froggeric

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Qwen-Fixed-Chat-Templates

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Problem

The v19 changelog states preserve_thinking defaults to true ("mathematically guaranteeing 100% KV Cache prefix matching out-of-the-box", curing "amnesia stalls"). The v20 rewrite regressed this:

{%- set _preserve_thinking = preserve_thinking if preserve_thinking is defined else false %}

v19's actual logic was preserve-unless-explicitly-disabled (preserve_thinking is defined and preserve_thinking == false → strip). No inference engine passes this kwarg by default, so v20 users silently get false: past <think> blocks are stripped as last_query_index advances each turn, mutating already-rendered history and invalidating the KV cache prefix every single turn — exactly the problem described in Discussion #1.

Fix

One word: else false → else true, restoring the documented v19 behavior. Users who want stripping can still pass preserve_thinking: false.

Each fix in this series is an independent PR based on current main (v20); they touch overlapping regions of the same file, so merging one may require the others to be rebased — happy to update them.