SPECIMEN 02 / body-blind

The identity mix-up

Same key. Different request.

A changed request body is mistaken for a replay and receives the old receipt.

PUT THE TWO POLICIES SIDE BY SIDE

Same requests. Different memory.

LOCAL MODEL REPLAY

Walk through 4 authored operations. The first visible difference appears at operation 3. Playback illustrates fixed evidence; it does not run an agent or contact a service.

The complete evidence

Always available below, with or without playback.

The identity mix-up: fixed reference and faulty observations. Write counts are cumulative; a dash means no receipt reached the caller.
Operation	Request	Delivery	Correct reference	Faulty policy
01	Tick 0key B · value B	Received	201receipt #1 · writes 1	201receipt #1 · writes 1
02	Tick 1key A · value A	Received	201receipt #2 · writes 2	201receipt #2 · writes 2
03	Tick 2key A · value B	Received	409receipt — · writes 2	200DIFFERSreceipt #2 · writes 2
04	Tick 3key A · value A	Received	200receipt #2 · writes 2	200receipt #2 · writes 2

WHAT MAKES THIS ONE TICK

A small failure, unpacked.

Operation 3 keeps key A but changes its value from A to B. The reference refuses that conflict with 409. The body-blind model returns the old receipt, hiding the fact that this different request was not carried out.

Stripe documents comparing parameters when an idempotency key is reused, and AWS discusses reuse of a request identifier with different intent. Those are background examples of explicit API contracts; this exhibit does not reproduce either service.

TAKEAWAYAn idempotency key identifies an intent. Reusing it with different content needs an explicit policy.

Read the foundations

These sources explain the underlying retry and idempotency concepts. This exhibit is an authored model example, not a claim that a source or vendor contains this fault.

SPECIMEN LABEL / 02

Take it apart.
Take it home.

Evidence: Bundled model comparison
Operations: 4 finite synthetic steps
Fault: body-blind
Boundaries: Keys A/B · values A/B · 6-tick expiry
Provenance: Authored learning fixture

Standalone Node test ↓Candidate JSON ↓Markdown explanation ↓

node --test body-blind.test.mjs

Runs the bundled models locally by default, with no account or network request. To check your implementation, use BUG_ZOO_ADAPTER and the local adapter instructions. Your selected adapter runs with your permissions. The seven-case test kit covers more of the contract. Download asset license: MIT.

THE NEXT MOVE IS YOURS

Can you make it smaller?

This fixture includes removable work. Load it in the contribution workbench, select an operation to remove, and check whether the failure survives. Checking is free of publication; a public contribution requires your deliberate consent.

Remix this specimen ↗Build on an accepted result ↗

An exhibit has no parent receipt. Start from an open handoff to extend an accepted artifact with its exact attribution.

A different failure or interpretation?Bring your own synthetic case ↗Discuss the policy ↗Continue saved work ↗

MEET THE NEXT SPECIMENThe moving deadline