`splitReasoning()` strips paired `<think>…</think>` blocks first, then runs
an unclosed-trailing regex to catch reasoning that hasn't yet streamed its
closer. That second regex was unanchored and greedy:
new RegExp(`<${tag}>([\\s\\S]*)$`, 'i')
So any literal `<think>` somewhere in prose — a model quoting the tag, a
code example, or a stream-mid-tag before the closer arrives — consumed
every paragraph after it to EOF. User-visible symptom: "TUI eats last
paragraph of output," both during streaming and on settled turns.
Real reasoning streams always lead the message (that's the only place an
unclosed opener can legitimately appear during streaming). Anchor the
regex to `^\s*` so mid-prose mentions of the tag are preserved.
Empirical repro before the fix:
splitReasoning('final answer paragraph one.\n\n<think>internal note\n\nfinal answer paragraph two.')
→ text: 'final answer paragraph one.' ← paragraph two GONE
After:
→ text: 'final answer paragraph one.\n\n<think>internal note\n\nfinal answer paragraph two.'
Updated the existing trailing-unclosed test to lead with `<think>` (the
real-world shape) and added a regression test pinning the mid-text case.
ui-tui type-check clean, 808/808 vitest pass.
Models that emit reasoning inline as <think>/<reasoning>/<thinking>/<thought>/
<REASONING_SCRATCHPAD> tags in the content field (rather than a separate API
reasoning channel) had the raw tags + inner content shown twice: once as body
text with literal <think> markers, and again in the thinking panel when the
reasoning field was populated.
Port v1's tag set to lib/reasoning.ts with a splitReasoning(text) helper that
returns { reasoning, text }. Applied in three spots:
- scheduleStreaming: strips tags from the live streaming view so the user
never sees <think> mid-turn.
- flushStreamingSegment: when a tool interrupts assistant output mid-turn,
the saved segment is the stripped text; extracted reasoning promotes to
reasoningText if the API channel hasn't already populated it.
- recordMessageComplete: final message text is split, extracted reasoning
merges with any existing reasoning (API channel wins on conflicts so we
don't double-count when both are present).
