Errors & sequencing

Every error string the wire returns, and the ordering guarantees you can rely on.

Error shape

Channel replies — phx_reply with status: "error":

{ "status": "error", "response": { "reason": "<string>" } }

HTTP — capability issuer, chat REST, dashboard:

{ "errors": [{ "status": "401", "title": "Unauthorized", "detail": "..." }] }

HTTP — Durable Objects operation failures:

{ "error": "<string>" }

`reason`	Channel	Cause
`invalid token`	any	capability token bad, expired, wrong signature, or bound to a different socket
`forbidden: missing channel:subscribe:{channel}`	PubSub	token doesn't grant subscribe on this channel
`forbidden: missing object:read:{type}/{key}`	Durable Object	token doesn't grant read on this object
`forbidden: missing chat:subscribe:{threadId}`	Chat	token doesn't grant subscribe on this thread
`auth required for private/presence channels`	PubSub	`private-` / `presence-` join with no `auth`
`auth required for durable object channels`	Durable Object	no `auth` and no `app_secret`
`auth required`	Chat	app has `enable_user_authentication = 1` and no token
`invalid app_secret`	Durable Object	wrong `app_secret`
`invalid secret`	Chat	agent join with a wrong `secret`
`app_key mismatch`	any	topic's `{appKey}` segment ≠ the connected app
`invalid topic format`	any	malformed topic

`reason`	Push	Cause
`Client messages are disabled`	PubSub publish	app has Enable Client Messages off
`Channel mode does not permit publishing`	PubSub publish	publishing on a channel whose token/mode forbids it
`Rate limit exceeded`	PubSub publish	over `max_client_events_per_sec`
`Validation failed: {detail}`	PubSub publish	payload failed channel validation (name / size limits)
`forbidden: missing {verb}`	Chat push	principal lacks the capability the push needs
`not_found`	Chat `cancel`	`runId` not in this thread
`already_ended`	Chat `cancel` / agent `run:end`	run is already terminal
`forbidden`	Chat `cancel`	not the run owner, and no `publish:cancel_any`
`invalid_state`	agent `run:suspend` / `run:resume`	run not in the required prior state
`archive_unavailable`	Chat `load_older`	an archived page couldn't be fetched
`writes must go through the server SDK`	Durable Object channel	any client push (the channel is read-only)

Status	Where	Cause
`401`	any server call	missing / wrong `X-App-Key` / `X-App-Secret`, or the path `app_id` isn't the authenticated app
`422`	`POST /api/auth`	missing `socket_id` / `client_id`, empty capability list, or a malformed capability string
`422`	Durable Object op	`increment` on a non-numeric slot, `append` on a non-list, bad transaction op
`404`	Durable Object	route not matched, or `GET /{slot}` for an unset slot
`429`	`trigger` / publish	over `max_backend_events_per_sec`

Cursors

Product	Cursor	Monotonic	Total order
PubSub	`serial` (per channel)	yes	yes, within a channel
Durable Objects	`log_id` (per object)	yes	yes, across all subscribers
Chat	`log_id` (per thread)	yes	yes, across all subscribers
Spaces	—	—	no ordering; pure relay

Guarantees

A snapshot reflects state exactly at its log_id. Live events resume at log_id + 1 — nothing between is dropped or duplicated.
after_serial / after_log_id replay is exact and in order, delivered before the snapshot (Durable Objects, Chat) or before live delivery (PubSub).
Chat: run:end is always emitted before its companion batch. The GC compaction batch is atomic — all four slot changes arrive together.
Durable Objects: a batch from set_all / transaction is atomic.
PubSub: message order within a channel matches publish order; across channels there is no ordering.

Not guaranteed

Ordering of events across different channels / objects / threads on one socket.
Delivery of Spaces events missed while disconnected.
Live presence:join / presence:leave on ephemeral-* channels (not yet broadcast — see Spaces).