Sessions

Run a session, stream its events, and handle the errors it can throw.

A session is one agent run, in its own sandbox, on its own git branch. kortix.session(projectId, sessionId) returns the handle for everything a session does: start it, send prompts, stream events, and read status. This page covers the handle, the readiness handshake, streaming, and the typed errors an SDK call can throw.

const s = kortix.session(projectId, sessionId);

s is the handle for everything a session does. The session ID, the sandbox ID, and the branch name are the same value. See Sessions for the concept.

Session lifecycle

Use the streamed method when the caller displays reload progress:

await s.reloadConfigStream({ refresh_repo: false }, (event) => {
  if (event.type === 'phase') console.log(event.phase);
});

The phases are checking-session, refreshing-workspace, compiling-config, applying-config, and confirming-config. The server omits refreshing-workspace when refresh_repo is false. The applying-config phase includes the daemon’s validated runtime replacement.

Three more read methods round out the handle:

• s.previews() — candidate preview ports the runtime exposes.
• s.publicShares.list() / .create(input) / .revoke(shareId) — public share links.
• s.audit(limit?) — the session’s audit trail of agent actions.
• s.transcript(options?) — a compact server-side transcript (text and tool calls, no tool inputs or outputs). This works with a project-scoped session token.
• s.voiceTranscript(options?) — this session’s live voice-call transcript (spoken turns plus ask_kortix/run_command worker tool calls). Returns an empty list when the session has no live call, not a 404.

Readiness is a handshake

Before you send a prompt, call ensureReady(). It provisions the sandbox if needed, waits for the runtime to boot, and returns the resolved runtime.

const { opencodeSessionId, runtimeUrl, sandboxId } = await s.ensureReady();

On a cold boot, ensureReady() can throw RUNTIME_UNAVAILABLE. See Retry on a cold boot for what that means and how to retry.

s.send() and s.abort() call ensureReady() for you.

Seed a server-authorized OpenCode pin

A server-rendered React host can supply the OpenCode pin already persisted for the same Kortix session:

const session = useSession(projectId, sessionId, {
  initialOpenCodeSessionId: persistedSession.opencode_session_id,
});

The seed only hydrates cached transcript content while /start runs. It does not override the runtime identity. The pin returned by /start is authoritative and replaces a stale seed.

Do not accept this value from an untrusted tenant selector. Do not create an OpenCode session in the host. Kortix creates and persists the root session. OpenCode query caches and transcript controllers are scoped to the sandbox runtime, so equal OpenCode ids from different sandboxes do not share cache entries.

Pending message retries keep their originating sandbox URL when you switch sessions. A 404 or 410 message response stops automatic retries without clearing the transcript. An explicit reconciliation can retry the read and restore normal synchronization after a successful response.

Send a prompt

s.setModel({ providerID, modelID }); // sticky for later send() calls
s.setAgent('build'); // sticky for later send() calls

await s.send('Refactor the auth module');
await s.send('One-off task', { model, agent }); // overrides for this call only
await s.abort(); // stop the current run

For OpenCode REST sessions, the first send() on a handle reads the model and agent persisted on the Kortix session. This prevents a snapshot-inherited OpenCode session from reusing stale snapshot defaults.

Prompt choice precedence is:

1. The send() call.
2. The handle’s setModel() or setAgent() value.
3. The persisted Kortix session default.

setModel only chooses what the next local send asks for — it never leaves the handle. To persist a new model for a running session server-side, use changeModel:

const { applied_live } = await s.changeModel('anthropic/claude-opus-4-8');

Restarting the runtime is how the change takes effect, so an in-flight turn ends. applied_live is true when a running session took it now, false when it applies at the next start. Only the session owner, or a caller with project-manager permissions, may change the model; anyone else gets 403.

send() resolves the runtime, then prompts it. abort() stops the current run without deleting the session.

Session scope and cost

Read the stored secret narrowing and materialized connection bindings. secrets_allowlist: null means the agent’s secret grant applies:

const scope = await s.scope();
scope.connector_bindings_configured; // false = inherits the project defaults

connector_bindings is the RESOLVED map, so it looks the same for a session that overrode its connectors and one that inherits the project defaults. Read connector_bindings_configured to tell them apart before rendering the scope or sending it back.

Replace one or both scope fields:

await s.rescope({
  secrets: ['DATABASE_URL'],
  connector_bindings: {
    github: { connection_id: connectionId },
  },
});

Each supplied field replaces its complete previous value. Omit a field to leave it unchanged. Connection changes apply to the next tool call. Secret removal stops future delivery but cannot remove an already disclosed value from model context or an existing process.

Both axes have an explicit way back to the default. They are not the same as an empty value:

await s.rescope({
  secrets: null, // inherit the agent's secret grant
  connector_bindings: null, // drop the override; inherit the project defaults
});

secrets: [] and connector_bindings: {} are the opposite instruction: an explicit “no project secrets” and “no connectors at all”, project defaults included. A session that sends {} where it meant null fails closed on every alias it did not name.

Read the unified cost record:

const cost = await s.cost();

The record combines finalized LLM cost, billed sandbox compute cost, model usage, token totals, compute duration, and ledger entries. s.cost() does not call ensureReady().

Runtime status and previews

const { ok, health } = await s.health();
const url = s.previewUrl(3000, '/docs');

s.health() never throws. Call it any time, even before the session has a runtime. s.previewUrl() and s.proxyUrl() need a resolved runtime — call s.ensureReady() first, or they throw SessionNotReadyError. See Session readiness errors.

Streaming

Use s.stream() to receive live events in a script or server. In a React app, use useSession instead — it manages the whole session lifecycle for you.

s.stream() is the OpenCode REST compatibility event stream. The Kortix API proxies it from the sandbox. There is no separate WebSocket endpoint. The transport is fetch with a streaming response body, read through ReadableStream and TextDecoderStream. The SDK handles reconnection, backoff, and a heartbeat check.

Stream a session:

1. Call ensureReady() first. The runtime does not exist until the sandbox starts.
2. Open the stream before you send a message, so you do not miss early events.
3. Send the message.
4. Close the stream when you see session.idle.

const session = kortix.session(projectId, sessionId);
const { opencodeSessionId } = await session.ensureReady();

const stream = await session.stream({
  onEvent: (event) => {
    if (event.type === 'session.idle' && event.properties.sessionID === opencodeSessionId) {
      onTurnDone();
      stream.close();
    }
  },
});

await session.send('Refactor the auth module');

Streaming needs fetch with a real ReadableStream body and TextDecoderStream. Browsers, Node 18 and later, Bun, and Cloudflare Workers all support it. React Native and Expo do not: their fetch has no response.body. On React Native, use createHttpSessionSyncController for bounded history and status synchronization. Use a platform-specific event transport for live events.

The controller loads the newest 10 messages first. loadOlder() follows the server cursor. loadHttpSessionHistory() follows every cursor for explicit exports.

Event types

Each event has a type and a properties object that holds its data, for example event.properties.sessionID.

Turn raw messages and parts into renderable output with classifyTurn. See SDK reference.

Retry on a cold boot

ensureReady() polls the session’s /start endpoint — each call long-polls up to 30 s — until the runtime reaches a terminal ready/failed/stopped stage or its deadline (readyTimeoutMs, default ~180 s) elapses. On a warm session the first poll resolves ready immediately. On a cold boot it keeps polling while the sandbox reports retriable: true, so a slow start just takes longer rather than throwing. It only throws an ApiError with code: 'RUNTIME_UNAVAILABLE' if the runtime is still not ready when the deadline expires.

ensureReady() is idempotent, so concurrent calls for the same session share one /start request instead of sending several. The retryUntilReady helper below is now optional — ensureReady() already retries internally — but stays useful if you want a longer total budget than the default readyTimeoutMs.

async function retryUntilReady<T>(ensure: () => Promise<T>): Promise<T> {
  const deadline = Date.now() + 300_000;
  for (;;) {
    try {
      return await ensure();
    } catch (error) {
      const provisioning = error instanceof ApiError && error.code === 'RUNTIME_UNAVAILABLE';
      if (!provisioning || Date.now() > deadline) throw error;
      await new Promise((r) => setTimeout(r, 3_000));
    }
  }
}

See Error classes for the full ApiError shape. In React, useSession retries /start for you, so you do not need this pattern.

What /start tells you

Every /start answer describes that call, not the row’s accumulated history. Four fields carry it.

boot.actively_starting answers “is a provider operation running for this session right now?”. A starting payload with actively_starting: false means the server is waiting out a retry cooldown, not that a box is booting.

{
  "stage": "starting",
  "retriable": true,
  "reason": "runtime_wake_cooldown",
  "observed_at": "2026-08-26T14:00:00.000Z",
  "action": "cooling_down",
  "boot": { "phase": "resuming", "since": "2026-08-26T13:58:00.000Z", "actively_starting": false },
  "observation": {
    "provider": { "known": false, "status": null, "checked_at": null },
    "runtime": { "known": false, "state": null, "boot_phase": null, "checked_at": null }
  },
  "failure": {
    "category": "sandbox-provider",
    "message": "The runtime did not start (attempt 2). Retrying automatically.",
    "retryable": true,
    "evidence": {
      "check": "provider_not_running",
      "observed_at": "2026-08-26T13:58:00.000Z",
      "error": null,
      "attempts": 2,
      "next_retry_at": "2026-08-26T14:03:00.000Z"
    }
  }
}

A failed start is retried for you

A start that fails stamps a cooldown, not a permanent verdict. The next /start after the cooldown re-attempts the wake by itself. The cooldown grows with consecutive failures (2 min, 5 min, 10 min). After five consecutive failures /start answers stage: "failed" with the attempt count in failure.message; that verdict expires 30 minutes after the last failure, and POST …/restart clears it immediately.

retriable is derived on every call. A state the server can still re-attempt never carries retriable: false.

failure.evidence names the check that produced the negative, when it ran, and when the server retries. Every /start failure carries it.

Prompt attachments

Upload local files when users add them to a composer. Private uploads belong to the project and do not require a running session.

import { usePromptAttachments } from '@kortix/sdk/react';

const uploads = usePromptAttachments(projectId);
// File picker, paste, and drop handlers call uploads.add(file) or uploads.addMany(files).
// Render uploads.attachments. Refuse Send only while an attachment is `error` or `aborted`.

async function submit() {
  const ids = uploads.attachments.map((item) => item.id);
  uploads.submit(ids); // Send never waits: the composer clears and uploads continue.
  paintMessage(text, ids);
  try {
    const parts = await uploads.whenReady(ids);
    await kortix.session(projectId, sessionId).prompts.create({
      clientMessageId,
      messageId,
      parts: [{ type: 'text', text }, ...parts],
    });
    uploads.forget(ids);
  } catch {
    uploads.reclaim(ids);
  }
}

whenReady(ids, { signal }) resolves once every upload is ready, in ids order. It rejects when an upload fails, is aborted or removed, or signal aborts. submit(ids) hands the entries to that send: they leave attachments, stop counting toward the limits, and keep uploading after the composer unmounts. Call forget(ids) after the POST succeeds, or reclaim(ids) to return them to the composer after a failed send. The resolved file part contains attachment_id, filename, and mime. It contains no URL or file bytes. The server binds and materializes the upload. Use these parts on platform session creation, warm-session start, or prompt inbox routes. Do not pass private handles directly to OpenCode runtime sendParts. Legacy platform file parts with url still work.

Each item has a stable id, the original file reference, receivedBytes, and a status: pending, uploading, processing, ready, error, or aborted. Bytes sent determine progress. The controller publishes a progress snapshot only for a whole-percent change, at most ten per second per upload. processing can remain at 100% until the server completes the upload. Limits are 50 MiB per file, 100 MiB per message, and 20 files. Files must be nonempty. Two files upload concurrently by default.

retry(id) resumes the same handle. After attachment_size_mismatch or attachment_failed the server keeps no usable handle, so retry(id) uploads the File again as a new attachment. An expired upload cannot retry: retry(id) throws, and the item error carries code attachment_expired. abort(id) cancels unfinished work. remove(id) removes the entry, aborts its upload, and resolves at once. The server DELETE is best-effort and never rejects; an upload it cannot delete expires after 24 hours. forget(ids) releases entries without deleting server objects. The hook aborts listed work on unmount or project change and deletes its uploads best-effort: no send holds them, and drafts keep no handle. Handed-off uploads continue.

