Modelfile: add explicit stop tokens to prevent EOS bleed-through

Without these, Ollama only honored <|im_end|> from the GGUF metadata.
The model occasionally emits <|endoftext|> instead and Ollama kept
generating past it, synthesising a fake new user turn — reproducible
via make smoke.

Adding <|im_end|>, <|endoftext|>, and <|im_start|> as explicit stops
gives clean termination.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

CHANGELOG.md

@@ -7,6 +7,13 @@ and documentation**, not the underlying base model.
 
 ## [Unreleased]
 
+### Fixed
+- `Modelfile`: added explicit `PARAMETER stop` directives for `<|im_end|>`,
+  `<|endoftext|>`, and `<|im_start|>`. Ollama was only picking up
+  `<|im_end|>` from the GGUF metadata, so when the model emitted
+  `<|endoftext|>` it kept generating past it and synthesised a fake new
+  user turn. Reproducible via `make smoke` before/after.
+
 ### Removed
 - `Modelfile.z13` and the `z13` build profile. The Z13-specific tuning
   (Q3_K_S + 8K ctx + FA + q8_0 KV cache) wasn't meaningfully different

Modelfile

@@ -28,6 +28,15 @@ PARAMETER top_k 20
 PARAMETER repeat_penalty 1.05
 PARAMETER num_ctx 16384
 
+# Stop tokens. Without these, Ollama only honors <|im_end|> from the GGUF
+# metadata; the model occasionally emits <|endoftext|> instead and Ollama
+# keeps generating past it (synthesising a fake new user turn). Listing
+# both — plus <|im_start|> as a belt-and-braces guard against the same
+# loop — keeps responses cleanly terminated.
+PARAMETER stop "<|im_end|>"
+PARAMETER stop "<|endoftext|>"
+PARAMETER stop "<|im_start|>"
+
 SYSTEM """You are Janus, a precise and capable assistant for reasoning, writing, coding, and long-form dialogue.
 
 Behavior rules: