Qwen3-1.7B pretty-prints its JSON: it opens the object and writes three
newlines before the first key. escapeRawControls rewrote those structural
newlines into a literal backslash-n, which is legal nowhere outside a string,
so the object stopped parsing and came back as errBrokenJSON.
The comment claimed escaping unconditionally could not turn valid JSON into
anything else, on the grounds that JSON permits no control character outside a
string. It permits three: newline, tab and return are whitespace between
tokens, and that is what pretty-printing is made of.
Measured on the talk fixture against the resident model: 31 of 36 conversational
cases were failing generations and answered from the stub. Every chat reply and
every knowledge answer the resident model wrote was being discarded. Now 25/36
pass every check, 0 errors, and the 15 nudges stay at 15/15.
Sixty of the failures in the 2026-08-05 temperature sweep were one error,
`phraser: model output starts as JSON but does not parse`, all of them in the
reply family and two of them in all twelve runs. The write-up read that as
truncation. It is not: no run hit the token cap.
The string rule in both grammars was `[^"\\]`, which admits a literal
newline. A model that wants two lines writes one, the generation satisfies the
grammar, and json.Unmarshal then rejects it with "invalid character '\n' in
string literal". The object starts with "{", so it came back as errBrokenJSON
and the reply was an empty string. The router's rule also admitted `"\\" .`,
so \q satisfied it and failed to parse the same way.
Both string rules are now llama.cpp's own json.gbnf class: the control range is
out and the escape alternatives are exact. Verified against the resident model
on 8899 — llama-server accepts both grammars and both still emit what they did.
escapeRawControls is the second line, for NoGrammar and for a remote server that
ignores a grammar: a reply whose only fault is a raw newline is readable, so it
is read rather than dropped.
Two bugs, one symptom. A run of the talk eval produced replies that were
literally "{" and "{\n \"" — those strings went out as things Maven said.
First bug: the parser could not tell "the model answered in plain prose"
from "the model started a JSON object and got cut off". Both came back as
empty, and every caller then shipped the raw text. Now an unfinished object
returns an error and each caller uses its own fallback instead. Bare prose
with no JSON in it still passes through, because small models do sometimes
answer that way and the reply is fine.
Second bug, and the actual cause: the grammar capped the response field at
400 characters. I measured it against Qwen3.5-0.8B at three different token
caps — 256, 768 and 2048 — and the reply came back exactly 400 characters
every time, cut mid-word. So the token limit was never what stopped it.
The bound is 1000 now, about six Russian sentences, still low enough to cut
off a repetition loop.
Token caps go from 256 to 768 on the chat and query paths so 1000
characters of Russian actually fits. The nudge path keeps its own cap; a
nudge is meant to be one sentence.
Note: cmd/mavend/replier_llm.go has its own copy of this parser with the
same bug. Left alone here so this commit stays small — that duplicate is
Vikunja #396.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CGeSZxh1DCtRxmFVSYVGvJ
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