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The session lease was a compare-and-swap whose fence had leaked into five statements across two crates plus an activation callback that carried the fence into the Cursor journal. This keeps the guarantee and collapses the surface: - `SessionOwnership::claim/release` becomes `SessionLocks::try_lock/unlock`. `try_lock` returns `Option<SessionLock>`; the lock carries the session and an opaque token. Re-locking a session we already hold no longer bumps the token, so the reserve-before-claim ordering hazard is gone. - `create_fenced` / `create_fenced_with_boundary` fold into one `create_locked(log, &lock, boundary)`. The Postgres adapter checks the token once per transaction with `hold_lock` (FOR UPDATE on the session row); the boundary, Cursor checkpoint, and status statements lose their per-statement fence conditions. The unlocked `create` shares `append_log`. - The Cursor journal binds a `SessionLock` instead of (replica, fence), and its row check is the same single statement. `JournalStorage` and `CursorContainerManager::new` drop the replica parameter. - `FencedOut` is now `LockLost`. The lock stays in Postgres on purpose: the check and the write must be one transaction, which a Redis lock cannot give. No schema change; the `manager_fence` column is the token.
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📝 SummarySummary by CodeRabbit
WalkthroughThe PR replaces session claims, ownership outcomes, and manager fences with Priority: ➖ Normal Merge Risk: 🟠 High · up to Concurrent attachments can create duplicate live actors and release a lock while one remains active, risking conflicting session processing. This should be fixed before merge. 🚥 Pre-merge checks | ✅ 3 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (3 passed)
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In `@crates/agent_session/src/domain/ports.rs`:
- Around line 417-419: Share the active reservation registry across
AgentSessionServiceImpl instances that use the same ReplicaId, or validate
ownership of an existing actor before permitting another session start. Preserve
idempotent same-replica re-locking and token behavior in SessionLock and
try_lock, while ensuring concurrent instances cannot obtain the same lock or
allow one actor’s unlock to clear another’s reservation. Add a regression test
covering concurrent locking through two service instances.
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review. Visit https://docs.coderabbit.ai/cli?utm_source=ghpr.
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⛔ Files ignored due to path filters (15)
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📒 Files selected for processing (17)
crates/agent_harness/src/domain/service/test.rscrates/agent_harness/src/outbound/cursor/manager.rscrates/agent_session/src/domain/connection.rscrates/agent_session/src/domain/connection/test.rscrates/agent_session/src/domain/error.rscrates/agent_session/src/domain/model.rscrates/agent_session/src/domain/ports.rscrates/agent_session/src/domain/service.rscrates/agent_session/src/domain/service/test.rscrates/agent_session/src/domain/service/test/owner_binding.rscrates/agent_session/src/outbound/postgres.rscrates/agent_session/src/outbound/postgres/test.rscrates/agent_session/src/testing.rscrates/cursor_cloud_agents/src/outbound/postgres_journal.rscrates/cursor_cloud_agents/src/outbound/postgres_journal/test.rsdocs/CURSOR_AGENT_TRANSPORT.mdservices/agent_harness_service/src/main.rs
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| /// has gone stale. A takeover bumps the session's token; re-locking a session | ||
| /// we already hold does not, so a live actor of ours is never invalidated by | ||
| /// its own replica. See [`SessionLock`](super::model::SessionLock) for why |
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🗄️ Data Integrity & Integration | 🟠 Major | 🏗️ Heavy lift
Share attach exclusion across service instances with the same ReplicaId.
Production creates sessions and inmem_sessions with the same replica, but each AgentSessionServiceImpl::new call creates a separate active registry. Both instances can reserve the same session.
try_lock intentionally preserves the token for same-replica re-locks. Overlapping calls can therefore return the same SessionLock to both actors. Each actor later calls unlock, which matches only the session and token. Either actor can clear the lock while the other actor still runs.
Share the reservation registry across instances, or prove ownership of the existing actor before starting another one. Keep idempotent same-replica re-locking because the established lock contract requires it. Add a concurrent two-instance regression test.
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In `@crates/agent_session/src/domain/ports.rs` around lines 417 - 419, Share the
active reservation registry across AgentSessionServiceImpl instances that use
the same ReplicaId, or validate ownership of an existing actor before permitting
another session start. Preserve idempotent same-replica re-locking and token
behavior in SessionLock and try_lock, while ensuring concurrent instances cannot
obtain the same lock or allow one actor’s unlock to clear another’s reservation.
Add a regression test covering concurrent locking through two service instances.
After applying the fix, consider running `coderabbit review --agent` for local
review. Visit https://docs.coderabbit.ai/cli?utm_source=ghpr.