Selections live in memory only. Never persist File objects, blob URLs, signed URLs, or upload handles in a draft. Abandoned uploads expire after 24 hours.

Framework-free hosts use kortix.project(projectId).attachments.createController() with the same methods. Subscribe through subscribe(listener) and read getSnapshot(). Call dispose() when the composer closes. Direct callers can use attachments.upload(file, { signal, onProgress, onUpload, resume }) and attachments.delete(attachmentId). Retain onUpload metadata for manual same-ID resumption.

The server selects the transport in the handle’s upload field:

• kind: 'direct' is the default. The SDK sends the whole file in one PUT to upload.url with upload.headers and no Authorization header. With XMLHttpRequest (browsers, React Native), progress reports sent bytes. With fetch, progress reports 0 and then the full size. An expired URL, or one that Storage refuses with 400, 401, or 403, is re-signed once for the same attachment_id. A 409 from Storage means an earlier attempt stored the file.
• kind: 'chunked' sends sequential authenticated PUTs of upload.chunk_size bytes. The SDK accepts any positive chunk_size. Only a deployment whose edge drops large request bodies selects this mode.

Completion verifies the stored size and SHA-256. If completion answers 409 attachment_not_uploaded, onUpload reports the direct handle with received_bytes: 0, so retry(id) or a resume sends the file again. Initiation, the upload, and completion retry timeouts, network errors, 429, and 5xx with jittered exponential backoff. The budget is 60 seconds from the first failure, so a long upload that fails late still retries. Completion also retries attachment_processing, with a five-minute budget. Initiation never retries 402 (a BillingError: the account cannot run) or 429 attachment_budget_exceeded (40 unfinished uploads or 500 MiB of unsent uploads for the user; unused uploads expire within 24 hours). The server answers or refuses one completion within 105 seconds. Each completion request allows 120 seconds. Caller aborts never retry.

A sent attachment’s reference is released 1 hour after its prompt is delivered, and when its session or project is deleted. The next maintenance sweep then removes the file, and its attachment_id can no longer be sent.

Files

s.files reads and writes the session’s sandbox: list, read, readBlob, status, findFiles, findText, upload, create, copy, remove, mkdir, rename. Every call resolves the runtime first, and always targets this session’s own sandbox. See the SDK reference for the full method list.

The raw runtime

s.runtime is the typed OpenCode REST client. Use it only for calls that send, abort, and stream do not cover. It requires a resolved OpenCode runtime — call s.ensureReady() first.

const { opencodeSessionId } = await s.ensureReady();
await s.runtime.session.prompt({
  sessionID: opencodeSessionId,
  parts: [{ type: 'text', text: 'Refactor the auth module' }],
});

The OpenCode sessionID here is not the session ID you pass to kortix.session(projectId, sessionId). The SDK resolves it during ensureReady() and caches it on the handle.

Warm a project session

Call ensureWarm() when a project landing page needs one runtime ready before the first prompt.

const project = kortix.project(projectId);
const warm = await project.sessions.ensureWarm();

// An ORDINARY session. Prompt it like any other.
await kortix.session(projectId, warm.session.session_id).send("Build me a widget");

ensureWarm() creates, or returns, one unused session for the current user. It is the same create sessions.create() runs, with the project’s defaults: same billing gate, same concurrent-session cap, same connector requirements. The only difference is metadata.warm, which hides the session from sessions.list() until its first prompt lands.

Treat it as speculative. A 409 WARM_SESSION_UNAVAILABLE means the account has no concurrent-session headroom to spare or the project cannot be warmed right now — fall through to sessions.create(), which reports the real reason.

The warm session carries the project’s DEFAULT agent and sandbox. If the user picks a different one, abandon it and call sessions.create(): an unused warm session is hidden and reaped on its own.

