[AdirAmsalem]

Description

Registers lucy-2.6, the successor to lucy-2.5, on the realtime surface. It mirrors the JS SDK registry, the source of truth that this package's tests are written against. The model is already served in production; this PR only makes it reachable through the typed SDK surface.

1. lucy-2.6 is opt-in by explicit name. lucy-latest still resolves to lucy-2.5; flipping the alias is a follow-up. The alias entry, its comments, geometry and speeds are untouched.
2. 2.6 offers the fast tier on realtime. The API serves it on ?speed=fast and bills it like 2.5, so the entry advertises Speed::Fast and 2.6 joins the fast-mode model lists.
3. lucy-2.5 is unchanged. This change is purely additive.

Geometry was confirmed against the deployed model config: 1280x720 at 30 fps for realtime, a field-for-field clone of lucy-2.5's realtime entry. This SDK is realtime-only, so there is no batch entry.

Usage

decart::ConnectOptions options;
options.model = decart::models::realtime("lucy-2.6");
// urlPath "/v1/stream", 1280x720 @ 30fps, supportedSpeeds {Speed::Fast}
options.speed = decart::Speed::Fast;  // optional fast mode (2x rate, US only)

Changes

File	Change
src/models.cpp	kRealtime entry {"lucy-2.6", 30, 1280, 720, true, /*fastSpeed=*/true} right after lucy-2.5, and the std::array<Entry, N> size literal goes from 8 to 9
include/decart/models.h	"lucy-2.6" added to the list of canonical names in the realtime() doc comment
include/decart/realtime/types.h, include/decart/realtime/realtime.h, README.md, examples/realtime_warmup.cpp	fast-mode model lists now include lucy-2.6
tests/test_models.cpp	field-by-field block for 2.6 (name, /v1/stream, 30 fps, 1280x720, supportedSpeeds == {Fast}); 2.6 added to the explicit fast checks and the withFast set; canonicalOnly count goes from 5 to 6
tests/test_stream_url.cpp	supportsSpeed(lucy-2.6, Fast) positive check

No version bump.

Verification

Linux (Amazon Linux 2023) / GCC 11.5 / CMake 3.22 / Ninja:

Command	Result
./scripts/format.sh --check (clang-format 15.0.7)	clean
cmake --preset release -DDECART_LIVEKIT_VERSION=1.11.0 + cmake --build --preset release -- -k 0	every source file compiles, including the realtime/LiveKit code, realtime_warmup.cpp, test_models.cpp and test_stream_url.cpp. All 5 executables fail to link locally (4 examples + decart_tests): the prebuilt LiveKit 1.11.0 Linux binaries require glibc 2.38 and a newer libstdc++ (GLIBCXX_3.4.30), and this VM has glibc 2.34. This is a limit of the VM, unrelated to this change. CI on ubuntu-latest/macOS/Windows is the authoritative full-build check.
cmake -B build/norealtime -S . -G Ninja -DCMAKE_BUILD_TYPE=Release -DDECART_BUILD_REALTIME=OFF -DDECART_BUILD_TESTS=ON -DDECART_BUILD_EXAMPLES=ON + cmake --build build/norealtime	builds
ctest --test-dir build/norealtime --output-on-failure	1/1 passed
./build/norealtime/tests/decart_tests	19 test cases, 112 assertions, 0 failed. This includes all of test_models.cpp and test_stream_url.cpp; only test_messages.cpp (realtime-only, untouched here, no model names) is excluded in this config.
Same tests with only the lucy-2.6 registry line removed	4 test cases fail (3 failed assertions, plus one test case that throws ModelNotFound), so the new assertions do pin the change

Compatibility

Additive, and source- and ABI-compatible. kRealtime is a file-local constexpr in an anonymous namespace, so growing it changes no exported symbol, type layout or function signature. Existing model names, including lucy-2.5 and lucy-latest, behave exactly as before.

Follow-ups

• Flip lucy-latest to lucy-2.6 once the server-side alias moves.