Get listing

Retrieve one active listing owned by the authenticated seller.

Use this endpoint for listing detail pages and edit forms.

Lookup rules:

• Requires listing id path parameter.
• Returns only seller-owned listings with quantity > 0.
• Returns 404 if the listing does not exist or does not belong to the caller.

Response enrichment:

• Joins item metadata from the catalog index.
• Includes seller summary and attachment URLs.
• Computes hold-aware availability:
  • available = quantity - heldQuantity.
  • locked = true when one or more units are currently held.

Failure behavior:

• Returns 400 if the listing exists but its associated item can no longer be resolved.