fix(acp): bound observer retention by bytes (#7987) - #9436

Co-authored-by: mboston.Engineer <932d3b6ebea6cc83e091551ae46d1c7e7f8f7d0fa8e9cef5e6facc8544af413b@buzz.block.builderlab.xyz>

* origin/main:
  fix(mobile): require Builderlab consent for existing identities (#8823)
  feat(mobile): use HTTP/2 on iOS through app-wide URLSessions (#8897)
  fix(relay): publish a git push only when refs changed; check the protocol by refinement (#9425)
  fix(mobile): show shared chats under Solo (#9348)
  chore(release): release Buzz Desktop version 0.5.29 (#9456)
  feat(mobile): render messages with gpt_markdown 1.3.4 plusparse (#8945)
  fix(acp): bound observer retention by bytes (#7987) (#9436)
  Tune release codegen for faster/smaller binaries (#9434)
  feat(desktop): add dismissible banner pointing to the new buzz app (#9379)
  fix(mobile): keep publishing presence while the app is open (#9441)
  feat(mobile): share into Buzz from the iOS share sheet (#9433)
  fix(mobile): qualify every namesake mention and keep authored mention casing (#9325)
  fix(mobile): match browser GIF timing in the iOS reaction sheet (#9437)
  fix(mobile): play short-delay animation frames at browser speed (#9432)
  buzz-search: read profile names without the profile_name_fields function (#9397)
  buzz-db: build the community deletion lock key in Rust (#9396)
  fix(cli): pair for the active community, skip stopped desktops, accept a bare relay host (#9417)
  test(mobile): run push tests without a gateway dart-define (#9423)
  fix(mobile): never pop Home when archiving from channel settings (#9387)
  perf(acp): reduce observer CPU and lock overhead (#9381)

Signed-off-by: Matthew Boston <[email protected]>

…count-backfill

Co-authored-by: mboston.Engineer <932d3b6ebea6cc83e091551ae46d1c7e7f8f7d0fa8e9cef5e6facc8544af413b@buzz.block.builderlab.xyz>

* bostonaholic--agent-reply-count:
  fix(mobile): require Builderlab consent for existing identities (#8823)
  feat(mobile): use HTTP/2 on iOS through app-wide URLSessions (#8897)
  fix(relay): publish a git push only when refs changed; check the protocol by refinement (#9425)
  fix(mobile): show shared chats under Solo (#9348)
  chore(release): release Buzz Desktop version 0.5.29 (#9456)
  feat(mobile): render messages with gpt_markdown 1.3.4 plusparse (#8945)
  fix(acp): bound observer retention by bytes (#7987) (#9436)
  Tune release codegen for faster/smaller binaries (#9434)
  feat(desktop): add dismissible banner pointing to the new buzz app (#9379)
  fix(mobile): keep publishing presence while the app is open (#9441)
  feat(mobile): share into Buzz from the iOS share sheet (#9433)
  fix(mobile): qualify every namesake mention and keep authored mention casing (#9325)
  fix(mobile): match browser GIF timing in the iOS reaction sheet (#9437)
  fix(mobile): play short-delay animation frames at browser speed (#9432)
  buzz-search: read profile names without the profile_name_fields function (#9397)
  buzz-db: build the community deletion lock key in Rust (#9396)
  fix(cli): pair for the active community, skip stopped desktops, accept a bare relay host (#9417)
  test(mobile): run push tests without a gateway dart-define (#9423)
  fix(mobile): never pop Home when archiving from channel settings (#9387)
  perf(acp): reduce observer CPU and lock overhead (#9381)

Signed-off-by: Matthew Boston <[email protected]>

Replaces #9413 with the packing optimization refreshed against main on a
branch in this repository.

## Summary

Busy agent activity streams repeatedly build and serialize a growing
JSON batch just to check whether the next event fits. Reuse cached event
sizes, measure the newest outer envelope, and build the batch payload
once per completed frame.

Preserve the wire format, greedy packing, per-channel order, channel
barriers, byte budget, and one-frame-per-second relay cadence.
Exact-limit coverage checks escaping, UTF-8, optional metadata, and
array separators. Move the queue tests into a separate module to satisfy
the file-size rule; their test names stay unchanged.

### Related issue

Related to #7987. This builds on the merged fitting/locking work in
#9381 and retention limits in #9436. Closest earlier batching work:
#4917. No duplicate packing fix found among open PRs.

### Testing

The ignored probe fills the production queue before timing, drains every
event, and checks complete FIFO delivery, frame byte limits, and empty
byte accounting.

```sh
CARGO_INCREMENTAL=0 CARGO_PROFILE_RELEASE_LTO=thin CARGO_PROFILE_RELEASE_CODEGEN_UNITS=4 \
  cargo test --release -p buzz-acp --lib observer::packing_tests::publish_queue_drain_probe -- \
  --exact --ignored --nocapture

BUZZ_OBSERVER_PROBE_EVENTS=100 cargo test --release -p buzz-acp --lib \
  observer::packing_tests::publish_queue_drain_probe -- --exact --ignored --nocapture
```

Five alternating fresh release processes per arm and workload compared
baseline `59ae028a3` with candidate `237b928b9` on macOS arm64, Rust
1.98.1. Both arms used `opt-level=3`, thin LTO and four codegen units,
with incremental compilation and compiler-cache wrappers off. Each
executable was rebuilt separately and its probe identity verified.
Medians:

| Events | Before | After | Frames in both arms |
| --- | ---: | ---: | ---: |
| 100 | 6.760 ms | 0.108 ms | 1 |
| 10,000 | 1,597.509 ms | 7.844 ms | 30 |

The one-event control measured 2.04 → 2.21 microseconds. The timed
region covers packing only; ingestion, validation, encryption, publish
pacing, relay delivery, and rendering are excluded. These local results
do not establish an overall app latency improvement. No timing threshold
was added to CI.

Native and deployed-relay latency, independent review, and human
verification remain pending. Keep this PR in draft.

Generated with AI assistance

Signed-off-by: Sanket Kanjalkar <[email protected]>
Co-authored-by: Codex <[email protected]>