Mirrors the vLLM-side rewrite. AppendImage is gone; images now
ride along on Generate via a parallel `images` list.
- Productionize `qwen3_image_token_count` (was test-only). Image
leaf computes its IMAGE_PAD count eagerly at construction from
height/width; `token_count` is no longer "0 until the server
tells us."
- WireChunk shrinks to a single `Tokens(Vec<u32>)` variant — vision
blocks live inline in the token stream.
- `wire_chunks` now returns `(Vec<WireChunk>, Vec<WireImage>)`.
`WireImage` carries `pad_start` / `pad_end` (absolute positions
in the full walk) alongside bytes + mime.
- `assemble_prompt` returns `(chunks, images, match_upto)`.
- `stream_session_mm` / `run_session_generate` take the parallel
images list, filter to those past `match_upto`, and pass them
in `GenerateRequest.images` as `pb::ImageAttachment` entries.
- Drop `SessionHandle::append_image`,
`ContextState::commit_image_token_counts`,
`StreamToken::ImageAppended`, the WireChunk::Image branch in
`learn.rs`, and the now-empty `prompt_to_chunks` helper.
- Add 'v' toggle on the conscious-screen tree to render token-id
vectors in place of text content (debug-aid: lets us see what
the server actually has when output is suspicious).
- Comment out the subconscious-trigger spawn loop — Kent had this
disabled before; it had crept back into running.
Co-Authored-By: Proof of Concept <poc@bcachefs.org>
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