diff --git a/apps/server/src/services/llm/tools/attribute_tools.ts b/apps/server/src/services/llm/tools/attribute_tools.ts
index f17799f7b2..ffb9b24bee 100644
--- a/apps/server/src/services/llm/tools/attribute_tools.ts
+++ b/apps/server/src/services/llm/tools/attribute_tools.ts
@@ -64,7 +64,7 @@ export const attributeTools = defineTools({
             value: z.string().optional().describe("The attribute value (for relations, this must be a target noteId)")
         }),
         mutates: true,
-        execute: async ({ noteId, type, name, value = "" }) => {
+        execute: ({ noteId, type, name, value = "" }) => {
             const note = becca.getNote(noteId);
             if (!note) {
                 return { error: "Note not found" };
@@ -98,7 +98,7 @@ export const attributeTools = defineTools({
             attributeId: z.string().describe("The ID of the attribute to delete")
         }),
         mutates: true,
-        execute: async ({ noteId, attributeId }) => {
+        execute: ({ noteId, attributeId }) => {
             const attribute = becca.getAttribute(attributeId);
             if (!attribute) {
                 return { error: "Attribute not found" };
diff --git a/apps/server/src/services/llm/tools/note_tools.ts b/apps/server/src/services/llm/tools/note_tools.ts
index 3c2ece135d..1702eeab54 100644
--- a/apps/server/src/services/llm/tools/note_tools.ts
+++ b/apps/server/src/services/llm/tools/note_tools.ts
@@ -103,7 +103,7 @@ export const noteTools = defineTools({
             content: z.string().describe("The new content for the note (Markdown for text notes, plain text for code notes)")
         }),
         mutates: true,
-        execute: async ({ noteId, content }) => {
+        execute: ({ noteId, content }) => {
             const note = becca.getNote(noteId);
             if (!note) {
                 return { error: "Note not found" };
@@ -132,7 +132,7 @@ export const noteTools = defineTools({
             content: z.string().describe("The content to append (Markdown for text notes, plain text for code notes)")
         }),
         mutates: true,
-        execute: async ({ noteId, content }) => {
+        execute: ({ noteId, content }) => {
             const note = becca.getNote(noteId);
             if (!note) {
                 return { error: "Note not found" };
@@ -195,7 +195,7 @@ export const noteTools = defineTools({
             mime: z.string().optional().describe("MIME type, REQUIRED for code notes (e.g. 'application/javascript;env=backend', 'text/jsx'). Ignored for other types.")
         }),
         mutates: true,
-        execute: async ({ parentNoteId, title, content, type, mime }) => {
+        execute: ({ parentNoteId, title, content, type, mime }) => {
             if (type === "code" && !mime) {
                 return { error: "mime is required when creating code notes" };
             }
diff --git a/apps/server/src/services/llm/tools/tool_registry.ts b/apps/server/src/services/llm/tools/tool_registry.ts
index 0df416037b..b8a1b6995e 100644
--- a/apps/server/src/services/llm/tools/tool_registry.ts
+++ b/apps/server/src/services/llm/tools/tool_registry.ts
@@ -12,14 +12,36 @@ import { tool } from "ai";
 import type { z } from "zod";
 import type { ToolSet } from "ai";
 
-export interface ToolDefinition {
+import sql from "../../sql.js";
+
+/**
+ * Type constraint that rejects Promises at compile time.
+ * Works by requiring `then` to be void if present - Promises have `then: Function`.
+ */
+type NotAPromise<T> = T & { then?: void };
+
+interface MutatingToolDefinition {
     description: string;
     inputSchema: z.ZodType;
-    /** Whether this tool modifies data (needs CLS + transaction wrapping). */
-    mutates?: boolean;
-    execute: (args: any) => Promise<unknown>;
+    /** Marks this tool as modifying data (needs CLS + transaction wrapping). */
+    mutates: true;
+    /**
+     * Execute the tool synchronously. Must NOT be async because better-sqlite3
+     * transactions are synchronous and would commit before awaits complete.
+     */
+    execute: (args: any) => NotAPromise<object>;
 }
 
+interface ReadOnlyToolDefinition {
+    description: string;
+    inputSchema: z.ZodType;
+    mutates?: false;
+    /** Execute the tool. May be async for read-only operations. */
+    execute: (args: any) => unknown;
+}
+
+export type ToolDefinition = MutatingToolDefinition | ReadOnlyToolDefinition;
+
 /**
  * A named collection of tool definitions that can be iterated or converted
  * to an AI SDK ToolSet.
@@ -34,14 +56,20 @@ export class ToolRegistry implements Iterable<[string, ToolDefinition]> {
 
     /**
      * Convert to an AI SDK ToolSet for use with the LLM chat providers.
+     * Mutating tools are wrapped in a transaction for consistency with MCP.
+     * (CLS context is provided by the route handler.)
      */
     toToolSet(): ToolSet {
         const set: ToolSet = {};
         for (const [name, def] of this) {
+            const execute = def.mutates
+                ? (args: unknown) => sql.transactional(() => def.execute(args))
+                : def.execute;
+
             set[name] = tool({
                 description: def.description,
                 inputSchema: def.inputSchema,
-                execute: def.execute
+                execute
             });
         }
         return set;
@@ -53,9 +81,13 @@ export class ToolRegistry implements Iterable<[string, ToolDefinition]> {
  *
  * ```ts
  * export const noteTools = defineTools({
- *     search_notes: { description: "...", inputSchema: z.object({...}), execute: async (args) => {...} },
+ *     search_notes: { description: "...", inputSchema: z.object({...}), execute: (args) => {...} },
+ *     create_note: { description: "...", inputSchema: z.object({...}), mutates: true, execute: (args) => {...} },
  * });
  * ```
+ *
+ * Note: Mutating tools (mutates: true) MUST have synchronous execute functions
+ * because better-sqlite3 transactions are synchronous.
  */
 export function defineTools(tools: Record<string, ToolDefinition>): ToolRegistry {
     return new ToolRegistry(tools);
diff --git a/apps/server/src/services/mcp/mcp_server.ts b/apps/server/src/services/mcp/mcp_server.ts
index 67cc8af3fc..382b5025c7 100644
--- a/apps/server/src/services/mcp/mcp_server.ts
+++ b/apps/server/src/services/mcp/mcp_server.ts
@@ -24,11 +24,15 @@ function registerTool(server: McpServer, name: string, def: ToolDefinition) {
     server.registerTool(name, {
         description: def.description,
         inputSchema: def.inputSchema
-    }, async (args: any): Promise<CallToolResult> => {
-        const run = () => def.execute(args);
-        const result = def.mutates
-            ? await cls.init(() => sql.transactional(run))
-            : await run();
+    }, (args: any): CallToolResult => {
+        const result = cls.init(() => {
+            cls.set("componentId", "mcp");
+
+            return def.mutates
+                ? sql.transactional(() => def.execute(args))
+                : def.execute(args);
+        });
+
         return { content: [{ type: "text", text: JSON.stringify(result) }] };
     });
 }