One Lane, One Writer
Give each writable resource one writer or a working concurrency control.
The paved path identifies shared resources. Assign write ownership before execution produces the candidate output checked in Factor VII.
The rule
Give each writable resource one writer at a time.
Files, documents, database records and external accounts can all become shared state. A claim in a chat is not a lock, and a second agent does not create a safe second writer.
Use the source system's isolation, locking or guarded update mechanism where concurrent work is authorized. Separate drafts and disjoint scopes help; shared final outputs still need serialized integration.
The evidencesupported
Studies and one engineering report show what goes wrong when agents share a workspace. A single writer is the standard fix from concurrent systems, and no controlled study isolates it.
- CooperBench, 2026: two agents building separate features in one codebase had a 30% lower success rate together than performing both tasks individually. They sent vague and badly timed messages, deviated from their own commitments and held wrong expectations about each other's plans.
- Cursor, 2026 had agents coordinate through a shared file with locks. Agents held locks too long, forgot to release them or wrote without taking one, and twenty agents slowed to the throughput of two or three. Writes that failed when the state had changed proved simpler and more robust.
- Kim et al., 2025 measured error amplification of 17.2 for independent agents against 4.4 for centralized coordination.
- Cognition, 2025 gives the mechanism: each action carries an implicit decision, and conflicting decisions produce bad results.
A 2026 survey, Code as Agent Harness, lists consistent shared state across multiple agents among the field's open problems.
Put it to work
- Identify the resources a job can change before it starts.
- Keep one writer unless the caller authorizes concurrent lanes.
- Give concurrent workers disjoint scopes and suitable isolation.
- Recheck current content before integrating or applying a guarded update.
Example · the monthly operations report
One agent owns the report draft. An authorized helper may investigate a separate source and return cited findings without editing that draft. The draft owner integrates those findings and checks the assembled output.
Failure signal
- Two workers overwrite the same report or record.
- A stale draft silently replaces a newer edit.
- Separate outputs are accepted without checking their integration.
Done looks like
Each changed resource has one writer or a working concurrency control. The integrated output is identifiable and ready for checks.