Empty intermediate SSE fix

[mzegla]

No description provided.

[Copilot]

Pull request overview

This PR targets a streaming edge case where the final “finish-only” flush can lead to an extra/empty intermediate SSE iteration by propagating an isLast flag from OVMSTextStreamer through servable callbacks into DeltaChannel.

Changes:

• Extend OVMSTextStreamer::Callback to include an isLast boolean derived from finish_reason != NONE.
• Extend DeltaChannel::push() to accept isLast and (currently) mark the channel complete when isLast=true.
• Update GenAI + legacy LM/VLM servables to forward isLast through their streamer callbacks.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/llm/visual_language_model/legacy/servable.cpp	Updates legacy VLM callbacks to forward isLast into the delta channel / unary accumulator.
src/llm/servable.hpp	Updates DeltaChannel::push() signature and completion behavior when pushing the last delta.
src/llm/servable.cpp	Updates base GenAI streaming callback signature to accept/forward isLast.
src/llm/ovms_text_streamer.hpp	Updates OVMSTextStreamer::Callback typedef and documents isLast.
src/llm/ovms_text_streamer.cpp	Computes isLast from finish_reason and forwards it to the callback, including finish-only flush handling.
src/llm/language_model/legacy/servable.cpp	Updates legacy LM streaming callback signature and forwards isLast into the delta channel.

Comments suppressed due to low confidence (1)

src/llm/visual_language_model/legacy/servable.cpp:162

• The streamer callback can receive finish-only deltas (no "delta" object). In that case, rapidjson::Document may be empty/non-object, and calling HasMember() directly can trigger RapidJSON assertions/UB. Guard on delta.IsObject() before HasMember() so the unary VLM path safely ignores finish-only documents.

        auto unaryCallback = [& ctx = *legacyExecutionContext](rapidjson::Document delta, bool /*isLast*/) -> ov::genai::StreamingStatus {
            if (delta.HasMember("delta") && delta["delta"].IsObject() &&
                delta["delta"].HasMember("content") && delta["delta"]["content"].IsString()) {
                ctx.accumulatedUnaryText += delta["delta"]["content"].GetString();
            }