utils/index.ts
index 25c7234bb5..54d555fa1c 100644
--- a/tools/ui/src/lib/utils/index.ts
+++ b/tools/ui/src/lib/utils/index.ts
@@ -317,9 +317,17 @@ export { tryParseToolResultObject } from './tool-call-meta';
 // Per-tool UI metadata (label + icon) used by the tool-call chrome.
 // Re-exported through $lib/utils so renderer components can read the
 // label without depending on $lib/constants directly.
-export { getBuiltinToolUi } from '$lib/constants';
+export { getBuiltinToolUi } from './built-in-tools';
 export type { BuiltinToolUiEntry } from '$lib/types';
 
+// Chat command picker
+
+export { getChatCommands } from './chat-commands';
+
+// Sandbox tool definition
+// SANDBOX_TOOL_DEFINITION is deprecated; kept for backward compatibility.
+export { buildSandboxToolDefinition, SANDBOX_TOOL_DEFINITION } from './sandbox-tool';
+
 // Cryptography utilities
 
 export { uuid } from './uuid';
diff --git a/tools/ui/src/lib/utils/sandbox-tool.ts b/tools/ui/src/lib/utils/sandbox-tool.ts
new file mode 100644
index 0000000000..bc057e409d
--- /dev/null
+++ b/tools/ui/src/lib/utils/sandbox-tool.ts
@@ -0,0 +1,52 @@
+import {
+	SANDBOX_TIMEOUT_MS_DEFAULT,
+	SANDBOX_TIMEOUT_MS_MAX,
+	SANDBOX_TOOL_NAME
+} from '$lib/constants';
+import { JsonSchemaType, ToolCallType } from '$lib/enums';
+import type { OpenAIToolDefinition } from '$lib/types';
+
+const NERDAMER_DESCRIPTION = `
+Symbolic/numeric math via \`nerdamer\`
+nerdamer(expr,subs?,opts?)/nerdamer.func(...)→Expression Format via .text(fmt?) (fmt: 'decimals'|'fractions'|'scientific') eval via .evaluate(subs?)
+nerdamer(expr,{x:2}) substitutes numeric via opts 'numer' or .evaluate()
+simplify/expand/factor(expr) div/gcd/lcm(...) coeffs/partfrac(expr,var)
+diff/integrate(expr,var) defint(expr,lo,hi,var?) sum/product(expr,var,lo,hi) limit(expr,var,pt)
+solve(expr,var) solveEquations([eq1,eq2],[var1,var2])
+polarform/rectform/arg/realpart/imagpart(z)
+set/get Var/Constant(name,val?) setFunction(name,[params],body)
+IMPORTANT:Identifier 'nerdamer' has already been declared, use it directly`;
+
+/**
+ * Build the sandbox tool definition. When `includeSymbolicMath` is true,
+ * the description includes nerdamer API documentation; otherwise it
+ * describes a plain JavaScript sandbox.
+ */
+export function buildSandboxToolDefinition(includeSymbolicMath: boolean): OpenAIToolDefinition {
+	return {
+		function: {
+			description: includeSymbolicMath
+				? `Execute JS in a sandboxed browser worker (no DOM/page access). Top-level await ok; console.log for intermediates; top-level return is captured as result.${NERDAMER_DESCRIPTION}`
+				: 'Execute JS in a sandboxed browser worker (no DOM/page access). Top-level await ok; console.log for intermediates; top-level return is captured as result.',
+			name: SANDBOX_TOOL_NAME,
+			parameters: {
+				properties: {
+					code: {
+						description: 'JavaScript source to execute',
+						type: JsonSchemaType.STRING
+					},
+					timeout_ms: {
+						description: `Execution timeout in milliseconds, default ${SANDBOX_TIMEOUT_MS_DEFAULT}, max ${SANDBOX_TIMEOUT_MS_MAX}`,
+						type: JsonSchemaType.NUMBER
+					}
+				},
+				required: ['code'],
+				type: JsonSchemaType.OBJECT
+			}
+		},
+		type: ToolCallType.FUNCTION
+	};
+}
+
+/** @deprecated Use {@link buildSandboxToolDefinition} instead. Kept for backward compatibility. */
+export const SANDBOX_TOOL_DEFINITION = buildSandboxToolDefinition(true);
diff --git a/tools/ui/src/lib/utils/stream-identity.ts b/tools/ui/src/lib/utils/stream-identity.ts
index 253786a7e3..bf0946fc09 100644
--- a/tools/ui/src/lib/utils/stream-identity.ts
+++ b/tools/ui/src/lib/utils/stream-identity.ts
@@ -1,3 +1,5 @@
+import { CONVERSATION_ID_SEPARATOR } from '$lib/constants';
+
 /**
  * Build the conversation identity used by the server side replay buffer.
  *
@@ -11,5 +13,5 @@ export function streamIdentity(conversationId: string, model?: string | null): s
 
 	if (!model) return conversationId;
 
-	return `${conversationId}::${model}`;
+	return `${conversationId}${CONVERSATION_ID_SEPARATOR}${model}`;
 }