perf(chat): batch live thinking rendering and bound timer updates (#5931)

* perf(chat): batch live thinking DOM updates

* test(chat): cover live thinking scheduler lifecycle

* fix(chat): guard background stop-state, restore live thinking text, drop source-text tests

- _closeOpenThinkingMarkup no longer overwrites currentAccumulated for
  backgrounded streams. It now mirrors the guard the delta path already uses
  (`if (!_isBg) currentAccumulated = accumulated`). Without it a backgrounded
  stream's text is written into the foreground session's stop-state, which
  abortCurrentRequest and detachCurrentStream then put in the wrong bubble.

- Split _extractLiveThinkingText into _liveThinkingText (strip every think tag)
  and _closedThinkingText (via extractThinkingBlocks). Slicing from the first
  <think> to the first </think> pinned the live box to "The" for the rest of the
  stream on the `<think>The</think>` + untagged-thinking pattern that the
  hasUnclosedThink detection deliberately keeps streaming through.

- The background transition now flushes with rich:true, so a stream that
  backgrounds mid-thinking isn't left as pre-wrap plain text permanently.

- Move the throttle to static/js/liveThinkingThrottle.js and import it. The
  .mjs suite imports the module instead of slicing it out of chat.js with
  vm.runInNewContext and marker comments.

- Replace the source-text assertions in tests/test_live_thinking_scheduler_js.py
  with behavioral coverage, per tests/TESTING_STANDARD.md. The .mjs suite grows
  from 3 to 6 cases.

- Collapse the duplicated tool_start/agent_step finalizers into one
  _endLiveThinkingSection().

* fix(chat): hoist thinking teardown out of the try block so catch can reach it

In an ES module a function declared inside `try { }` is scoped to that block,
and `catch` is a sibling scope rather than a nested one. _closeOpenThinkingMarkup
was declared inside the try and called from catch, so the call threw
ReferenceError and killed the rest of the error path: the stream never
finalized and the thinking block was never torn down.

Declare _closeOpenThinkingMarkup and a new _endThinkingOnTerminalPath next to
the existing _flushLiveThinking / _cancelLiveThinkingWork outer lets and assign
them inside the try, which is the pattern those two already use for exactly
this reason.

Verified against a live stream in a browser: before, clicking stop mid-thinking
logged "_closeOpenThinkingMarkup is not defined" and left no finalized thinking
section; after, the block collapses to "View thinking process" correctly.

