fix(json): keep nested bytes/ints tagged in qvariantToNlohmann containers

[dlipicar]

Problem

A bstr method argument never reaches a cdylib (Rust) module — the callee decodes an empty Vec<u8> and, e.g., echoBytes(v) returns null.

Root cause is in qvariantToNlohmann (cpp/logos_json_convert.cpp). It ran the canConvert<QJsonObject>() / canConvert<QJsonArray>() fallbacks before the type-preserving QVariantList/QVariantMap recursion. A QVariantList/QVariantMap also reports canConvert<QJson…>() == true, so a container was routed through QJson — which has no byte type and degrades numerics to double. A nested QByteArray was flattened to a plain string, losing the canonical {"_bytes":"<base64url>"} tag. (Nested whole integers happened to survive — they serialize without a decimal point — which is why the existing int-preservation tests passed while bytes silently broke, and why the container recursion added earlier was effectively shadowed/dead for these types.)

How it bites

LogosProviderObject::callMethodStdBridge converts every call argument via qvariantToNlohmann. A bstr argument arrives (over QtRO) as a QByteArray nested inside the QVariantList of call args:

transport delivers:  QVariantList[ QByteArray("hello") ]
qvariantToNlohmann:   ["hello"]            ← tag lost (was [{"_bytes":"aGVsbG8"}])
cdylib bytes::decode: not a {"_bytes":…} object → None → empty Vec → echoBytes → null

The QtRO C++ path is unaffected (native QByteArray marshaling; Qt auto-converts QString↔QByteArray), and the plain-lp path was already correct and tested. Only the container-through-QVariant leg dropped the tag.

Fix

Move the container recursion (QStringList / QVariantList / QVariantMap) ahead of the QJson fallbacks, so nested elements recurse element-by-element — QByteArray → {"_bytes":…} (tagged), integers stay integers, etc. Only genuine QJson-typed QVariants reach the fallbacks now. One-block reorder; no behavior change for scalars or already-QJson variants.

Tests

• 3 new JsonConvertBytes unit tests: nested bytes in a list, nested bytes in a map, and the exact callMethodStdBridge shape (QVariantList[QByteArray] → [{"_bytes":…}] → re-decodes to QByteArray). All fail before / pass after.
• Full protocol suite: 163/163 pass (existing int-preservation and [tstr] tests unaffected).
• End-to-end: with this protocol built into logoscore, the Rust test_fullapi_rust.echoBytes 'json:{"_bytes":"aGVsbG8"}' now returns the bytes ({"_bytes":"aGVsbG8"}) instead of null; instrumentation confirmed callMethodStdBridge now yields [{"_bytes":"aGVsbG8"}] instead of ["hello"].

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR fixes lossless JSON conversion for QVariant containers so nested QByteArray (and integer) values remain type-preserved when converting through qvariantToNlohmann, which is critical for the Qt↔Rust cdylib bridge and other C-ABI consumers.

Changes:

• Reordered qvariantToNlohmann to run QStringList/QVariantList/QVariantMap recursion before the QJsonObject/QJsonArray conversion fallbacks, preventing nested bytes/ints from being coerced by Qt JSON.
• Added unit tests covering nested QByteArray inside lists/maps and a list-shaped argument case to ensure round-trip preservation via nlohmannArgsToQVariantList.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
cpp/logos_json_convert.cpp	Moves Qt JSON fallbacks after container recursion to preserve nested byte/int types during conversion.
tests/protocol/test_json_convert_bytes.cpp	Adds regression tests verifying nested bytes remain tagged and can round-trip back to QByteArray.

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[dlipicar]

Good catch on both — the code was fine but the test comments overstated the shape. Tightened them:

• callMethodStdBridge converts each argument individually, so a top-level QByteArray argument already hits the tagged case. The break is specifically an argument that is itself a QVariantList/QVariantMap containing a QByteArray — in the cdylib path, callModuleMethod's 3rd argument (the nested call-args list), which callMethodStdBridge hands to qvariantToNlohmann as a single QVariantList. Reworded the block comment to say exactly that.
• Dropped the "exactly the callMethodStdBridge shape" phrasing on the list-valued-arg test; it now describes it as a list-valued argument containing a bstr (the shape of that 3rd arg), not the bridge's per-element iteration.

Comment-only amend; tests and behavior unchanged.