Delegate Handoff

Delegate handoff contract

delegate({goal, handoff, mcpServers?, skills?}) spawns a sub-agent in-process. The child runs its own streamText loop and returns a compact {ok, answer | reason, toolsUsed} envelope. This skill is the contract for how to use it well — the chat trajectory that motivated the system-skills remodel called delegate 5+ times without ever pushing skills, and the child ran context-blind every time.

What the child sees

Critical: the child can only use what you push. There's no discovery mechanism inside the child.

Always pass skills for non-trivial sub-tasks

If the sub-task involves a domain skill the parent has visible — GitHub queries, Gmail composing, workspace API patterns — push the skill. The child runs blind otherwise.

delegate({
  goal: "Find stale issues + PRs in the friday-platform org",
  handoff: "Today is 2026-05-12. Cutoff: 2026-05-10 (today - 2 days). " +
           "Run searches across friday-studio, friday-studio-examples, agent-sdk. " +
           "Return JSON of {repo, number, title, author, created}.",
  mcpServers: ["github"],
  skills: [
    { name: "@friday/using-mcp-servers" },
    // surgical: only the references you need, not the full body
    { name: "@friday/friday-cli", refs: ["references/recipes.md"] },
  ],
})

Skill resolution: only skills the parent has visible can be pushed. Out-of-scope skills are dropped + logged. The runtime resolves the skill body at the parent boundary and injects it into the child's system prompt as a <skills> block.

refs: for surgical injection

If a skill has reference files (e.g. references/phrases.md, references/anti-patterns.md), you can push only specific files instead of the whole SKILL.md body. The child sees one <file path="..."> block per requested ref.

Use this when:

• The full skill body is large and you need only a subset.
• The child's system prompt budget is tight.
• A specific reference file directly answers the sub-task.

mcpServers: — explicit allowlist

If you pass mcpServers, the child can only use tools from those servers. If you don't pass it, the child gets the parent's full MCP tool surface. Pass it when the sub-task is scoped (e.g. "GitHub-only research") to prevent the child from wandering into unrelated tools.

Budget envelope

The defaults (in packages/core/src/delegate/index.ts):

• max_steps_per_call: 40 — generous; rarely the limit.
• max_output_tokens: 20_000 — high so the child can produce detailed answers.
• max_depth: 1 — child cannot delegate further by default.

Workspaces can override via delegation: block in workspace.yml or per-job in jobs.<name>.delegation:. Job-level wins per field over workspace-level.

Writing a good handoff

The child has no chat history. The handoff is the only context. Good handoffs:

• State the goal in one sentence. "Find stale issues..." not "Help me understand what's stale."
• Encode the time anchor. "Today is 2026-05-12. Cutoff: 2026-05-10." Without this the child guesses.
• Specify the output shape. "Return JSON of {repo, number, ...}." Without this the child invents a format.
• Surface workspace context. "The repos are friday-studio, friday-studio-examples, agent-sdk in the friday-platform org." The child doesn't know your workspace.
• Don't restate prompt-injection guards. The child inherits those from the platform prompt scaffolding.

Bad handoffs (what the chat trajectory did):

goal: "Find the right org for these repos"
handoff: "The user is ken@tempest.team. Try each org."

Result: the child spends 12 tool calls brute-forcing get_teams + search_repositories × 3. With workspace introspection in the handoff or as a skill, it would have done one call.

Return contract

The child returns one of:

{ ok: true, answer: string, toolsUsed: [{name, outcome}, ...] }
{ ok: false, reason: string, toolsUsed: [{name, outcome}, ...] }

answer for success; reason for failure (impossible task, missing auth, unrecoverable error). Both shapes carry a tools manifest for observability.

When to delegate vs call inline

Delegate when:

• The sub-task needs many tool calls (5+).
• The output is bulky (long enough to bloat the parent's context).
• The work is independent and bounded (the child won't need to ask the user follow-up questions).

Call inline when:

• The task is one or two tool calls (get_me, list_jobs).
• The output is small.
• The work depends on subsequent parent decisions.

Bad delegate cases:

• "Look up the workspace's GitHub org" — that's describe_workspace(id).integrations.github.org, one call.
• "Format this markdown" — pure transformation, no tools needed.

Cross-references

• @friday/agent-action-handshake — sibling contract for the FSM action ↔ agent boundary.
• @friday/using-mcp-servers — MCP-tool allowlist semantics for the mcpServers: arg.
• @friday/debugging-broken-jobs — what to load when a delegate sub-task returns garbage.