fix(local-model): rollback copies follow each tag's own draft length

The previous commit counted 4 rollback copies of the recurrent state for every GGUF with a
prediction layer, the runtime's default `draft_num_predict`. A tag can set its own in its
params layer, and the runtime then passes that as `--spec-draft-n-max`, which is what
`need_n_rs_seq()` turns into rollback copies. Read on 2026-11-08:

- qwen3.6:35b-a3b-mtp-q4_k_m: draft_num_predict 2, so 2 copies (was counted as 4).
- qwen3.8:27b-mtp-q4_k_m: draft_num_predict 4.
- qwen3.8:27b-q8_0: none in its params, so the runtime's 4.

The 35B-A3B GGUF row's overhead drops by 132 MB: 0.971 instead of 0.976 on a 36 GB M3 Pro or
M3 Max, the same pick. test/local-model-catalog.test.ts now carries the drafted tokens per row
instead of a yes/no prediction layer.

Also states what was verified about llama.cpp's checkpoint default: 8 from b6800 to b8200,
32 from b8250 together with a checkpoint every 8,192 prompt tokens (common/common.h at those
tags), in place of an inferred reason. Checked in the b12111 source as well: the draft context
of a Qwen-family MTP model caches the prediction block alone (`mtp_on_hybrid_qwen`, layers at
or above n_layer()), and the main context leaves it out, so the row counts that layer once.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/local-model/runtime.ts

@@ -40,13 +40,13 @@
  *       of the catalogue's `llamacpp` rows: a checkpoint is a host copy of the state that
  *       cannot be rolled back (the recurrent state of the linear-attention layers, or the
  *       sliding-window cache), two or three per request, and llama-server keeps up to 32 by
- *       default. 32 copies of the 27B's 157 MB state are 5 GB that the session holds for
- *       nothing: an agent's next request restores the newest checkpoint of the previous one.
- *       8 (llama.cpp's own default before it went to 32 to cover a 262,144-token window in
- *       8,192-token steps) keeps the last few requests. The cost: a prompt that differs from
- *       the last checkpoints further back (a compaction, a cleared old tool result) is
- *       processed again from the newest checkpoint before that point, or from its start.
- *       8 checkpoints are counted in every `llamacpp` row's `overheadBytes`.
+ *       default. 32 copies of the 27B's 157 MB state are 5 GB, most of which an agent never
+ *       uses: its next request restores the newest checkpoint of the previous one. 8
+ *       (llama.cpp's own default from b6800 to b8200; it became 32 at b8250, together with a
+ *       checkpoint every 8,192 tokens of a long prompt) keeps the last few requests. The cost:
+ *       a prompt that differs from the last checkpoints further back (a compaction, a cleared
+ *       old tool result) is processed again from the newest checkpoint before that point, or
+ *       from its start. 8 checkpoints are counted in every `llamacpp` row's `overheadBytes`.
  *    The MLX runner reads none of the four (nothing under mlxrunner/ does): an `mlx` row's
  *    figures do not depend on them.
  *  - PORT (`chooseRuntimePort()`). Chosen ONCE by binding, from `RUNTIME_PORT_FIRST` across