Errors

Every error is RFC 9457 Problem Details with a stable code. The codes, their statuses and params, and which routes return them.

The shape

{
  "type": "https://tools.ietf.org/html/rfc9110#section-15.5.10",
  "title": "Conflict",
  "status": 409,
  "detail": "Posts can only be edited within 60 minutes of posting.",
  "code": "post.edit_window_closed",
  "params": { "editWindowMinutes": 60 },
  "traceId": "00-…"
}

code is always present and never renamed. Match on it, and show your own (translated) message for it.
params holds the values a message needs, when there are any.
errors lists field problems on validation_failed and profile.invalid.
detail is English for developers and logs. Don’t show it to members or match on it.
traceId is what the server’s logs are keyed on; quote it when reporting a 500.

New codes may be added, so always fall back to a generic message for one you don’t recognise. The codes are defined in src/FeedFabric.Application/Errors/ErrorCodes.cs; the repository’s docs/errors.md is the canonical list.

Codes

Code	Status	Params	Meaning	Returned by
`validation_failed`	400		See `errors` below	Any route with a body or bounded parameters
`user.not_synced`	404	`externalUserId`	The signed-in user has no FeedFabric user yet	Member routes
`user.suspended`	403		Suspended: can read, but not post, comment, like, repost, follow, report or upload	Every member write except reading signals
`post.not_found`	404		No such post, deleted, or a repost’s own ID where an original is needed	Posts, likes, reposts, comments, reports, Not interested, Show more, moderation
`post.not_author`	403		Only the author can edit or delete a post	`PUT`/`DELETE /userfeed/posts/{id}`
`post.edit_window_closed`	409	`editWindowMinutes`	The 60-minute edit window has passed	`PUT /userfeed/posts/{id}`
`post.is_repost`	409		Reposts can’t be edited	`PUT /userfeed/posts/{id}`
`post.too_many_media`	400		More photos than `Media:MaxPerPost` (4)	`POST /userfeed/posts`
`comment.not_found`	404		No such comment, or deleted; also a missing parent comment	Comments, replies, comment reports, moderation
`comment.not_author`	403		Only the author can delete a comment	`DELETE /userfeed/comments/{id}`
`content.violation`	422	`category`	Breaks the community rules: `threat`, `blocked_term`, `link_spam`, `flooding`…	Creating and editing posts, commenting
`media.not_found`	404		No such upload, not yours, or already on another post	`/media/*`, `POST /userfeed/posts`
`media.not_ready`	409		A photo hasn’t finished its checks, or was rejected	`POST /userfeed/posts`
`media.type_not_allowed`	415	`allowed`	Only JPEG, PNG and WebP	`POST /media/uploads`
`media.too_large`	413		Over `Media:MaxUploadBytes`	`POST /media/uploads`
`media.wrong_state`	409		The upload was already completed	`POST /media/{id}/complete`
`user.not_found`	404	`externalUserId`	No user with that ID	Follows, favourites, `/ranking/preview`, `/admin/users/*`
`follow.self`	400		Can’t follow yourself	`/follows/{id}`
`favourite.self`	400		Can’t favourite yourself	`/favourites/{id}`
`favourite.limit_reached`	409	`max`	Already at 30 favourites	`PUT /favourites/{id}`
`profile.not_found`	404	`profile`	No ranking profile with that key	`/userfeed/foryou?profile=`, `/ranking/profiles/*`
`profile.read_only`	409	`profile`	Presets can’t be changed or deleted	`PUT`/`DELETE /ranking/profiles/{key}`
`profile.invalid`	400		Settings out of range, or a formula that doesn’t parse; `errors` lists `{ field, message, position? }`	`PUT /ranking/profiles/{key}`, `/ranking/preview`
`profile.invalid_key`	400	`profile`	Keys are 2–40 lowercase letters, digits and dashes, starting with a letter	`PUT /ranking/profiles/{key}`
`bad_request`	400		Generic fallback
`unauthorized`	401		Missing or invalid token	Every route
`forbidden`	403		Missing role (generic fallback)	Staff routes
`not_found`	404		Unknown route
`method_not_allowed`	405
`conflict`	409		Generic fallback
`unsupported_media_type`	415		Send `Content-Type: application/json`	Routes with a body
`internal_error`	500		Unexpected server error, including a safety model that couldn’t run; quote `traceId`	Any

Validation errors

{
  "status": 400,
  "code": "validation_failed",
  "errors": [
    { "field": "content", "code": "required" },
    { "field": "limit", "code": "out_of_range", "params": { "min": 1, "max": 100 } }
  ]
}

field is the camelCase field or parameter name, left out when the problem is the whole body (malformed JSON, say).

Field code	Params	Meaning
`required`		Missing or blank
`out_of_range`	`min`, `max`	Outside the allowed range (also too many items: `max` only)
`invalid_value`		Wrong format or type, or not one of the allowed values (a malformed ID, an unknown report reason)

Not Problem Details

Two kinds of response come from elsewhere and have no body to parse:

Signed blob URLs in development (/blobs/…): 403 for a bad or expired signature or the wrong Content-Type, 413 for too large, 404 for a missing file.
S3 (presigned URLs): the bucket’s own XML errors.