[teamleaderleo]

Fixes #21000

ACPMUX silently drops outbound messages when a slow client fills its bounded output queue.

The bounded outbound queue now reserves capacity for an RPC response and a recovery marker. When notification delivery is rejected by queue pressure, ACPMUX emits _acpmux/lagged with reason: output_queue_full and a cumulative dropped count so clients can replay from their cursor. Inventory-watch notifications follow the same reserve policy.

Changelog

• ACPMUX reports outbound queue gaps and preserves response/control capacity for reconnect recovery.

Verification

• python3 scripts/cmux-next/prepush-gate.py — passed on 4849c970882c9dd7b2cefc4b9e359152e7541a95.
• cargo fmt --manifest-path cmux-tui/Cargo.toml --all -- --check — passed.
• Hosted focused verification run 40068104184 is bound to the exact head; Linux test is still running. Other jobs have independent runner/base failures (MSRV, macOS setup, cross-build, clippy/panic ratchet) and are recorded as base/infrastructure findings.

Agent session: huge-blue

---

^{Need help on this PR? Tag @codesmith-bot with what you need.}

---

Summary by cubic

Fixes outbound queue backpressure in ACPMUX so slow clients get a replay signal instead of silently dropped notifications, while always reserving capacity for RPC responses.

• Reserves queue slots for responses and the _acpmux/lagged recovery marker so notifications can't crowd out replies.
• Queues _acpmux/lagged with reason: output_queue_full and a cumulative dropped count when notifications are dropped; oversized notifications report reason: message_too_large.
• Serializes capacity checks and enqueues across request, inventory-watch, and inventory-disable paths so gap delivery and the disable reply stay ordered; when the queue is full, the marker waits for the next free slot so even a quiet reader eventually receives it.
• Closes pending gap waiters when the connection tears down, so no task leaks after disconnect.

^{Written for commit 3c72e64. Summary will update on new commits.}

[github-actions]

cmux status _{(one comment, edited in place; each line is updated by the job that owns it)}

Review 3c72e64: HQ feed card · gallery before/after runs · checks

App of this head (app.zip, kept 1 day)

gh workflow run reload-build.yml -R manaflow-ai/cmux --ref feat-cmux-next -f tag=pr24811 -f ref=nx-21000 -f platform=macos -f backend_mode=local

red: cmux-next checks (god files, concurrency, crash safety, l10n); no finished base run on eac20cf to compare; do not merge until green; see lane-rules

[blacksmith-sh]

Found 12 test failures on Blacksmith runners:

Failures

Test	View Logs
/tmp/tmphxdelwmr/summary-missing.json (live):/summary-missing.json (live):	View Logs
/tmp/tmpnytm78rc/summary-fail.json (live):/summary-fail.json (live):	View Logs
[new_workspaces] debug.new_workspace timed 0 of 50 new workspace rows/ [new_workspaces] debug.new_workspace timed 0 of 50 new workspace rows	View Logs
[new_workspaces] the window draws no frames/[new_workspaces] the window draws no frames	View Logs
[tabs] debug.tab_switch timed 0 of 40 switches/ [tabs] debug.tab_switch timed 0 of 40 switches	View Logs
[tabs] the window draws no frames/[tabs] the window draws no frames	View Logs
convention violations found (ERROR lines above)./ convention violations found (ERROR lines above).	View Logs
test_base_passes (main.NoticesPairTests.test_base_passes)/ test_base_passes (main.NoticesPairTests.test_base_passes)	View Logs
test_bot_attempt_three_drops_stale_owned_pool_placement (main.PathRoutingStructure. test_bot_attempt_three_drops_stale_owned_pool_placement)/ test_bot_attempt_three_drops_stale_owned_pool_placement (main.PathRoutingStructure. test_bot_attempt_three_drops_stale_owned_pool_placement)	View Logs
test_notices_for_another_ghostty_next_commit_fail (main.NoticesPairTests.test_notic es_for_another_ghostty_next_commit_fail)/ test_notices_for_another_ghostty_next_commit_fail (main.NoticesPairTests.test_notic es_for_another_ghostty_next_commit_fail)	View Logs

...and 2 more test failures. View all on Blacksmith: run 40085833211, run 40085833162

^{Need help on this PR? Tag @codesmith-bot with what you need.}

[teamleaderleo]

Bead cx-g1dnw created for this PR by the cmux coordinator.

[teamleaderleo]

Review note: Conn::send uses a bounded Sender::capacity() check before try_send; concurrent fan-out/request producers can race at the reserve boundary. The focused regression exercises the slow-reader path with one producer. I am preserving this exact head while the ACPMUX review broker is unavailable; no speculative redesign is included.

[cursor]

Bugbot needs on-demand usage enabled

Bugbot uses usage-based billing for this team and requires on-demand usage to be enabled.

A team admin can enable on-demand usage in the Cursor dashboard.

[github-actions]

Shipped in:

• cmux NEXT nightly 1.0.0-nightly.4009633177301 (812000d772)
• cmux NEXT nightly 1.0.0-nightly.4009794369001 (9287623e69)