…rs (#10225)

* fix(reasoning): stop prefilled <think> from swallowing tag-less answers

When a chat template injects the thinking start token into the prompt (so
DetectThinkingStartToken returns e.g. "<think>"), the model's output begins
inside a reasoning block and carries only the closing tag. The non-jinja
autoparser fallback (peg-native "pure content" mode, issue #9985) prepends the
start token so the extractor can pair it with the model's </think>.

But on a COMPLETE response that contains no closing tag, the model answered
directly with no reasoning at all. Prepending the start token there manufactures
an unclosed block that swallows the entire answer into reasoning, leaving the
OpenAI `content` field empty. This breaks short/direct answers — session names,
JSON summaries, any terse completion where the model skips the think block —
which come back with empty content. Regression surfaced by #9991, which added
the defensive prefill extraction to the complete-response paths.

Add reasoning.ExtractReasoningComplete: it only honors a prefilled start token
when the response actually contains the matching closing tag (proof a reasoning
block exists). Genuine reasoning tags already in the content still extract;
tag-less content stays content. Apply it at every complete-response site
(applyAutoparserOverride, realtime, openresponses). The streaming per-token
extractor is intentionally left on ExtractReasoningWithConfig — mid-stream an
as-yet-unclosed block is legitimate and must surface as reasoning deltas.

Also adds reasoning.ClosingTokenForStart and hoists the default reasoning tag
pairs to package scope so both helpers share one source of truth.

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* test(reasoning): cover the enable_thinking=false non-thinking-mode regression

Adds the end-to-end case that actually broke session summaries / auto-titles
and was not covered before: a request with enable_thinking=false against a
<think>-capable model. In non-thinking mode the model emits no reasoning block,
so llama.cpp's autoparser returns ChatDeltas with content set and
reasoning_content empty (verified against stock llama-server: same model with
chat_template_kwargs.enable_thinking=false returns reasoning_content=null,
content="hello"). thinkingStartToken is still "<think>" because it is detected
per-model from the enable_thinking=true render, so the old code prepended it and
swallowed the answer. The test fails without the ExtractReasoningComplete gate.

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: Ettore Di Giacinto <mudler@localai.io>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>