Freight Settlement and Electronic Proof of Delivery Webhook Spec

Role: Staff Integration Architect specializing in intermodal supply chain settlement systems.

Context

• Milestone Trigger Events: {{settlement_trigger_events}}
• Signature Verification Standard: {{crypto_signature_algorithm}}
• Financial Ledger Store: {{audit_ledger_backend}}
• Ingestion Retry & Backoff Strategy: {{retry_backoff_policy}}
• Carrier Dispute Grace Period: {{dispute_grace_period}}

Task

Produce an integration and API specification for a resilient freight settlement webhook ingestion engine that validates cryptographic Electronic Proof of Delivery (ePOD) payloads, triggers financial reconciliation, and maintains an immutable audit trail.

Method

1. Define canonical webhook event schemas for each trigger defined in {{settlement_trigger_events}} (e.g., gate-in, geofence departure, digital signature capture, image OCR verification).
2. Specify the payload signing, header standard, and key rotation protocol using {{crypto_signature_algorithm}} to prevent man-in-the-middle tampering.
3. Design a distributed deduplication and idempotency mechanism using deterministic transaction keys.
4. Create the state machine governing the transition from shipment arrival to automated invoice generation and ledger commit inside {{audit_ledger_backend}}.
5. Document the retry orchestration engine including exponential backoff parameters, jitter, and dead-lettering defined by {{retry_backoff_policy}}.
6. Detail the dispute workflow, escrow locking mechanism, and evidence submission APIs active during the {{dispute_grace_period}}.

Constraints

• MUST specify deterministic idempotency keys derived from shipment ID, milestone code, and payload hash.
• MUST NOT process automated settlement credits without validating signature integrity against {{crypto_signature_algorithm}}.
• Database write operations to {{audit_ledger_backend}} MUST be modeled as append-only with double-entry accounting integrity.
• Webhook delivery acknowledgement MUST return HTTP 202 within 300ms, delegating heavy validation to async workers.

Output format

Structure the technical specification into 4 structured components:

1. Webhook Payload Specifications (Complete JSON Schema for all {{settlement_trigger_events}})
2. Cryptographic Security & Header Contract (Signing algorithms, timestamp tolerance, and key rotation)
3. Settlement Lifecycle & State Engine (State transition table and ledger posting rules)
4. Retry, Failure Handling & Dispute Protocols (Algorithmic pseudocode for retries and dispute resolution) Total output must remain under 1,750 words.

Self-review

• Ensure replay attack defenses (e.g., UNIX timestamp drift checks) are explicitly mandated in the verification step.
• Validate that all trigger events in {{settlement_trigger_events}} have dedicated schema representations.
• Confirm the ledger reconciliation model strictly prevents double-crediting across network retries.