salience: client-side pad expansion, drop AppendImage

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>

src/subconscious/learn.rs

@@ -40,14 +40,15 @@ struct ScoreResult {
     total_logprob: f64,
 }
 
-/// Convert a flat (prompt_tokens, images) pair into the interleaved
-/// chunks the session protocol expects. Tokens up to the next
-/// `<|vision_start|>` become a Tokens chunk; each
-/// `<|vision_start|>..<|vision_end|>` run collapses into one Image
-/// chunk paired by position with the next entry in `images`. The
-/// server re-expands the IMAGE_PADs on AppendImage.
-fn prompt_to_chunks(prompt: &[u32], images: &[WireImage]) -> Vec<WireChunk> {
-    let mut out: Vec<WireChunk> = Vec::new();
+/// Find each <|vision_start|>...<|vision_end|> run in the flat prompt
+/// and pair it with the matching entry in `images`. Returns a list
+/// of `ImageAttachment` with absolute pad-range positions, ready
+/// to drop into `GenerateRequest.images`.
+fn pair_images_to_ranges(
+    prompt: &[u32],
+    images: &[WireImage],
+) -> Vec<pb::ImageAttachment> {
+    let mut out: Vec<pb::ImageAttachment> = Vec::new();
     let mut cur = 0;
     let mut img_idx = 0;
     while cur < prompt.len() {
@@ -60,22 +61,16 @@ fn prompt_to_chunks(prompt: &[u32], images: &[WireImage]) -> Vec<WireChunk> {
             let img = images.get(img_idx)
                 .unwrap_or_else(|| panic!(
                     "image index {} out of range for {} images", img_idx, images.len()));
-            out.push(WireChunk::Image {
+            out.push(pb::ImageAttachment {
                 bytes: img.bytes.clone(),
                 mime: img.mime.clone(),
-                known_expanded_len: (end - cur) as u32,
+                pad_range_start: cur as u32,
+                pad_range_end: end as u32,
             });
             img_idx += 1;
             cur = end;
         } else {
-            let next_vs = prompt[cur..].iter()
-                .position(|&t| t == tokenizer::VISION_START);
-            let end = match next_vs {
-                Some(o) => cur + o,
-                None => prompt.len(),
-            };
-            out.push(WireChunk::Tokens(prompt[cur..end].to_vec()));
-            cur = end;
+            cur += 1;
         }
     }
     out
@@ -95,36 +90,22 @@ async fn call_score(
         return Ok(Vec::new());
     }
 
-    let chunks = prompt_to_chunks(prompt, images);
+    let images_pb = pair_images_to_ranges(prompt, images);
     let mut handle = SessionHandle::open(client).await?;
 
-    // Walk chunks: AppendImage for each image, prefill-only Generate
-    // for each text run between images. Accumulate any trailing text
-    // run into `pending` for the final logprob-generating Generate.
-    let mut pending: Vec<u32> = Vec::new();
-    for chunk in chunks {
-        match chunk {
-            WireChunk::Tokens(t) => pending.extend(t),
-            WireChunk::Image { bytes, mime, .. } => {
-                if !pending.is_empty() {
-                    handle.prefill_only(std::mem::take(&mut pending)).await?;
-                }
-                handle.append_image(bytes, mime, false).await?;
-            }
-        }
-    }
-
     // Final Generate: max_tokens=0 so the server runs prefill of the
-    // trailing `pending` tokens and emits Token events for each
-    // position covered by logprobs_ranges, then Done. logprob_top_k=0
-    // means "just the sampled (prompt) token's logprob" — no top-k
-    // alternatives, which is all call_score historically needed.
+    // full prompt and emits Token events for each position covered
+    // by logprobs_ranges, then Done. logprob_top_k=0 means "just
+    // the sampled (prompt) token's logprob" — no top-k alternatives,
+    // which is all call_score historically needed. Images attach
+    // inline via `images`; the prompt already contains their pre-
+    // expanded vision blocks at the declared ranges.
     let logprobs_ranges: Vec<pb::PositionRange> = ranges.iter()
         .map(|(s, e)| pb::PositionRange { start: *s as u32, end: *e as u32 })
         .collect();
     let req = pb::GenerateRequest {
         session_id: handle.session_id.clone(),
-        append_tokens: pending,
+        append_tokens: prompt.to_vec(),
         offset: handle.committed_len,
         truncating: false,
         max_tokens: 0,
@@ -136,6 +117,7 @@ async fn call_score(
         top_k: 0,
         stop_token_ids: Vec::new(),
         priority: priority.unwrap_or(0),
+        images: images_pb,
     };
 
     let mut stream = handle.generate(req).await?;