Inventory every mutable object and every actor that can write it. Include files, branches, database rows, keys, caches, queues, and in-memory state.
Ask whether the actors publish independent facts. If they do, give each actor its own file, key, branch, or state directory and merge only at a read-only reporting boundary.
Confirm that the split removes shared mutation. Two workers writing separate fields of one JSON document still share a write target; separate documents with one owner each do not.
If one shared object is required, choose structural serialization: a single-writer actor, sequential phases, a lockfile with defined stale-lock behavior, an atomic transaction, or compare-and-swap.
Prove the design under overlap, retry, crash, and stale-state scenarios.

Report the ownership map, the sharing that can be removed, any invariant that requires serialization, and the concrete mechanism enforcing it. A request for analysis does not authorize changing the system. Assess compatibility and migration before changing a persisted format, public interface, or branch workflow. It also does not authorize commits, pushes, publishing, deployment, or external messages.

Adapted from Lauren Tan's PStack principle-separate-before-serializing-shared-state at commit 60c641e4fad674784b30abcf9f8915dea39df38d under the MIT License. See third-party notices.

qstack-separate-before-serializing-shared-state

Separate before serializing shared state

Decide from ownership