occ-conflict-proof-hook

name	occ-conflict-proof-hook
description	Prove optimistic concurrency races in Rust MCP handlers with a deterministic pre-write seam
domain	testing, rust, mcp
confidence	high
source	earned from conversation-memory-foundations memory_close_action closure

Context

When an MCP handler reads a page, mutates content, and writes back with expected_version, race tests become flaky if they depend on thread timing alone.

Pattern

1. Keep the public handler thin and delegate to an internal implementation helper.
2. Let the helper accept a test-only before_write callback that runs after the read/mutation step but before the OCC write.
3. In the conflict test, use that callback to land a competing write first.
4. Assert the handler returns ConflictError and the stored page matches the competing winner, not the stale caller.

Anti-patterns

• Sleep-based race tests
• Adding public debug parameters just to force OCC conflicts
• Asserting source-text ordering instead of observable winner state