Keep SessionLocks from this branch and SessionToolCatalog from main in agent_session service imports after both landed on the same lines. Co-authored-by: Wolf Mermelstein <wolf@404wolf.com>
Main added an agent-span tracing test that still called claim_for_test, which this branch renamed to lock_for_test. Co-authored-by: Wolf Mermelstein <wolf@404wolf.com>
2 participants
Why
The agent-session lease was a compare-and-swap whose fence had spread into five SQL statements across two crates, plus an activation callback whose only job was to smuggle the fence into the Cursor journal. Two independent writers (the ACP log writer and the Cursor journal) each did their own
FOR UPDATEcheck on the same row, which is what made #6327 possible.This PR keeps the guarantee and collapses the surface to: you need the session's lock to touch the session, and each write transaction checks the lock once.
The lock stays in Postgres deliberately. The check and the write have to be one transaction, so a stalled replica's late appends are rejected rather than interleaved. A Redis lock cannot give that, and a Redis failover would release every session lock at once. See the doc update in
docs/CURSOR_AGENT_TRANSPORT.md.What changed
SessionOwnership::claim→ClaimOutcome::{Claimed, ManagedElsewhere}SessionLocks::try_lock→Option<SessionLock>SessionClaim { session, replica, fence: ManagerFence }(all public)SessionLock { session, token }(opaque, accessors only)releaseunlockcreate_fenced+create_fenced_with_boundarycreate_locked(log, &lock, boundary)hold_lock(FOR UPDATE) per transaction; the other statements are plainactivate(session, replica, fence)+lock_owneractivate(lock)+ the same singlehold_lockstatementJournalStorage::Postgres { pool, replica },CursorContainerManager::new(.., replica, ..)AgentSessionError::FencedOutLockLostNo schema change.
manager_fenceis the token; renaming the column would churn the sqlx cache for no behavioral gain.Not done here, noted for later: the
AttachmentActivationhook still exists because attachments are built beforeattach_sessiontakes the lock. Removing it meansattach_sessiontaking a builder closure, which touches five call sites inagent_harness.Testing
Against a scratch DB migrated from this branch (
macrodb_wolf1on the wolf9 stack's Postgres):cargo test -p agent_session178 passed. New/adjusted:locking_is_reentrant_and_only_a_takeover_bumps_the_tokenasserts a re-lock returns the same lock and the first lock still writes;history_boundary_rejects_foreign_rows_and_stale_locks_atomicallynow produces the stale lock via a stale heartbeat + successor instead of a self re-claim.cargo test -p cursor_cloud_agents --all-features123 passed.cargo test -p agent_harness191 passed.cargo test -p agent_harness_service30 passed (Redis at the wolf9 stack).cargo sqlx prepare --workspaceregenerated the cache; only the 9 agent-session queries changed (unrelated test-only cache files that the prepare would have dropped were restored).just check,cargo fmt --all -- --check,cargo x deps --check,cargo x kafka-topics --checkclean. Clippy on all targets: one pre-existingunnecessary_sort_byin an untouched test.Hexagonal boundary checked: domain ports carry no sqlx types (
SessionLockis a plain token). Each Postgres adapter that writes session-scoped rows runs the token check inside its own transaction. No authorization or business policy moved. The pre-existingagent_harness/outbound→cursor_cloud_agents::outboundimport is unchanged.Note
Medium Risk
Changes distributed session ownership and all fenced/locked log and Cursor journal writes; behavior is heavily tested but mistakes could allow interleaved writes or break multi-replica attach.
Overview
Refactors agent-session lease/claim/fence semantics into a single per-session lock model while keeping the same safety guarantee: only the holder can write, and stale replicas lose on the next append.
API:
SessionOwnership::claim/SessionClaim/ClaimOutcomebecomeSessionLocks::try_lock/ opaqueSessionLock/Option.release→unlock;create_fenced+create_fenced_with_boundary→create_locked(log, lock, boundary);FencedOut→LockLost. Re-locking a session already held by the same replica no longer bumpsmanager_fence(only a takeover does), so live actors are not invalidated by their own replica.Postgres: Each locked write runs one shared
hold_lock(FOR UPDATE+manager_fencetoken check) per transaction; boundary updates, Cursor checkpoint updates, and journal I/O no longer repeat replica/fence predicates in separate statements.unlockkeys off token only.Cursor:
PgCursorJournalactivates withSessionLockinstead of(replica, fence);CursorContainerManagerdrops the harnessReplicaIdparameter.Tests and docs updated; sqlx query cache regenerated. No schema migration (
manager_fenceremains the token column).Reviewed by Cursor Bugbot for commit e5e7cce. Bugbot is set up for automated code reviews on this repo. Configure here.