Lexicon schema validation isn't generic #7

Attempting to post with "Allow quote posts" set to off in social-app will fail and result in a "Lexicon not found: lex:app.bsky.feed.postgate" message appearing at the top of the composer. Unclear what the cause is, last few logs after the attempt are:

2026-03-08T15:09:28.581715Z  INFO tranquil_pds::api::proxy: Proxying GET request to https://api.bsky.app/xrpc/app.bsky.actor.getProfile?actor=did%3Aplc%3Abpu2pz4q53tbdusav2je377x
2026-03-08T15:09:28.581894Z  INFO tranquil_pds::api::proxy: Proxying GET request to https://api.bsky.app/xrpc/app.bsky.actor.getProfile?actor=did%3Aplc%3Atzrpqyerzt37pyj54hh52xrz
2026-03-08T15:09:29.503903Z  INFO tranquil_pds::api::repo::record::batch: apply_writes called: repo=did:plc:bpu2pz4q53tbdusav2je377x, writes=3
2026-03-08T15:09:29.577748Z  INFO tranquil_pds::api::proxy: Proxying GET request to https://api.bsky.app/xrpc/app.bsky.draft.getDrafts

with the following response on the client:

{
    "error": "InvalidRecord",
    "message": "Lexicon not found: lex:app.bsky.feed.postgate"
}