When a model emits an inline <think>...</think> block but the opening
tag is dropped upstream (thinking-mode toggle, truncated stream, or
incomplete upstream filtering), the bare </think> close tag leaked
through to the user in the live progressive edit. The agent-side final
scrubber (agent/think_scrubber.py) already had _strip_orphan_close_tags;
this ports the same logic into GatewayStreamConsumer so the streaming
display stays clean too.
- _filter_and_accumulate: strip orphan close tags before appending the
'no-opening-tag' branch text to _accumulated.
- _flush_think_buffer: same on stream end for held-back partials.
- 14 regression tests (TestStripOrphanCloseTags): all 6 close-tag
variants, multi-tag, partial-tag-untouched, trailing whitespace,
and end-to-end through _filter_and_accumulate / _flush_think_buffer.
Only strips KNOWN close-tag names (case-insensitive) — never arbitrary
tag-shaped substrings — so comparison operators and unrelated prose are
preserved.
Salvaged from PR #43192 by @testingbuddies24.
e07768a53f