[schloerke]

Stacked on #2559. Updates the memory bank so contributor docs describe the async concurrency stack (#2549, #2545, #2546, #2520, #2547, #2548, #2525, #2552, #2559) instead of the global reactive.lock() model it replaces.

Changes

• reactiveInternals.md: the flush loop and lock sections are replaced. New sections cover rounds (request_round() via call_soon in a fresh context, non-waiting starts, rerun instead of nesting), cycles and the busy count, run_once_when_idle(), reactive.flush() / run_until_idle() semantics, async calcs and effects interleaving, destroy-time cancellation, and the deprecated no-op reactive.lock(). Pitfalls are rewritten.
• sessionMessaging.md: the message loop holds no lock. update messages go through run_once_when_idle(), and dispatch messages run as their own tasks. "The flush cycle" becomes "Cycles and the output flush": one message per cycle, sent even when empty; queues reset before the send is awaited; the "recalculating" yield (fix(session): Send each output's progress message before it renders #2525); and the per-task output-name ContextVar (fix(session): Track the rendering output per task for clientdata.output_*() #2559). The session-end section and pitfalls are updated.
• otel.md: reactive_update is a per-session cycle span. It starts when the busy count goes 0→1, and it ends at idle or at session end. The doc covers its parents and children, the start_otel_span() / use_otel_span() helpers, and how test_otel_reactive_update.py tests it.
• bookmarking.md: a new "Restore gate" section (fix(bookmark): Run async on_restore callbacks before the session's effects #2548), and the callback timing now refers to cycles instead of flushes.
• ciAndTooling.md: the playwright-windows job and PR-checks gate, PLAYWRIGHT_INSTALL_ARGS, the pytest.ini timeout and --strict-markers settings, and why -p no:rerunfailures silently drops tests.
• playwrightTesting.md: the Windows-specific tests, how the busy-indicator timing test works, and the async/ and express-session-start test changes.
• New concurrencyTesting.md: how to write tests in the style of test_concurrency.py. It covers the Client drivers, wait_until with its 10 s limit, asyncio.Events instead of sleep durations for ordering, state waits plus settle() for negative assertions, duck-typed session mocks, MockTime, and releasing tasks stranded on dead event loops. architecture.md links to it.

Review notes

Writing these docs turned up a few code leftovers. This PR doesn't change any of them:

• A comment in invalidate_later() still says the round's reactive_update span has no parent. That span now belongs to the session's cycle.
• Shiny no longer calls detached_otel_context() (shiny/otel/_core.py), so it could be removed.
• uploadEnd sets its input in the middle of a cycle instead of through run_once_when_idle(), unlike update messages. This matches R. The docs list it as a pitfall.

Verification

• Each claim was checked against the code on this branch.
• Every file.md#anchor link in memory-bank/ resolves.