v12.1.0

• Updated bundled libfmt to v12.2.0.
• Fixed append-mode RotatingFileSink recovery for base filenames without an extension, so DateAndTime rotated files such as application.20260622_120000 are counted towards max_backup_files instead of accumulating across restarts. (#938)
• Fixed Windows builds that include <windows.h> before Quill wide-string logging headers. (#941)
• Fixed size-based RotatingFileSink rotation after an externally deleted active file is reopened. (#945)
• Fixed bounded queue writes after the reader drains the queue without crossing the reader-position publish batch. (#946)
• Fixed %s timestamp formatting in GmtTime mode on non-UTC machines. (#947)
• Fixed a huge page mapping leak on Linux where munmap failed with EINVAL on queue destruction. Allocations now request MAP_HUGE_2MB explicitly and round the mapping size up to a 2 MiB multiple.
• Fixed the transit event buffer expanding to twice the configured transit_events_hard_limit.
• Backend::start() now throws on the caller thread when transit_events_soft_limit or transit_events_hard_limit is misconfigured, instead of terminating the process from the backend thread.
• Fixed BackendTscClock calls overlapping Backend::stop(). Backend restarts now reconfigure and republish one stable clock allocation, so a conversion already in progress can safely finish without unbounded retained clocks.
• Fixed potential queue corruption when logging std::error_code with locale-dependent or user-provided error categories. The category name and message are now snapshotted once and reused for encoding.
• Fixed RotatingJsonFileSink replaying a stale json payload after a failed size-based rotation.
• Literal { and } in format_pattern are now escaped, while existing doubled-brace spelling remains compatible. Invalid attribute format specifications are rejected during formatter construction.
• timestamp_pattern now rejects the time-of-day-embedding modifiers %c, %Ec, %EX, %OH, %OI, %OM and
  %OS, like %X, which silently froze at a cached value.
• Fixed logging of std::pair, std::tuple and std::array with const-qualified element types, most notably dereferenced std::map iterators (std::pair<Key const, T>), which previously failed to compile.
• The backend singleton lock file is now opened with O_CLOEXEC and O_NOFOLLOW.
• The std::filesystem::path codec now reads the path via native(), avoiding two temporary string allocations on the hot path.
• Codec<std::tuple> now fails with a clear static_assert when the decoded tuple is not formattable. A custom formatter for the complete tuple remains supported even when elements have no standalone formatter.
• TransitEventBuffer expansion now moves the existing events instead of default-constructing and discarding a FormatBuffer allocation for every slot.
• Fixed a C++ data race in BackendTscClock snapshot reads when resynchronization reused a slot concurrently.
• Fixed SIGTERM and SIGINT handling when the backend is running without a valid logger.
• Unbounded queue maximum capacities are now rounded up to the next power of two and validated against the initial capacity.
• Sink exceptions no longer prevent later sinks from receiving the same log or metric event.
• Logging macros now evaluate logger and runtime log-level expressions once per invocation.
• CPU-affinity failures are now reported on macOS, FreeBSD, and NetBSD instead of being silently ignored.
• Minutely and hourly rotation boundaries now stay wall-clock aligned after a late-triggered rotation, instead of permanently drifting off the initial rotation time point.
• Fixed a number of minor bugs and hardened edge cases across the frontend, backend, sinks and codecs, including transactional startup rotation recovery and console colour handling around trailing newlines.
• Clarified the custom-codec exception contract: sizing may throw before reservation, while encoding and decoding must not.
• Documented the QUILL_LOG_LEVEL environment variable. It is now validated during first logger creation; invalid values (including backtrace) throw QuillError, do not register a partial logger, and can be retried.
• create_or_get_sink<TSink>() now throws when a sink with the same name already exists with an incompatible type (in builds with RTTI), instead of returning it for an undefined-behaviour cast.
• Documented that CsvWriter writes fields verbatim and added an opt-in quill::utility::csv_escape_field() helper for RFC 4180 escaping of fields containing commas, quotes or line breaks.
• Backend callback logging no longer self-deadlocks when its own blocking queue is full; additional backend-thread records are dropped instead.
• Exceptions from custom sink periodic tasks are now reported through error_notifier instead of terminating the process.
• Concurrent Backend::stop() callers now wait for the in-progress shutdown to complete before returning.
• Default JSON sinks now suffix named arguments that collide with built-in JSON fields, avoiding duplicate object keys.
• Oversized runtime source paths are now truncated safely instead of overflowing metadata offsets.
• Negative backend and file-sync intervals are now rejected during configuration.
• Fixed Windows std::filesystem::path decoding when byte-packed arguments are not aligned for wchar_t.
• Fixed rotating CsvWriter header writes on Windows after failed rotation recovery, so the header is appended instead of overwriting the beginning of the active CSV file.