lamdera live: RPC responses containing fractional or negative JSON numbers fail with 'rpc response decoding failed'

[CharlonTank]

Any lamdera_handleEndpoints response whose JSON contains a fractional number (42.5, 0.1, 1e-3, ...) or a negative number (-5) makes lamdera live reply rpc response decoding failed for {...} instead of the response, even though the backend produced valid JSON. Non negative integer responses work fine. Requests containing such numbers are unaffected (they pass through as raw text); only responses break.

Deployed apps are not affected, which makes this extra confusing: the same endpoint works in production and only breaks on lamdera live.

Minimal repro

Full SSCCE with three endpoints (integer works, float and negative fail): https://github.com/CharlonTank/lamdera-rpc-nofloats-sscce

$ curl -s -X POST http://localhost:8002/_r/int-ok -H "Content-Type: application/json" -d '{}'
{
    "value": 42
}

$ curl -s -X POST http://localhost:8002/_r/float-bug -H "Content-Type: application/json" -d '{}'
rpc response decoding failed for {"t":"qr","r":"ead924cf-4a07-408c-bdb1-1fdb3623fa7d","c":200,"ct":"OK","h":{},"v":{"value":42.5}}

$ curl -s -X POST http://localhost:8002/_r/neg-bug -H "Content-Type: application/json" -d '{}'
rpc response decoding failed for {"t":"qr","r":"a98c5f2b-d569-4d96-9bbd-8db287575876","c":200,"ct":"OK","h":{},"v":{"value":-5}}

Note the echoed envelopes: they are valid JSON and carry the correct payloads. The bridge just cannot parse them.

Root cause

extra/Lamdera/CLI/Live.hs (around line 695 on lamdera-next) decodes the browser to server RPC response envelope with the compiler's internal JSON parser:

D.oneOf
    [ D.field "i" (D.value & fmap ...)
    , D.field "v" (D.value & fmap ...)   -- Json.Value re-parsed here
    , D.field "vs" (D.string & fmap ...)
    ]

That parser (compiler/src/Json/Decode.hs) was written for elm.json files and only accepts non negative integers: a . or an exponent raises the dedicated NoFloats parse error, and a leading - is not recognized at all. So the D.value extraction of the v field fails on the first such number anywhere in the response, and Live.hs falls into its Left jsonProblem -> "rpc response decoding failed for ..." branch.

I have a fix that teaches the parser full JSON number literals while keeping plain integers on the existing Int constructor (so all typed decoders used for elm.json behave exactly as before); PR incoming.