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Managed Agents — Common Client Patterns

Patterns you'll write on the client side when driving a Managed Agent session, grounded in working SDK examples.

Code samples are TypeScript — Python and cURL follow the same shape; see python/managed-agents/README.md and curl/managed-agents.md for equivalents.

1. Lossless stream reconnect

Problem: SSE has no replay. If the connection drops mid-session, a naive reconnect re-opens the stream from "now" and you silently miss every event emitted in between.

Solution: on reconnect, fetch the full event history via events.list() before consuming the live stream, and dedupe on event ID as the live stream catches up.

const seenEventIds = new Set<string>()
const stream = await client.beta.sessions.events.stream(session.id)

// Stream is now open and buffering server-side. Read history first.
for await (const event of client.beta.sessions.events.list(session.id)) {
  seenEventIds.add(event.id)
  handle(event)
}

// Tail the live stream. Dedupe only gates handle() — terminal checks must run
// even for already-seen events, or a terminal event that was in the history
// response gets skipped by `continue` and the loop never exits.
for await (const event of stream) {
  if (!seenEventIds.has(event.id)) {
    seenEventIds.add(event.id)
    handle(event)
  }
  if (event.type === 'session.status_terminated') break
  if (event.type === 'session.status_idle' && event.stop_reason.type !== 'requires_action') break
}

2. processed_at — queued vs processed

Every event on the stream carries processed_at (ISO 8601). For client-sent events (user.message, user.interrupt, user.tool_confirmation, user.custom_tool_result) it's null when the event has been queued but not yet picked up by the agent, and populated once the agent processes it. The same event appears on the stream twice — once with processed_at: null, once with a timestamp.

for await (const event of stream) {
  if (event.type === 'user.message') {
    if (event.processed_at == null) onQueued(event.id)
    else onProcessed(event.id, event.processed_at)
  }
}

Use this to drive pending → acknowledged UI state for anything you send. How you map a locally-rendered optimistic message to the server-assigned event.id is application-specific (typically via the return value of events.send() or FIFO ordering).

3. Interrupt a running session

Send user.interrupt as a normal event. The session keeps running until it reaches a safe boundary, then goes idle.

await client.beta.sessions.events.send(session.id, {
  events: [{ type: 'user.interrupt' }],
})

// Drain until the session is truly done — see Pattern 5 for the full gate.
for await (const event of stream) {
  if (event.type === 'session.status_terminated') break
  if (
    event.type === 'session.status_idle' &&
    event.stop_reason.type !== 'requires_action'
  ) break
}

Reference: interrupt.ts — sends the interrupt the moment it sees span.model_request_start, drains to idle, then verifies via sessions.retrieve().

4. tool_confirmation round-trip

When the agent has permission_policy: { type: 'always_ask' }, any call to that tool fires an agent.tool_use event with evaluated_permission === 'ask' and the session goes idle waiting for a decision. Respond with user.tool_confirmation.

for await (const event of stream) {
  if (event.type === 'agent.tool_use' && event.evaluated_permission === 'ask') {
    await client.beta.sessions.events.send(session.id, {
      events: [{
        type: 'user.tool_confirmation',
        tool_use_id: event.id,         // not a toolu_ id — use event.id
        result: 'allow',               // or 'deny'
        // deny_message: '...',        // optional, only with result: 'deny'
      }],
    })
  }
}

Key points:

  • tool_use_id is event.id (typically sevt_...), not a toolu_... ID.
  • result is 'allow' | 'deny'. Use deny_message to tell the model why you denied — it gets surfaced back to the agent.
  • Multiple pending tools: respond once per agent.tool_use event with evaluated_permission === 'ask'.

Reference: tool-permissions.ts.

