ENGINEERING NOTE · SHARED STATE

When two teammates save at the same time.

A shared operations screen creates a risk that a single-user form never has: one valid save can quietly erase another. Kingdom846 refuses the stale write and gives the user a deliberate recovery choice.

System: React → Express → SQLite
Risk: Silent last-write-wins
Response: HTTP 409 Conflict

01 · THE RISK

Valid users can still overwrite valid work.

The War Room is shared by teammates who may open the same roster at the same time. If both clients read version 12, then one user saves version 13 while the other is still editing version 12.

A simple update statement would accept both requests. The later request would look successful even though it was based on stale data, and the first user’s changes would disappear without warning.

EDITOR ALoaded version 12Edits while another user saves

SERVERCurrent version is 13Reject stale save with 409

The server compares versions before it changes the shared record.

02 · THE DECISION

Make the expected version part of every write.

Each read returns the current version. The client sends that version back with its update, and the server compares it with the stored value inside the write path.

If the values match, the update succeeds and the version advances. If they do not match, the server returns a conflict without changing the record. This is optimistic concurrency: editing stays fast, but a stale client cannot silently win.

client version == stored version
    → save changes and increment version

client version != stored version
    → return 409; do not write

03 · THE RECOVERY

A conflict should explain what the user can do next.

Returning 409 protects the data, but it is not enough by itself. The interface shows that a newer version exists and identifies the latest save so the stale editor can understand what happened.

Load the current server version and continue from the teammate’s changes.
Review the difference before trying the edit again.
Replace the current version only through an explicit user choice.
Never present a refused write as a successful save.

04 · THE BOUNDARY

Concurrency control complements authorization.

A version check answers whether the edit is current; it does not answer whether the user is allowed to make it. Kingdom846 also enforces roles on the server so a client cannot grant itself broader access through a modified request.

The result is a clearer boundary: identity and role decide who may write, while the version decides whether that write is safe to apply.