rMLX 0.2.4

Vision, KV, and embedding-lookup bug-fix batch for Qwen3-VL and Gemma 4, plus a
/metrics/cache recording/docs fix and a Homebrew bottle build+publish flow.
Highlights: Qwen3-VL large images now work end to end (KV sized from --max-ctx;
the O(seq²) embedding lookup that tripped the Metal GPU watchdog is gone), and
Gemma 4 image grounding is fixed by placing image tokens inside the user turn. No
breaking changes.

Added

• Homebrew bottle build+publish flow. scripts/release/build_bottle.sh +
  make bottle drive brew bottle against an installed keg, rename the local
  bottle to the GitHub-Release asset name, and emit the ready-to-paste
  bottle do block; documented as a release-time step in docs/RELEASING.md.
  The committed formula stays source-build until a real bottle is uploaded, so
  existing tap installs are unaffected. (#143, #139)

Fixed

• /metrics/cache TTFT empty for non-streaming completions. Both
  non-streaming paths (generate_blocking, OpenAI + Anthropic) measured TTFT
  but never pushed it into the in-memory ttft_store ring — only the streaming
  path did, so ttft stayed [] for non-streaming traffic. The ring is now
  written on both paths. docs/SERVER.md is realigned to the endpoint's actual
  shape (models[], itl, tokens_in/out), dropping the never-emitted
  prompt_cache / last_itl keys. (#142, #141)
• Gemma 4 image grounding (degenerate / image-independent output). The
  per-image token block was spliced after BOS but before the user-turn opener,
  leaving the image outside the user message; the model then ignored it. Image
  blocks are now spliced inside the (final) user turn via a shared
  splice_image_block, matching the HF/mlx-vlm placeholder substitution. Fixes
  the reported e4b QAT-fp4 degeneration (the soft tokens were correct all along)
  and a latent flakiness that affected all Gemma 4 image requests; Qwen3-VL is
  unified onto the same path. (#144, #140)
• Qwen3-VL ignored --max-ctx; large images failed with a slice_update
  broadcast. The image and text generate paths built KV with the bare 4096
  default and never bracketed prefill, so any prompt over 4096 tokens (a large
  image tiles to thousands of soft tokens) overran the fixed buffer. Both paths
  now size the KV ring from the effective --max-ctx and chunk the prefill;
  an over-cap prompt returns a clean context_overflow instead of the broadcast
  panic. (#145, #138)
• Qwen3-VL large images hit the Metal GPU watchdog. The quantized embedding
  lookup used an O(seq²) eye(seq) @ w identity-matmul on CPU (plus a GPU↔CPU
  round-trip); embedding the whole augmented prompt for a large image produced a
  single command buffer that overran the ~10 s watchdog. Replaced with on-device
  take + dequantize (O(seq)); added query-tiled ViT attention as a faithful
  defense for very large single images. (#147, #146)
• Qwen3.6 (qwen3_5_moe) embedding lookup carried the same O(seq²)
  eye(seq) @ w-on-CPU trick (plus an unsafe block); ported to the same
  on-device take + dequantize. Numerically faithful, removes a per-step CPU
  round-trip. (#149, #148)

Performance

• Qwen3-VL: large images (e.g. 2560×2560 → 6400 soft tokens) now complete
  end-to-end instead of aborting the process at the Metal GPU watchdog. (#145, #147)

Tested

• New CI-gated tests: image-token placement (in-turn, last-turn, multi-image,
  after-BOS fallback), ViT attention tiling equals a single SDPA, and
  qwen3_5_moe embed_lookup numeric equivalence across both dtype arms (the
  prior coverage was #[ignore] + env-gated). Real-model proofs across Qwen3-VL
  (KV + large-image), Gemma 4 e4b QAT-fp4 vision, and Qwen3.6 (decode-TPS
  same-session A/B: no regression).