@@ -0,0 +1,251 @@
+# Changelog
+
+All notable changes to `rmw_unix_socket_cpp` are documented here.
+
+The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [0.5.0] - 2026-08-27
+
+The wait/wakeup release. The 200 ms `rmw_wait` poll is gone, replaced by an
+event-driven doorbell; TRANSIENT_LOCAL latched replay is rebuilt as a pull from
+a per-publisher shared-memory ring; and the per-node graph guard conditions that
+`rclcpp`'s `GraphListener` actually waits on are finally triggered.
+
+> **Upgrade together.** See [Upgrade notes](#upgrade-notes-050) — a mixed-build
+> fleet can lose latched replay and registry wakeups during the rollout window.
+
+### Added
+
+- **Pull-based TRANSIENT_LOCAL replay** (#60). A latched publisher writes each
+  sample into a per-publisher shm ring (`tl_ring`, `qos.depth` per-record-seqlocked
+  slots) at publish time; a late-joining subscription reads that ring itself
+  inside `rmw_create_subscription`. The idle publisher is never woken, polled, or
+  rung. History is enqueued before the subscription handle returns, so it always
+  precedes live samples. Payloads over `TL_EMBED_CAP` (1 KiB) ride the existing
+  durable segments as 32-byte descriptors; ring bytes are capped at
+  `TL_RING_MAX_BYTES` (2 MiB).
+- **`rmw_subscription_options_t::ignore_local_publications`** (#49). Previously
+  discarded at creation. Each context now draws a random 64-bit `context_id` in
+  `rmw_init` and embeds it in the trailing 8 bytes of every GID, so
+  `is_same_context()` answers from bytes already on the wire — no extra traffic,
+  no wire-format change. "Local" is the same `rmw_context_t`, per the rmw
+  contract, not merely the same process.
+- **Event-driven registry wakeup (doorbell).** Each context binds a doorbell
+  socket at `rmw_init`; every registry mutation sends one octet to every
+  registered doorbell strictly *after* bumping the generation, and `rmw_wait`
+  drains its doorbell strictly *before* reading the generation. That ordering
+  pair makes a lost wakeup impossible. No new threads, no registry layout change.
+- **Graph-change triggering of per-node guard conditions** (#43).
+- CI: **Lyrical** added to the build & test matrix (#17); CI now also runs on
+  `devel` pushes and PRs.
+- GitHub issue forms and a pull request template (#56).
+- Tests: `test_rmw_wait.cpp` (new, +648 lines), `test_shm_transport.cpp` (+283),
+  substantial additions to `test_rmw_qos.cpp` (+873), `test_rmw_graph.cpp`,
+  `test_transport.cpp`, `test_rmw_pub_sub.cpp`, and
+  `test_rmw_service_client.cpp`.
+
+### Changed
+
+- **VOLATILE late joiners no longer receive latched history.** Pulled records
+  are filtered by durability — DDS-correct behaviour. The old push path replayed
+  to every subscriber on the topic regardless of its durability QoS.
+- The `ENTRY_DOORBELL` slot is now registered **lazily**, on the first
+  `rmw_wait` holding a graph guard condition, so only graph-event consumers
+  (`wait_for_service`, `GraphListener`, rosbag2) pay for registry wakeups.
+  Doorbell-slot mutations no longer ring, which removes a K²/2 registration
+  mini-storm.
+- Removed with the push machinery: `transient_local_pubs` (and its mutex),
+  `known_subscriber_paths`, `CachedMessage` / the heap message cache,
+  `transient_local_publish`'s replay loop, and the wait-side TL replay block.
+- `registry`: `teardown_slot` now `shm_unlink`s `tl_`-prefixed slot paths, and
+  the orphan sweep gained a `ros2_uds_tl_` prefix pass.
+- `DESIGN.md` documents the doorbell wakeup, the graph-event wiring, GID
+  composition and context identity, and the TL ring.
+
+### Fixed
+
+- **`rmw_wait` timeout contract.** The 200 ms poll bound made every wait return
+  `RMW_RET_TIMEOUT` at 200 ms regardless of the caller's deadline — a 600 ms wait
+  returned at 200 ms, and an infinite wait, which must never time out, returned
+  `TIMEOUT`. Idle processes also woke 5×/s. `RMW_RET_TIMEOUT` now surfaces only
+  at the caller's own deadline.
+- **`rmw_wait` reported spurious timeouts** when a drain legitimately yielded
+  nothing (an `ignore_local_publications` drop, or a shm descriptor whose sender
+  is gone).
+- **A wait set holding only guard conditions got a null context** and skipped
+  the registry check entirely — the shape a publish-only node's executor
+  produces. The wait set now stores its context at `rmw_create_wait_set`.
