`strip_think` removes a dangling (unclosed) `<think>` block via
`_THINK_OPEN_RE`, but that pattern was anchored to the start of the string
(`^\s*<think>`). An unclosed `<think>` (or `<thinking>`) opener that
appears *after* any leading output was therefore only half-handled: the
stray tag itself was removed by `_THINK_TAG_RE`, but the reasoning content
following it leaked straight to the user.
strip_think("Hello! <think> I am thinking.") # -> "Hello! I am thinking." (leak)
strip_think("Sure.\n<think>\nLet me reconsider...") # -> leaks the reasoning
`strip_think` feeds user-facing output across research, email replies,
notes, and scheduled tasks, so this leaks chain-of-thought to end users.
Un-anchor `_THINK_OPEN_RE` so a dangling opener anywhere strips from the
opener to end of string, consistent with the existing start-of-string
behavior. Content before the opener, closed `<think>...</think>` blocks,
and tag-free text are all preserved.
tests/test_strip_think.py covers the mid-text leak (fails before this
change), start-anchored unclosed, closed blocks, no-tag passthrough,
content-before-opener, and mixed closed+unclosed. Full existing think
suite still passes.
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