Add tokenizer longhaul cache

docs/token-cache.md

@@ -30,3 +30,24 @@ call `llama_token_cache_flush()`.
 
 The 5 GiB limit accounts for logical entry payloads. SQLite metadata and bounded
 journal files are not included.
+
+## Tokenizer longhaul
+
+Qwen3.5 MoE and Laguna models can move their reverse-token and BPE-merge indexes
+into a persistent, disk-backed index while keeping a bounded lookup working set:
+
+```text
+--tokenizer-longhaul
+--tokenizer-longhaul-cache N
+```
+
+`N` is the application-owned lookup cache budget in MiB and is required when
+the mode is enabled. The mode is independent of model `--longhaul`, so the two
+can be used together. The finite tokenizer index builds in the background while
+model loading continues. If tokenizer work arrives first, it waits for atomic
+index publication; build or storage failures are reported instead of silently
+falling back to an unbounded tokenizer.
+
+The persistent index uses the directory selected by `--token-cache-dir` and is
+subject to `--token-cache-size`. Tokenized-text results continue to be cached
+on demand and therefore do not have a finite completion point.