Handling errors

Every call through createKortix rejects with a typed Error subclass, never a plain object. Catch the error, check instanceof, and branch on .status or .code.

import { ApiError, BillingError } from '@kortix/sdk';

try {
  await kortix.project(projectId).sessions.create();
} catch (err) {
  if (err instanceof BillingError) {
    // 402 — out of credits or over a plan limit
  } else if (err instanceof ApiError) {
    // any other failed request — err.status, err.code, err.detail
  } else {
    throw err;
  }
}

Error classes

ApiError.name is 'ApiError' by default. Two cases override it:

• name: 'AbortError', code: 'ABORTED' — the request was cancelled, for example by navigation. This is not a failure. Ignore it.
• code: 'TIMEOUT' — the request’s own timeout elapsed. url, endpoint, and timeout show what timed out.

For any other failure, status holds the HTTP status code. code comes from the backend’s error_code, or falls back to the status as a string. message is an enumerable own property on ApiError, so it survives JSON.stringify and object spread.

Kortix retries some requests before your code sees an error. If a GET or HEAD request returns 502, 503, or 504, Kortix retries it up to 2 times, with a 250ms then 500ms delay. A transient transport failure on a GET or HEAD — a network error, not a status code — is retried the same way. A retry that succeeds never reaches onError. Kortix never retries POST, PUT, PATCH, or DELETE requests, or a 500 response.

Kortix throws AuthError on the client, before it sends a request, when getToken() returns null. AuthError extends ApiError, so err instanceof ApiError still matches. Check err instanceof AuthError, or err.code === 'NO_SESSION', to treat “not signed in” as a separate case from a backend failure.

Kortix throws BillingError for every HTTP 402 response: out of credits, over a plan limit, or another billing gate. detail.message holds the reason from the backend.

Kortix throws RequestTooLargeError for HTTP 431. This usually means the request carried too many files. detail.suggestion holds a ready-to-show hint for the user.

Session readiness errors

Two errors mean the session’s sandbox is not ready yet. Handle each one differently.

SessionNotReadyError throws synchronously when you call a runtime accessor — session.previewUrl(), session.proxyUrl(), or session.runtime — before this session handle has resolved its sandbox. A session handle only resolves its own sandbox; it never falls back to another session’s sandbox.

import { SessionNotReadyError } from '@kortix/sdk';

const s = kortix.session(projectId, sessionId);
try {
  const url = s.previewUrl(3000); // throws: not resolved yet
} catch (err) {
  if (err instanceof SessionNotReadyError) {
    await s.ensureReady();
  }
}

Call await session.ensureReady() first, or call send(), which readies the session internally. session.health() is the one accessor that never throws this error, so you can poll it before the session boots.

RUNTIME_UNAVAILABLE is the second error — it means ensureReady() itself timed out waiting for a cold boot. See Retry on a cold boot for the full pattern. In React, useSession retries this for you and exposes it through the phase value instead of throwing.

Helpers

import { formatBillingErrorForUI } from '@kortix/sdk';

try {
  await kortix.session(projectId, sessionId).start();
} catch (err) {
  const ui = formatBillingErrorForUI(err);
  if (ui) showUpgradeModal(ui.alertTitle, ui.alertSubtitle);
}

In @kortix/sdk/react

@kortix/sdk/react re-exports BillingError, RequestTooLargeError, parseBillingError, isBillingError, and formatBillingErrorForUI. It does not re-export ApiError or AuthError — import those from @kortix/sdk.

useSession classifies every send, answerQuestion, answerPermission, and rejectQuestion failure into one sendError object, so you do not need to write instanceof checks by hand:

interface KortixSendError {
  kind: 'billing' | 'runtime-not-ready' | 'runtime-error';
  message: string;
  billing?: BillingError; // set when kind is 'billing'
  cause: unknown;
}

const s = useSession(projectId, sessionId);

if (s.sendError?.kind === 'billing') {
  const ui = formatBillingErrorForUI(s.sendError.billing);
}

See React hooks for the rest of useSession.