* perf(chat): extract live thinking at commit cadence

* fix(chat): bound live thinking work

* test(chat): update stream invariant assertions

---------

Co-authored-by: Léo <leograndcontact@gmail.com>

tests/test_live_thinking_chat_integration.py

@@ -0,0 +1,145 @@
+"""Source-level wiring guards for live-thinking stream lifecycle.
+
+The pure scheduler suite covers timing behavior. These assertions pin the
+browser-only integration seams that are impractical to import without the full
+application DOM.
+"""
+
+from pathlib import Path
+
+
+_CHAT = (Path(__file__).resolve().parent.parent / "static" / "js" / "chat.js").read_text(
+    encoding="utf-8"
+)
+
+
+def _between(start: str, end: str) -> str:
+    return _CHAT.split(start, 1)[1].split(end, 1)[0]
+
+
+def test_in_thinking_delta_short_circuits_before_cumulative_normalization():
+    delta_handler = _between(
+        "let _delta = json.delta;",
+        "} else if (json.type === 'research_progress')",
+    )
+    delta_path = _between(
+        "// Detect thinking-in-progress:",
+        "} else if (json.type === 'research_progress')",
+    )
+    guard = "if (!_thinkingAnalysisGate.shouldAnalyze(roundText, {"
+    normalize = "markdownModule.normalizeThinkingMarkup(roundText)"
+    assert guard in delta_path
+    assert delta_path.index(guard) < delta_path.index(normalize)
+    assert "_queueLiveThinking(roundText);" in delta_path
+    assert "createThinkingAnalysisGate" in _CHAT
+    projector_append = "_roundDisplayProjector.append(_delta, roundText);"
+    assert projector_append in delta_handler
+    assert delta_handler.index(projector_append) < delta_handler.index(guard)
+    assert "_renderStream({ knownNormal: true, displayText: _roundDisplayProjector.current() });" in delta_path
+    assert "_replyDisplayProjector.append(_delta, roundReplyText)" in delta_path
+
+
+def test_short_close_grace_expires_without_another_delta():
+    assert "function _scheduleThinkingGrace()" in _CHAT
+    grace = _between(
+        "function _scheduleThinkingGrace()",
+        "function _replyAfterClosedThinking",
+    )
+    assert "setTimeout(() =>" in grace
+    assert "_finishLiveThinkingTransition();" in grace
+    cancel = _between("_cancelLiveThinkingWork = () =>", "function _finalizeLiveThinking")
+    assert "_cancelThinkingGrace();" in cancel
+    delta_path = _between(
+        "// Detect thinking-in-progress:",
+        "} else if (json.type === 'research_progress')",
+    )
+    false_close = _between(
+        "// Detect false close:",
+        "if (hasUnclosedThink && !isThinking)",
+    )
+    assert "Do NOT require a prior unclosed delta" in false_close
+    assert "_afterClose &&" in false_close
+    assert "&& isThinking" not in false_close.split("let _falseCloseDeadline", 1)[1].split("if (isThinking)", 1)[0]
+    assert "_thinkingRecheckAt = _falseCloseDeadline || 0;" in delta_path
+
+
+def test_terminal_paths_use_one_authoritative_rich_round_render():
+    tool_path = _between(
+        "} else if (json.type === 'tool_start') {",
+        "} else if (json.type === 'tool_output') {",
+    )
+    assert "_endLiveThinkingSection({ rich: false });" in tool_path
+    assert tool_path.count("_finalizeRoundRender();") == 1
+    assert "_renderStream();" not in tool_path
+
+    agent_path = _between(
+        "} else if (json.type === 'agent_step') {",
+        "} else if (json.type === 'budget_exceeded') {",
+    )
+    assert "_endLiveThinkingSection({ rich: false });" in agent_path
+    assert agent_path.count("_finalizeRoundRender();") == 1
+    assert "if (!roundFinalized)" not in agent_path
+
+    catch_path = _between(
+        "// foreground session's text.\n      const _isBgCatch",
+        "} finally {",
+    )
+    assert "if (_isBgCatch)" in catch_path
+    assert "_cancelLiveThinkingWork();" in catch_path
+    assert "_catchTerminalView = _finalizeInterruptedView();" in catch_path
+    assert "_finalizeRoundRender();" not in catch_path
+    assert "_endThinkingOnTerminalPath({ rich: false });" in catch_path
+    assert "const _catchViewHolder = _catchTerminalView?.holder || holder;" in catch_path
+
+    round_finalizer = _between(
+        "_finalizeRoundRender = () => {",
+        "_finalizeInterruptedView = () => {",
+    )
+    assert "if (roundFinalized) return roundFinalization;" in round_finalizer
+    assert round_finalizer.index("processWithThinking") < round_finalizer.rindex("roundFinalized = true;")
+    assert "lastContentRoundHolder = terminalHolder;" in round_finalizer
+
+    interrupted_finalizer = _between(
+        "_finalizeInterruptedView = () => {",
+        "function _replyAfterClosedThinking",
+    )
+    assert "finalization?.hasContent" in interrupted_finalizer
+    assert "lastContentRoundHolder || finalization?.holder" in interrupted_finalizer
+
+    stop_path = _between(
+        "// Render whatever was accumulated so far",
+        "// Reset button state",
+    )
+    assert "const _stoppedViewHolder = _terminalView?.holder || currentHolder;" in stop_path
+    assert "_stoppedViewHolder.querySelector('.body').appendChild(stoppedIndicator);" in stop_path
+
+    done_path = _between(
+        "if (data === '[DONE]') {",
+        "try {\n              const json = JSON.parse(data);",
+    )
+    assert "_finalizeLiveThinking(_closedThinkingText(roundText), false);" in done_path
+    assert "_renderStream();" not in done_path
+
+    post_loop = _between(
+        "if (!_streamSawDone) {",
+        "// --- Final render (skip if stream was ever backgrounded or currently in background) ---",
+    )
+    assert "_cancelLiveThinkingWork();" in post_loop
+    assert "_renderStream();" not in post_loop
+
+    recovery_path = _between(
+        "function _tryAutoRecover(holder, accumulated, sessionId)",
+        "function _removeStallBanner()",
+    )
+    assert "processWithThinking" not in recovery_path
+
+
+def test_detach_synchronously_cancels_delayed_view_work():
+    registration = _between("_activeStreams.set(streamSessionId", "_syncForegroundStreamGlobals();")
+    assert "cancelViewWork: () => _cancelLiveThinkingWork()" in registration
+
+    detach = _between("export function detachCurrentStream", "// _notifyStreamComplete")
+    cancel = "if (active.cancelViewWork) active.cancelViewWork();"
+    background = "_backgroundStreams.set(sessionId"
+    assert cancel in detach
+    assert detach.index(cancel) < detach.index(background)