docs: document initial_custom_fields on create tracking request

[dodeja]

Rebase of #299 onto current main. The original PR was conflicting (mostly generated Postman churn) while DEV-10929 is already deployed.

What this documents

POST /v2/tracking_requests accepts initial_custom_fields so callers can stage shipment- and container-scoped custom field values before those records exist.

• shipment[] applies to the created shipment (Shipment definitions)
• containers[] applies to matching containers (Container definitions)
• Omit number (or pass "") to broadcast a container value to every container on the shipment

Changes

• OpenAPI request schema + MSC BL example
• Create-tracking-request reference page with a request example
• Regenerated Postman collection from OpenAPI

One small accuracy fix vs #299: the MDX example SCAC is MSCU (not MEDU).

Verification

• git diff --check
• docs/openapi.json parses
• Postman regenerated with openapi2postmanv2

#299 can be closed in favor of this PR.

Test plan

• Confirm the live create-tracking-request contract matches this schema (number vs Linear's original container_number; Container vs Cargo entity type)
• Preview the create-tracking-request page in Mintlify
• After merge, regenerate the TypeScript SDK so createTrackingRequest includes the new field

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Greptile Summary

This PR documents the deployed initial_custom_fields input for creating tracking requests.

• Adds shipment-scoped and per-container custom-field schemas and examples to the OpenAPI source of truth.
• Adds explanatory guidance and a complete request example to the tracking-request reference page.
• Regenerates the Postman collection from the updated OpenAPI specification.

Confidence Score: 5/5

The documentation change appears safe to merge, with no actionable defect established in the changed contract or generated artifacts.

The OpenAPI and MDX representations agree on the new request shape and semantics, while the stale SDK and live-contract verification are explicitly acknowledged follow-up work rather than hidden regressions.

Important Files Changed

Filename	Overview
docs/openapi.json	Adds a consistent initial_custom_fields request schema and example for shipment and container custom-field values.
docs/api-docs/api-reference/tracking-requests/create-a-tracking-request.mdx	Documents definition scoping, targeted container values, and omission or empty-string broadcast semantics.
Terminal49-API.postman_collection.json	Regenerates the collection from OpenAPI; most unrelated changes are nondeterministic IDs and example values rather than new contract changes.

_{Reviews (1): Last reviewed commit: "chore: regenerate Postman collection fro..." | Re-trigger Greptile}

Context used:

• Knowledge Base — Docs Site Structure and OpenAPI Pipeline
• Knowledge Base — TypeScript SDK Client (@terminal49/sdk)

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