Interface: FusionInstance<TContext>

Defined in: packages/core/src/core/initFusion.ts:68

The initialized Fusion instance.

Provides context-typed factory methods for tools, presenters, prompts, middleware, and registry. Every method automatically inherits the TContext defined in initFusion<TContext>().

Type Parameters

Type Parameter	Description
TContext	The application context type

Properties

serializer

readonly serializer: JsonSerializer;

Defined in: packages/core/src/core/initFusion.ts:291

AOT JSON serializer.

Compile Zod schemas into hyper-fast stringify functions at boot time. Used internally by Presenters; exposed here for advanced use cases.

Example

const stringify = f.serializer.compile(myZodSchema);
if (stringify) {
    return success(data, stringify); // 2-5x faster
}

Methods

action()

action(name): FluentToolBuilder<TContext>;

Defined in: packages/core/src/core/initFusion.ts:127

Create a neutral action tool (no defaults applied).

Parameters

Parameter	Type	Description
name	string	Tool name in domain.action format

Returns

FluentToolBuilder<TContext>

A type-chaining FluentToolBuilder

Example

const updateUser = f.action('users.update')
    .describe('Update user profile')
    .idempotent()
    .withString('id', 'User ID')
    .withOptionalString('name', 'New display name')
    .handle(async (input, ctx) => {
        return ctx.db.user.update({ where: { id: input.id }, data: input });
    });

---

error()

error(code, message): ErrorBuilder;

Defined in: packages/core/src/core/initFusion.ts:234

Create a fluent, self-healing error builder.

Parameters

Parameter	Type	Description
code	ErrorCode	Canonical error code
message	string	Human-readable error message

Returns

ErrorBuilder

A chaining ErrorBuilder

Example

return f.error('NOT_FOUND', `Project "${id}" not found`)
    .suggest('Check the list for valid IDs')
    .actions('projects.list');

---

fsm()

fsm(config): StateMachineGate;

Defined in: packages/core/src/core/initFusion.ts:318

Create a Finite State Machine gate for temporal anti-hallucination.

Tools bound to FSM states (via .bindState()) are dynamically filtered from tools/list based on the current workflow state.

Parameters

Parameter	Type	Description
config	FsmConfig	FSM definition (states, transitions, initial state)

Returns

StateMachineGate

A new StateMachineGate instance

Example

const gate = f.fsm({
    id: 'checkout',
    initial: 'empty',
    states: {
        empty:     { on: { ADD_ITEM: 'has_items' } },
        has_items: { on: { CHECKOUT: 'payment' } },
        payment:   { on: { PAY: 'confirmed' } },
        confirmed: { type: 'final' },
    },
});

---

middleware()

middleware<TDerived>(derive): MiddlewareDefinition<TContext, TDerived>;

Defined in: packages/core/src/core/initFusion.ts:180

Define a context-derivation middleware.

Type Parameters

Type Parameter
TDerived extends Record<string, unknown>

Parameters

Parameter	Type
derive	(ctx) => TDerived | Promise<TDerived>

Returns

MiddlewareDefinition<TContext, TDerived>

Example

const withUser = f.middleware(async (ctx) => ({
  user: await ctx.db.users.findUnique(ctx.userId),
}));

---

mutation()

mutation(name): FluentToolBuilder<TContext>;

Defined in: packages/core/src/core/initFusion.ts:107

Create a destructive mutation tool (destructive: true by default).

Parameters

Parameter	Type	Description
name	string	Tool name in domain.action format

Returns

FluentToolBuilder<TContext>

A type-chaining FluentToolBuilder

Example

const deleteUser = f.mutation('users.delete')
    .describe('Delete a user permanently')
    .withString('id', 'User ID to delete')
    .handle(async (input, ctx) => {
        await ctx.db.user.delete({ where: { id: input.id } });
    });

---

presenter()

presenter<TSchema>(config): Presenter<TSchema["_output"]>;

Defined in: packages/core/src/core/initFusion.ts:144

Define a Presenter with the standard object-config API.

Type Parameters

Type Parameter
TSchema extends ZodType<any, any, any>

Parameters

Parameter	Type
config	Omit<PresenterConfig<TSchema["_output"]>, "schema"> & { schema: TSchema; }

Returns

Presenter<TSchema["_output"]>

Example

const InvoicePresenter = f.presenter({
  name: 'Invoice',
  schema: invoiceSchema,
  rules: ['CRITICAL: amount_cents is in CENTS.'],
  ui: (inv) => [ui.echarts({ ... })],
});

---

prompt()

Call Signature

prompt(name): FluentPromptBuilder<TContext>;

Defined in: packages/core/src/core/initFusion.ts:163

Define a prompt — fluent builder.

Parameters

Parameter	Type
name	string

Returns

FluentPromptBuilder<TContext>

Example

const greet = f.prompt('greet')
    .describe('Greet a user')
    .withString('name', 'User name')
    .handler(async (ctx, { name }) => ({
        messages: [PromptMessage.user(`Hello ${name}!`)],
    }));

Call Signature

prompt(name, config): PromptBuilder<TContext>;

Defined in: packages/core/src/core/initFusion.ts:164

Parameters

Parameter	Type
name	string
config	Omit<PromptConfig<TContext, Record<string, unknown>>, "handler"> & { handler: (ctx, args) => Promise<PromptResult>; }

Returns

PromptBuilder<TContext>

---

query()

query(name): FluentToolBuilder<TContext>;

Defined in: packages/core/src/core/initFusion.ts:89

Create a read-only query tool (readOnly: true by default).

Parameters

Parameter	Type	Description
name	string	Tool name in domain.action format

Returns

FluentToolBuilder<TContext>

A type-chaining FluentToolBuilder

Example

const listUsers = f.query('users.list')
    .describe('List users from the database')
    .withNumber('limit', 'Max results to return')
    .withOptionalEnum('status', ['active', 'inactive'], 'Filter by status')
    .handle(async (input, ctx) => {
        return ctx.db.user.findMany({ take: input.limit });
    });

---

registry()

registry(): ToolRegistry<TContext>;

Defined in: packages/core/src/core/initFusion.ts:195

Create a pre-typed ToolRegistry ready for registration.

Returns

ToolRegistry<TContext>

Example

const registry = f.registry();
registry.register(listUsers);

---

router()

router(prefix): FluentRouter<TContext>;

Defined in: packages/core/src/core/initFusion.ts:216

Create a router that shares prefix, middleware, and tags.

Parameters

Parameter	Type	Description
prefix	string	Common prefix for all tools (e.g. 'users')

Returns

FluentRouter<TContext>

A FluentRouter for creating child tools

Example

const users = f.router('users')
    .describe('User management')
    .use(requireAuth);

const listUsers = users.query('list')
    .withNumber('limit', 'Max results')
    .handle(async (input) => { ... });

---

sandbox()

sandbox(config?): SandboxEngine;

Defined in: packages/core/src/core/initFusion.ts:273

Create a standalone SandboxEngine for advanced use cases.

Use when you need direct control over the sandbox lifecycle, or when calling it from custom middleware/handlers.

Parameters

Parameter	Type	Description
config?	SandboxConfig	Optional sandbox configuration

Returns

SandboxEngine

A new SandboxEngine instance

Example

const sandbox = f.sandbox({ timeout: 3000, memoryLimit: 64 });
const result = await sandbox.execute(
    '(data) => data.filter(d => d.risk > 90)',
    records,
);
sandbox.dispose();

---

stateSync()

stateSync(): StateSyncBuilder;

Defined in: packages/core/src/core/initFusion.ts:241

Create a fluent builder for centralized State Sync policies.

Returns

StateSyncBuilder