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You attach a file set to an agent with the sandbox option on defineAgent(). Pass defineSandbox({ files }) to copy a set from src/files/ into the agent’s /workspace/agent directory before each prompt, where the agent can read them like local files.

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Use the agent’s own set

The simplest case: files: true on defineSandbox() uses the file set whose folder name matches the agent’s slug.
src/agents/support.ts
import { defineAgent } from "@keystrokehq/keystroke/agent";
import { defineSandbox } from "@keystrokehq/keystroke/sandbox";

export default defineAgent({
  slug: "support",
  systemPrompt: "Read /workspace/agent/product-guide.md before answering.",
  model: "anthropic/claude-sonnet-4.6",
  sandbox: defineSandbox({ files: true }), // uses src/files/support/
});
This expects a folder at src/files/support/. If it doesn’t exist, the agent fails to build with an “unknown file set” error.

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Use a named set

Pass a string to use a different set, useful when several agents share the same documents: 
import { defineSandbox } from "@keystrokehq/keystroke/sandbox";

export default defineAgent({
  slug: "support",
  systemPrompt: "Read the support handbook before answering.",
  model: "anthropic/claude-sonnet-4.6",
  sandbox: defineSandbox({ files: "support-handbook" }), // uses src/files/support-handbook/
});
A shared set lives at src/files/{name}/ and can be attached to any number of agents.

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Where files land at runtime

The set’s folder layout is preserved under /workspace/agent: 
src/files/support/product-guide.md        →  /workspace/agent/product-guide.md
src/files/support/context/seed.txt        →  /workspace/agent/context/seed.txt
Reference the paths the agent should read from the systemPrompt so the agent knows they’re there: 
systemPrompt:
  "Read /workspace/agent/product-guide.md and /workspace/agent/support-instructions.md first.",
Seeding is idempotent: files are written once per session, and any edits the agent makes during a run are preserved.

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Verify it

After deploying, prompt the agent and confirm it’s using the files: 
keystroke deploy --project <slug>   # or --filter agents/support
keystroke agents prompt support --message "What is our refund window?"

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Next steps

Files overview

What files are and how they differ from skills.

Attach skills to agents

Add reusable playbooks alongside files.

Build agents

Configure models, tools, skills, and files.

Run agents

Prompt agents and inspect their sessions.