5. Correct idle-break gate

Do not break on session.status_idle alone. The session goes idle transiently — e.g. between parallel tool executions, while waiting for a user.tool_confirmation, or while awaiting a user.custom_tool_result. Break when idle with a terminal stop_reason, or on session.status_terminated.

for await (const event of stream) {
  handle(event)
  if (event.type === 'session.status_terminated') break
  if (event.type === 'session.status_idle') {
    if (event.stop_reason.type === 'requires_action') continue // waiting on you — handle it
    break // end_turn or retries_exhausted — both terminal
  }
}

stop_reason.type values on session.status_idle:

  • requires_action — agent is waiting on a client-side event (tool confirmation, custom tool result). Handle it, don't break.
  • retries_exhausted — terminal failure. Break, then check sessions.retrieve() for the error state.
  • end_turn — normal completion.

6. Post-idle status-write race

The SSE stream emits session.status_idle slightly before the session's queryable status reflects it. Clients that break on idle and immediately call sessions.delete() or sessions.archive() will intermittently 400 with "cannot delete/archive while running."

Poll before cleanup:

let s
for (let i = 0; i < 10; i++) {
  s = await client.beta.sessions.retrieve(session.id)
  if (s.status !== 'running') break
  await new Promise(r => setTimeout(r, 200))
}
if (s?.status !== 'running') {
  await client.beta.sessions.archive(session.id)
} // else: still running after 2s — don't archive, let it settle or escalate

7. Stream-first, then send

Always open the stream before sending the kickoff event. Otherwise the agent may process the event and emit the first events before your consumer is attached, and you'll miss them.

const stream = await client.beta.sessions.events.stream(session.id)
await client.beta.sessions.events.send(session.id, {
  events: [{ type: 'user.message', content: [{ type: 'text', text: 'Hello' }] }],
})
for await (const event of stream) { /* ... */ }

The Promise.all([stream, send]) shape works too, but stream-first is simpler and has the same effect — the stream starts buffering the moment it's opened.

8. File-mount gotchas

The mounted resource has a different file_id than the file you uploaded. Session creation makes a session-scoped copy.

const uploaded = await client.beta.files.upload({ file, purpose: 'agent_resource' })
// uploaded.id         → the original file
const session = await client.beta.sessions.create({
  /* ... */
  resources: [{ type: 'file', file_id: uploaded.id, mount_path: '/workspace/data.csv' }],
})
// session.resources[0].file_id !== uploaded.id  ← different IDs

Delete the original via files.delete(uploaded.id); the session-scoped copy is garbage-collected with the session. mount_path must be absolute — see shared/managed-agents-environments.md.

9. Secrets for non-MCP APIs and CLIs — keep them host-side via custom tools

Problem: you want the agent to call a third-party API or run a CLI that needs a secret (API key, token, service-account credential), but there is currently no way to set environment variables inside the session container, and vaults currently hold MCP credentials only — they are not exposed to the container's shell. So curl, installed CLIs, or SDK clients running via the bash tool have no first-class place to read a secret from.

Solution: move the authenticated call to your side. Declare a custom tool on the agent; when the agent emits agent.custom_tool_use, your orchestrator (the process reading the SSE stream) executes the call with its own credentials and responds with user.custom_tool_result. The container never sees the key.

// Agent template: declare the tool, no credentials
tools: [{ type: 'custom', name: 'linear_graphql', input_schema: { /* query, vars */ } }]

// Orchestrator: handle the call with host-side creds
for await (const event of stream) {
  if (event.type === 'agent.custom_tool_use' && event.name === 'linear_graphql') {
    const result = await linear.request(event.input.query, event.input.vars) // host's key
    await client.beta.sessions.events.send(session.id, {
      events: [{ type: 'user.custom_tool_result', tool_use_id: event.id, result }],
    })
  }
}

Same shape works for gh CLI, local eval scripts, or anything else that needs host-side auth or binaries.

Security note: this does not expose a public endpoint. agent.custom_tool_use arrives on the SSE stream your orchestrator already holds open with your Anthropic API key, and user.custom_tool_result goes back via events.send() under the same key. Your orchestrator is a client, not a server — nothing unauthenticated is listening.

Do not embed API keys in the system prompt or user messages as a workaround. Prompts and messages are stored in the session's event history, returned by events.list(), and included in compaction summaries — a secret placed there is durably persisted and readable via the API for the life of the session.