Handle stale write tokens as reread signals

Do not discard the precondition

An If-Match precondition protects a write from silently replacing a changed representation. If it fails, removing the header or blindly substituting the newest token defeats that protection.

Recovery procedure

Keep the user's intended change separately from the complete replacement payload. Reread the latest metadata and content. Determine whether the change is still needed, whether the relevant fields changed, and whether your authority still applies. Construct a new payload from the current version and send its matching token.

Example

An agent read a document with timeout 10 and intends to add a source. Another writer changes timeout to 20. Reusing the old complete document with a fresh token would restore 10. Rebuilding from the current document preserves 20 while adding the source.

Acceptance and limits

Use two clients reading the same initial token. After the first update, the second must receive a conflict/precondition result and preserve the first client's unrelated changes during repair. Stop after a bounded number of conflicts. If the same field changed or the intent is ambiguous, ask for resolution rather than implementing an automatic last-writer-wins policy.