+- **`rmw_wait` dispatched fds the current call never armed.** The armed-fd cache
+  survived across calls and was insert-only, so a guard condition owned by
+  another wait set could have its eventfd consumed with the trigger recorded
+  nowhere — a permanent lost wakeup that hung `wait_for_service` and
+  `GraphListener`. Failed `epoll_ctl` ADDs now degrade to polling instead of
+  being silently dropped.
+- **Dead graph-guard trigger.** `rmw_wait` fired `ctx->graph_guard_condition`, a
+  context-level field that is declared and never assigned, so the branch was
+  dead code and the object `rcl` waits on was never triggered (#43).
+- **Zero-length datagrams were never dequeued.** `recv_from` peeks to size its
+  buffer; a zero-length datagram made the peek return 0 and the function bailed
+  out. `MSG_PEEK` does not consume, so the socket stayed readable forever,
+  spinning every wait that polled that fd.
+- **Junk datagrams are now consumed atomically.** The zero-length cleanup used a
+  blind 1-byte `recv` after a separate, non-atomic peek; under a
+  `MultiThreadedExecutor` a racing drain could consume the peeked datagram and
+  the 1-byte `recv` would dequeue a real message and silently discard it.
+- **Truncated consumes are detected with `MSG_TRUNC` and dropped.** Pre-existing:
+  the consuming `recv` omitted `MSG_TRUNC`, so a concurrently-dequeued peek
+  followed by a larger datagram was silently truncated to the smaller buffer and
+  delivered as valid.
+- **TL: a writer filling a slot the pull scan skipped** opened a sequence gap
+  with `overlapped` left false, defeating the contiguous-prefix trim.
+- **TL: the replay watermark now stops at an unresolvable record.** `max_seq` was
+  fixed before the enqueue loop, so a record whose descriptor could no longer be
+  resolved was skipped while its sequence stayed under the watermark — the
+  sample was lost, not lapped.
+- `rmw_init`'s stale sweep is now stamped, and the throttle-scope comments were
+  corrected.
+- Docs: `TL_RING_MAX_BYTES` was documented as 1 MiB (it is 2 MiB), and the
+  durable-segment budgeting note understated tmpfs sizing for over-cap latched
+  samples (a retained 5 MiB sample costs 5 MiB, not "an inode and a couple of
+  pages"). Reported by Copilot on #60.
+
+### Performance
+
+- **`rmw_wait` drains only the fds `epoll` reported ready** (#57). It previously
+  made three passes over every entity per call — drain every socket, re-arm every
+  fd, drain every socket again — roughly 2150 syscalls for a 719-entity wait set,
+  nearly all returning `EAGAIN` or `EEXIST`.
+- **The stale-slot sweep is throttled off the graph query path** (#58).
+  `query_all` ran `registry_cleanup_stale` before every graph query across 13
+  call sites, so `rmw_get_node_names`, `rmw_count_publishers`,
+  `rmw_count_subscribers`, `rmw_get_topic_names_and_types` and the rest each
+  walked every live slot, copied 1164 bytes out of each, and `stat`ed
+  `/proc/<pid>`.
+- **Launch arithmetic at N=200 nodes:** doorbell datagrams drop from ~100,300
+  (19,900 of them from doorbell self-registration alone) to roughly the number of
+  graph-event consumers; wake-side registry copies go from
+  O(mutations × processes × slots) to zero for plain pub/sub processes.
+- Latched-replay latency improves from ~20 ms (doorbell wake) to synchronous at
+  subscription creation.
+
+### Upgrade notes (0.5.0)
+
+- **Latched replay across a mixed-build pair is lost.** A 0.5.0 publisher no
+  longer push-replays and a pre-0.5.0 subscriber never pulls, so latched replay
+  between that pair does not work during a rolling upgrade — upgrade together
+  (same precedent as the shm payload flag). Old publisher + new subscriber keeps
+  working: an empty `socket_path` skips the pull and the old push path still
+  delivers.
+- **Registry wakeups across a mixed-build fleet can be missed.** A build that
+  predates the doorbell bumps the generation but never rings.
+- **Containers need `--shm-size` ≥ 1 GiB** to run the full test suite. The 64 MB
+  Docker default cannot hold the ~38 MB registry plus the payload rings.
+
+## [0.4.1] - 2026-07-23
+
+### Reverted
+
+- `fix(rmw_wait): deliver TRANSIENT_LOCAL latched samples to late joiners of
+  idle publishers` (#37). The push-based approach woke the publisher process to
+  resend, and the doorbell broadcast it relied on did not scale — every registry
+  mutation rang every process, and every wake rescanned the registry, which
+  melted 200-node launches. Replaced in 0.5.0 by the pull-based ring (#60).
+
+## [0.4.0] - 2026-07-16
+
+### Added
+
+- **Shared-memory ring transport for large topic payloads**, with CDR serialized
+  directly into the ring record.
+- **Durable shm segments for large TRANSIENT_LOCAL messages**, including the
+  serialized-publish path.
