Errors & pagination

Reference

Greenlight’s MCP tools and webhooks use the same conventions for errors and pagination. One page; every surface works the same way.

Error envelope

Every error response — REST, MCP, webhook delivery failure — uses this flat shape:

{
  "code": "app.slug_in_use",
  "message": "An app with slug 'expense-tracker' already exists in this organization.",
  "details": { "slug": "expense-tracker" },
  "next_steps": "Pick a different slug, or ask the current owner to add you as a co-owner.",
  "request_id": "req_01HXYZ4M2P"
}

code is stable across versions and uses <domain>.<reason> snake_case. Clients should switch on code, not on message.
message is human-readable, one sentence. Greenlight reserves the right to improve wording.
details (optional) carries structured, code-specific context — which field failed validation, which check failed in the policy gate, and so on.
next_steps (optional) is an actionable hint for the caller.
request_id is unique per request. Including it in a support ticket gets to the root cause fastest.

Over MCP the same body comes back as JSON text inside content, with isError: true and no structuredContent — a tool’s advertised output schema describes its success payload, so an error body (which doesn’t match that shape) never goes in structuredContent. Parse content[0].text as JSON to get code / message / next_steps / request_id.

HTTP status mapping

HTTP	When
`400`	Input failed validation, or a connected-database query/response shape was rejected. `details` identifies ownership and retry safety for SQL calls.
`401`	No valid session, bearer token, or required actor token. `details.issuer` identifies the configured identity provider when known. Code is `auth.token_invalid` (missing/malformed) or `auth.token_expired` (TTL elapsed — re-authenticate).
`403`	Authenticated, but the caller isn’t authorized for this action.
`404`	The target resource doesn’t exist or the caller can’t see it.
`409`	The action conflicts with current state (e.g. a slug in use, or a stale Knowledge `base_version`).
`429`	The caller’s bucket is exhausted. `Retry-After` indicates when to retry. `details.retry_after_ms` carries the same value in milliseconds.
`413`	The explicit request-body cap was exceeded (`validation.body_too_large`).
`499`	The caller disconnected while connected-database work was queued or active. This is a Greenlight response code for observability, not proof that a write rolled back.
`500`	A platform error. The audit log captures these; report with the `request_id`.
`502`	An external dependency or its network/auth path failed. Retry only when the code’s contract says the operation is replay-safe; SQL errors state this explicitly.
`503`	A bounded platform resource is temporarily full. The SQL gateway returns `proxy.query_capacity` with `Retry-After`.

Error code catalog

The most common stable codes. Not exhaustive; the full set lives in the platform’s shared error module.

Code	Meaning
`app.slug_in_use`	Another app in the org already owns this slug.
`app.not_found`	The app doesn’t exist or the caller can’t see it.
`app.not_owned`	Authenticated, but the caller isn’t an owner or co-owner of this app.
`app.invalid_slug`	Slug doesn’t match the required pattern.
`app.not_deployed`	The app has no live deployment URL yet (e.g. a preview URL was requested before first deploy).
`app.unreachable`	`curlApp` could not complete an HTTP response from the deployed app. Check diagnostics and logs; `details.hit_app` says whether a response began before the failure.
`permission.scope_denied`	Proxy call to an integration the app isn’t granted.
`permission.pending`	The app used an integration whose grant is still in IT review.
`proxy.actor_token_required`	A user-delegated integration call omitted the actor token.
`proxy.query_failed`	A connected-database `/query` statement was rejected by the database itself (syntax, permission, cast); the message is the database’s own.
`proxy.query_timeout`	A connected-database `/query` statement exceeded the execution-time cap. Narrow it; do not replay a possible write based on this code alone.
`proxy.query_result_unsupported`	A query returned a second result grid, too many columns, or an unsafe/unbounded native type. Reshape the result or cast to a bounded scalar type.
`proxy.query_capacity`	The SQL execution bulkhead is full. The statement did not start; honor `Retry-After`.
`proxy.query_canceled`	The caller disconnected while SQL work was queued or active. Inspect `execution_outcome` before reasoning about a write.
`proxy.upstream_unreachable`	The connected database or another upstream could not be reached. SQL responses mask the driver message and carry structured ownership/outcome fields.
`internal.audit_unavailable`	Greenlight could not persist the required SQL audit event. The database operation may already have committed.
`internal.unexpected`	Unexpected platform fault; internal detail is masked. Report the `request_id`.
`ai.model_denied`	The AI request used a model alias not granted to the app.
`auth.session_expired`	The session token expired or was revoked.
`auth.token_invalid`	No valid bearer token or the token is malformed/revoked.
`auth.token_expired`	The bearer token’s TTL elapsed; re-authenticate via the agent plugin.
`rate_limit.exceeded`	The caller’s bucket is exhausted.
`env.reserved_name`	`envSet` tried to set a platform-owned name (e.g. `DATABASE_URL`).
`env.policy_denied`	Org policy blocked the env operation.
`validation.body_invalid`	Request body failed validation; `details` carries the issue path.

Connected-database query errors

Every Azure SQL gateway error adds a stable decision record under details:

Field	Meaning
`fault_origin`	The responsible boundary: `request` (caller SQL/shape), `policy` (grant or database-role denial), `connected_database` (the upstream database), `platform` (Greenlight), or `unknown` when the boundary cannot prove responsibility.
`retryable`	The same logical operation could plausibly succeed later. This is not permission to replay it.
`safe_to_retry`	Replaying the identical request cannot duplicate a side effect. Automatically retry only when this and `retryable` are both `true`.
`execution_outcome`	`not_started` or `unknown`. Once execution may have begun, Greenlight does not claim commit or rollback certainty.
`database_code`	The SQL Server error number when available. Switch on this field, not database-message prose.

This is how a client distinguishes platform fault from its own fault: fault_origin: "platform" means Greenlight failed; "request" means the submitted query or result shape needs correction; "policy" means the operation is not allowed; and "connected_database" identifies the external database. "unknown" is intentional when a transport boundary cannot assign blame safely. The same request_id appears in the error body and X-Request-Id response header and correlates to Greenlight logs and audit.

Idempotency

Mutating MCP tools accept an idempotency_key. A retried call with the same key and payload returns the original response rather than performing the work twice. Use a fresh UUID v4 per logical operation, and reuse the same one only for retries of that operation.

Pagination

List endpoints — REST and MCP — use opaque cursor pagination, not offset/limit. Offsets are unsafe under concurrent inserts (they double-count or skip) and get expensive at large offsets. They accept limit (default 20, max 100) and cursor; the response includes next_cursor, or null on the last page.

{
  "items": [ /* … */ ],
  "next_cursor": "eyJrIjoiMjAyNi0wMy0xMlQxNDowODoxMVoiLCJpZCI6IjhhM2IxYzRmIn0="
}

To paginate forward, pass next_cursor back as cursor. To start from the beginning, omit cursor. There is no offset parameter.

Cursors are opaque: they encode the position needed to resume the query, but the encoding is not part of the API contract. Do not parse a cursor; do not generate one.

Stable sort

Each list has a defined sort key — documented per endpoint in the platform API conventions — with a stable tiebreaker so an item appears exactly once during a sustained pagination even as others are added concurrently. Many lists are newest-first by creation time; the apps catalog is newest-deploy first (never-deployed apps last). The cursor encodes that position; you never sort client-side.

MCP tools The tools these conventions apply to.

Observability & audit The audit-log webhook uses the same envelope for delivery errors.