feat(buzz-acp): turn WIP checkpoints + four-way empty outcomes (WO #691)

[Theremoteaidoc]

Summary

Tracks seascope WO: https://github.com/Theremoteaidoc/remote-aid-medical/issues/691
(Buzz issues disabled — closing keyword cannot auto-close the WO; Orchestrator closes block#691 on merge.)

Closes block#691 (seascope WO; hand-close on merge)

SPEC-08 turn checkpointing (crates/buzz-acp):

• wip_checkpoint.rs: OUTBOX/wip/<ts>.bundle drops every 5 min + on termination; latest_wip_bundle picks newest by mtime; split_empty_outcome classifies empty turns.
• HeartbeatState replaces collapsed ReturnedEmpty with KilledTurnCap / KilledIdle / Crashed / Empty.
• pool.rs: sidecar WIP ticker during run_prompt_task; force-drop on cancel/timeout/exit; resume path prepends resume_wip_hint when a WIP bundle exists.
• Negative tripwire: test_wip_outbox_path_outside_branch_watcher_glob — wip/ path cannot match branch-watcher glob (OUTBOX/branch/request.go only).
• Clippy 1.95 -D warnings cleared in touched buzz-acp files (dead_code allow on test-only extend_in_flight_deadline, is_multiple_of, ?, Error::other).

Branch-watcher unchanged (already persona-scoped to OUTBOX/branch/).

files-touched:

• crates/buzz-acp/src/wip_checkpoint.rs
• crates/buzz-acp/src/pool.rs
• crates/buzz-acp/src/lib.rs
• crates/buzz-acp/src/agent_heartbeat.rs
• crates/buzz-acp/src/acp.rs (rustfmt)
• crates/buzz-acp/src/liveness_watcher.rs (rustfmt + clippy)
• crates/buzz-acp/src/queue.rs (rustfmt + clippy allow)
• crates/buzz-acp/tests/initial_heartbeat.rs
• crates/buzz-acp/tests/liveness_watcher.rs

Evidence

=== cargo test -p buzz-acp --lib wip_checkpoint ===
    Finished `test` profile [unoptimized + debuginfo] target(s) in 0.32s
     Running unittests src/lib.rs (target/debug/deps/buzz_acp-cffac62f1d39cfb8)

running 12 tests
test wip_checkpoint::tests::test_latest_wip_bundle_none_when_directory_empty ... ok
test wip_checkpoint::tests::test_maybe_drop_wip_does_not_fire_before_five_minutes ... ok
test wip_checkpoint::tests::test_maybe_drop_wip_fires_at_five_minutes ... ok
test wip_checkpoint::tests::test_split_empty_outcome_agent_exited_is_crashed ... ok
test wip_checkpoint::tests::test_maybe_drop_wip_fires_on_termination_signal_regardless_of_elapsed ... ok
test wip_checkpoint::tests::test_split_empty_outcome_hard_timeout_is_killed_turn_cap ... ok
test wip_checkpoint::tests::test_split_empty_outcome_idle_timeout_is_killed_idle ... ok
test wip_checkpoint::tests::test_split_empty_outcome_ok_no_output_is_empty ... ok
test wip_checkpoint::tests::test_split_empty_outcome_ok_with_message_is_none ... ok
test wip_checkpoint::tests::test_wip_outbox_path_outside_branch_watcher_glob ... ok
test wip_checkpoint::tests::test_latest_wip_bundle_picks_newest_not_alphabetical_first ... ok
test wip_checkpoint::tests::test_kill_at_25_minutes_resumes_from_bundle_within_5_minutes ... ok

test result: ok. 12 passed; 0 failed; 0 ignored; 0 measured; 714 filtered out; finished in 0.02s


=== cargo test -p buzz-acp --lib empty_outcome_timeout_labels ===
    Finished `test` profile [unoptimized + debuginfo] target(s) in 0.32s
     Running unittests src/lib.rs (target/debug/deps/buzz_acp-cffac62f1d39cfb8)

running 1 test
test error_outcome_emission_tests::empty_outcome_timeout_labels_are_killed_not_returned_empty ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 725 filtered out; finished in 0.00s


=== cargo test -p buzz-acp --lib timeout_outcome_labels_differ ===
    Finished `test` profile [unoptimized + debuginfo] target(s) in 0.30s
     Running unittests src/lib.rs (target/debug/deps/buzz_acp-cffac62f1d39cfb8)

running 1 test
test error_outcome_emission_tests::timeout_outcome_labels_differ ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 725 filtered out; finished in 0.01s


=== cargo test -p buzz-acp --lib test_heartbeat_state_as_str ===
    Finished `test` profile [unoptimized + debuginfo] target(s) in 0.31s
     Running unittests src/lib.rs (target/debug/deps/buzz_acp-cffac62f1d39cfb8)

running 1 test
test agent_heartbeat::tests::test_heartbeat_state_as_str_covers_all_four_empty_kinds ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 725 filtered out; finished in 0.00s


=== git diff --stat origin/main...HEAD ===
 crates/buzz-acp/src/acp.rs                 |  30 +--
 crates/buzz-acp/src/agent_heartbeat.rs     | 152 ++++++-----
 crates/buzz-acp/src/lib.rs                 | 253 ++++++++++++-----
 crates/buzz-acp/src/liveness_watcher.rs    |  45 ++--
 crates/buzz-acp/src/pool.rs                |  68 ++++-
 crates/buzz-acp/src/queue.rs               |   7 +-
 crates/buzz-acp/src/wip_checkpoint.rs      | 417 +++++++++++++++++++++++++++++
 crates/buzz-acp/tests/initial_heartbeat.rs |   9 +-
 crates/buzz-acp/tests/liveness_watcher.rs  |  26 +-
 9 files changed, 809 insertions(+), 198 deletions(-)