This release contains over 160 commits, focusing on the technical debts
cleaning including refactorings, bug fixes, test coverage improvement, and
option cleanups. The release also includes portability improvements per
upstream issues report.

New features:

• Add EXTENT_ALLOC_FLAG_PINNED so custom extent-allocation hooks can
  mark non-reclaimable mappings, such as HugeTLB pages, for preferential
  reuse outside the decay and purge pipeline. Add the mallctl interfaces
  stats.pinned, stats.arenas.<i>.pinned,
  stats.arenas.<i>.extents.<j>.npinned,
  stats.arenas.<i>.extents.<j>.pinned_bytes, and
  stats.arenas.<i>.mutexes.extents_pinned.{counter} to report
  pinned-memory usage and mutex statistics. (@binliu19: be2de8c)
• Allow resuming per-CPU arena selection via thread.arena.
  (@Algunenano: 68c35f6)
• Better align the contents of human-readable and JSON malloc statistics.
  (@spredolac: 68fe1be, 30b1a41, 04aad97)
• Replace the runtime experimental_infallible_new option with the
  compile-time --enable-cxx-infallible-new option, enabling
  compiler-level optimizations and optimization in move constructors,
  and fix the new(std::nothrow) contract (@spredolac: 160ab9d, fe33667)

Incompatible changes:

• Adapt tcache fill and retention targets per bin to demand observed
  between GC events, replacing the fixed refill/flush policy. Remove
  seven legacy non-experimental controls: lg_tcache_nslots_mul,
  tcache_nslots_small_min, tcache_nslots_small_max,
  tcache_nslots_large, tcache_gc_delay_bytes,
  lg_tcache_flush_small_div, and lg_tcache_flush_large_div.
  Corresponding malloc_conf settings are silently ignored, matching
  opt.* mallctls return ENOENT, and tcache_ncached_max remains
  supported. (@spredolac: d13fe91)

Bug fixes:

• Preserve errno across free, free_sized, and free_aligned_sized,
  and across process_madvise-based page purging. (@spredolac: 3a77966,
  86f0582)
• Fix numeric overflow checks in size classes. (@spredolac: 6b24522)
• Accept NULL in free_sized() and free_aligned_sized() (C23
  correctness). (@bigbruno: 7ce8b91)
• Fix TSD lifecycle edge cases by 1) initializing thread-cache bins before
  marking the cache enabled, preventing reentrant bootstrap allocations
  from using uninitialized state, and 2) avoiding TSD recreation for late
  deallocations after thread teardown on generic-TSD platforms.
  (@fzakaria: 54f22c8, @spredolac: fb5499a)
• Use O_CLOEXEC when opening the THP sysfs file in init_thp_state.
  (@ibookstein: d070554)
• Fix duplicate opt.stats_print and opt.stats_print_opts fields in
  malloc_stats_print output. (@spredolac: dfe3a2e)
• Fix a potential deadlock during arena_reset. (@guangli-dai: 6957341)
• Fix a prof-sampling / guard-page interaction bug in the SAN. (@gctony:
  e36a0fa)

Optimizations and refactors:

• Modularize jemalloc's front end by extracting arena management,
  initialization, fork orchestration, and allocation dispatch from
  jemalloc.c; untangle tcache/arena ownership; and consolidate the
  internal header graph to eliminate circular dependencies. (@spredolac:
  ba1e2fe, 8874597, 9d75722, de9ad14, ...)
• Simplify ctl dispatch by refactoring arena helpers, internalizing an
  implementation-only control, replacing control-flow macros with typed
  helpers, and organizing ctl.c by subsystem. (@spredolac: 9e14346,
  901365d, 4e903a0, 5bc8d6e)
• Cap the base-block growth heuristic to avoid virtual-memory exhaustion
  under rare racy conditions. (@guangli-dai: 2f4db8c)
• Move background-thread lifecycle and state operations into the
  background-thread module, clarifying ownership independently of PAC/HPA
  callers. (@guangli-dai: f1f0792)
• Simplify the page-allocation boundary by replacing PAI vtable dispatch
  with direct PAC/HPA calls, removing the obsolete pai_t/pai.h
  abstraction, and moving deferred-work and decay orchestration out of the
  arena. (@guangli-dai: 1dfa6f7, 8edd101, d410f43)
• Refactor statistics collection and rendering into separate
  gather/emission stages and descriptor-driven tables. (@spredolac:
  184f304, 80c8fcb)
• Introduce an OS abstraction layer and move platform-dependent
  file/process I/O, time, synchronization, CPU, virtual-memory, atfork,
  error-handling, profiling, thread-yield, and configuration-access
  operations out of allocator core code. (@guangli-dai: c4158ac,
  c8e2e01, ...)

Portability improvements:

• Replace the std::__throw_bad_alloc call with standard C++ (#2900).
  (@lexprfuncall: 1a15fe3)
• Make arena_s use a flexible array member (bin_t all_bins[]) for C99
  or newer. (@grueninger: 300b58b)
• Fix rdtscp detection with --with-lg-vaddr. (@xinydev: e8a0d2b)
• Fix malloc_getcpu on macOS to read the current CPU number correctly.
  (@Algunenano: 5aabbc8)
• Use CLOCK_MONOTONIC for background-thread sleep to prevent
  clock-rollback stalls, and detect monotonic-condvar support at configure
  time. (@antonio2368: ebacec3, 8361239)
• Fix compilation warnings on macOS. (@gctony: abb0a8a)
• Fix thread-exit TSD cleanup on MinGW builds. (@gctony: 1e92317)
• Fix GCC 16 build warnings by removing -Wpedantic violations in macro
  and function syntax and explicitly NUL-terminating profiling thread-name
  copies to resolve -Wstringop-truncation. (@grueninger: 5acdcee,
  c22d929, @jasonangelov: 6a245e0)
• Parse PID-namespace symlinks without glibc-dependent strtok/atol,
  and return identifiers as uint64_t. (@guangli-dai: 278d90a)