+- **Large service request/response payloads routed through shm.**
+- `fork()`-based cross-process shm integration tests.
+
+### Changed
+
+- The inline-vs-shm send/receive decision unified into two helpers.
+- `DESIGN.md` expanded into a fuller architecture document (#16); doc/comment
+  drift from the merge-readiness audit fixed.
+- Repository prepared for open-source release (#15).
+
+### Fixed
+
+- Contained the inline-path resize; the ring inline fallback is now tested.
+- Honest TRANSIENT_LOCAL publish return value.
+
+### Performance
+
+- Shorter `cache_mutex` hold, smaller ring floor, POD-keyed reader cache.
+
+## [0.3.0] - 2026-06-17
+
+Audit hardening & registry/fan-out performance.
+
+### Added
+
+- TRANSIENT_LOCAL replay to late-joining subscribers (#2).
+- README.
+
+### Fixed
+
+- Contained `fastcdr`/`std` exceptions in `serialize()` so none cross the
+  `extern "C"` boundary (#4).
+- Publish a registry slot's state only after its payload commits under the
+  seqlock (#5).
+- Deep-copy `security_options` in `rmw_init_options_copy` to prevent a
+  double-free (#6).
+- Accumulate the `rmw_wait` timeout in `int64` so `RMW_DURATION_INFINITE` keeps
+  blocking (#8).
+- Write `rmw_take_sequence` output at the taken cursor (#7).
+- Surface `EMSGSIZE` as `RMW_RET_ERROR` on publish (#3).
+- Assorted P2/P3 hardening and identifier checks, plus dead-code removal (#9).
+- Probe `localhost_only` via include dirs rather than linked targets, so Rolling
+  configure stops aborting.
+
+### Performance
+
+- Bound query/cleanup scans with a shared high-water mark (#14).
+- Filter registry slots by type before the per-slot snapshot copy (#11).
+- Copy-on-write subscriber-path cache; prune the stale known-subscriber set on
+  graph change (#12).
+- Cache `rmw_service_server_is_available` on the registry generation (#13).
+
+## [0.2.0] - 2026-05-11
+
+Observability.
+
+### Changed
+
+- Failure paths routed through `rcutils` logging.
+- `ament_target_dependencies` replaced with direct `target_link_libraries`.
+- `ament_lint_auto` dropped from the test suite.
+
+### Fixed
+
+- CI: install `test_msgs` explicitly so Rolling stops silently skipping it; tell
+  `rosdep` to install `test_depend` packages; raise `/dev/shm` in the container
+  to 1 GiB.
+
+## [0.1.0] - 2026-05-11
+
+Initial release: a ROS 2 RMW implementation over `AF_UNIX` datagram sockets with
+a lock-free shared-memory registry.
+
+### Added
+
+- Lock-free registry via per-slot seqlock + atomic state.
+- Cached discovery lookups and scale benchmarks.
+- Build & test workflows for Rolling, Jazzy, and Kilted.
+
+### Fixed
+
+- Guard `rmw_init_options_t::localhost_only` behind a CMake probe.
+
+[0.5.0]: https://github.com/benaliabderrahmane/rmw_unix_socket_cpp/compare/v0.4.1...v0.5.0
+[0.4.1]: https://github.com/benaliabderrahmane/rmw_unix_socket_cpp/compare/v0.4.0...v0.4.1
+[0.4.0]: https://github.com/benaliabderrahmane/rmw_unix_socket_cpp/compare/v0.3.0...v0.4.0
+[0.3.0]: https://github.com/benaliabderrahmane/rmw_unix_socket_cpp/compare/v0.2.0...v0.3.0
+[0.2.0]: https://github.com/benaliabderrahmane/rmw_unix_socket_cpp/compare/v0.1.0...v0.2.0
+[0.1.0]: https://github.com/benaliabderrahmane/rmw_unix_socket_cpp/releases/tag/v0.1.0
@@ -22,9 +22,9 @@ datagram sockets; the wait set is `epoll` + `eventfd`.
 
 ## Status
 
-- ROS 2 **Jazzy**, **Kilted**, and **Rolling** — built and tested in CI.
+- ROS 2 **Jazzy**, **Kilted**, **Rolling**, and **Lyrical** — built and tested in CI.
 - **Linux / x86_64 only** (uses `epoll`, `eventfd`, `/dev/shm`, `AF_UNIX`).
-- Version `0.1.0`, Apache-2.0.
+- Version `0.5.0`, Apache-2.0.
 
 ## Quick start
 
 
@@ -2,7 +2,7 @@
 <?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
 <package format="3">
   <name>rmw_unix_socket_cpp</name>
-  <version>0.1.0</version>
+  <version>0.5.0</version>
   <description>
     Lightweight RMW implementation for ROS 2 using Unix domain sockets.
     Designed for localhost-only communication with minimal resource usage.