---
title: "Session Context"
description: "Runtime helpers: ctx.session, ctx.getSandbox, ctx.getSkill, and defineState."
---

Eve exposes runtime state through the `ctx` parameter passed to tool `execute`, hook handlers, and channel event handlers:

- `ctx.session`: session metadata, turn, auth, and parent lineage
- `ctx.getSandbox()`: live sandbox handle for the current agent
- `ctx.getSkill(identifier)`: handle for a named skill visible to the current agent
- `defineState(name, initial)`: typed durable state with `get()` and `update()` (imported from `eve/context`)

These APIs work only inside active authored runtime execution such as tools, channel event handlers, and authored hooks. They throw when called outside a managed context.

## `ctx.session`

Use `ctx.session` when you need durable runtime metadata about the current execution.

```ts title="agent/tools/who_called_me.ts"
import { defineTool } from "eve/tools";
import { z } from "zod";

export default defineTool({
  description: "Return the active session metadata.",
  inputSchema: z.object({}),
  async execute(_input, ctx) {
    return {
      sessionId: ctx.session.id,
      turnId: ctx.session.turn.id,
      turnSequence: ctx.session.turn.sequence,
      currentCaller: ctx.session.auth.current?.principalId,
      initiator: ctx.session.auth.initiator?.principalId,
      parentSessionId: ctx.session.parent?.sessionId,
      parentCallId: ctx.session.parent?.callId,
    };
  },
});
```

Public session fields:

- `auth.current`
- `auth.initiator`
- `id`
- `turn.id`
- `turn.sequence`
- optional `parent`

Important behavior:

- `auth.current` is the caller for the active inbound turn.
- `auth.initiator` is the caller that started the durable session.
- Unprotected agents expose both as `null`.
- Top-level schedule sessions expose the framework app principal (`principalId: "eve:app"`, `principalType: "runtime"`).
- `parent` is present for child subagent sessions and includes the parent `callId`, `sessionId`, `rootSessionId`, and `turn`.

## `ctx.getSandbox()`

`ctx.getSandbox()` returns a live handle for the current agent's sandbox.

```ts
const sandbox = await ctx.getSandbox();
const result = await sandbox.run({ command: "npm test" });
```

Important behavior:

- It takes no arguments: each agent has exactly one sandbox.
- It is async because Eve binds or restores sandbox state lazily.
- It only works when sandbox access is attached to the active runtime path.
- Visibility is node-local: a subagent sees its own sandbox, not the parent's.

`SandboxSession` also exposes `resolvePath(path)` for cases where authored code needs the live backend-native path for a logical `/workspace/...` location before passing it to shell code or a child process.

See [Sandbox](../sandbox) for lifecycle details.

## `ctx.getSkill(identifier)`

`ctx.getSkill(identifier)` returns a handle for a named skill visible to the current agent.

```ts
const skill = ctx.getSkill("research");
const notes = await skill.file("references/checklist.md").text();
```

Important behavior:

- It is synchronous; file content is read lazily from the active sandbox.
- It only works when sandbox access is attached to the active runtime path.
- `identifier` is the path-derived skill id.
- Visibility follows the current agent's sandbox.
- Missing skills surface when a file accessor reads a missing sandbox path.
- The returned handle exposes `name` and `file(relativePath)`.

See [Skills](../skills) for the full authoring model.

## Custom state with `defineState`

Use `defineState` when your agent needs durable typed state that tools, hooks, and channel handlers can share. State survives across workflow step boundaries. Declare the handle at module scope so every importer shares it:

```ts title="agent/lib/budget.ts"
import { defineState } from "eve/context";

interface BudgetState {
  readonly count: number;
  readonly cap: number;
}

export const budget = defineState<BudgetState>("myapp.budget", () => ({
  count: 0,
  cap: 25,
}));
```

`get()` reads the current value (returning `initial()` on first access), and `update(fn)` applies a function to it. Both throw outside a managed scope. See [State](./state) for the full read/write model and examples from tools and hooks.

## Where these APIs work

Safe places:

- inside `defineTool(...).execute(input, ctx)`
- inside authored callbacks Eve runs inside the runtime
- after asynchronous boundaries inside the same authored execution chain

Unsafe places:

- top-level module evaluation
- build scripts
- discovery-time code paths

If you call them outside an active Eve runtime context, they throw immediately with a message explaining the required scope.

## How it works

The framework sets up a context container before invoking authored code:

1. The runtime populates durable seed values (auth, session id, compiled bundle).
2. Before each step, the framework derives step-local values (session metadata, sandbox access, skill access) from the durable state.
3. Authored code runs inside the managed scope, so `ctx` and `defineState` accessors resolve automatically.
4. After the step, the framework commits mutable state (for example sandbox changes) back to the durable session.

This lifecycle is fully managed by the framework. Authored code only needs to use `ctx` and the public accessors.

## What to read next

- [State](./state)
- [Sessions, runs & streaming](../concepts/sessions-runs-and-streaming)
- [Subagents](../subagents)
- [Skills](../skills)
