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lunarfront-app/planning/03_Domain_Inventory.md
Ryan Moon 5f8726ee4e Add planning documents for Forte music store platform 
17 domain design docs covering architecture, accounts, inventory,
rentals, lessons, repairs, POS, payments, batch repairs, delivery,
billing, accounting, deployment, licensing, installer, and backend
tech architecture. Plus implementation roadmap (doc 18) and
personnel management (doc 19).

Key design decisions documented:
- company/location model (multi-tenant + multi-location)
- member entity (renamed from student to support multiple adults)
- Stripe vs Global Payments billing ownership differences
- User/location/terminal licensing model
- Valkey 8 instead of Redis
2026-03-27 14:51:23 -05:00

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Music Store Management Platform
Domain Design: Inventory
Version 1.2 | Updated: Repair Parts Inventory, Bulk Materials, Suppliers
# 1. Overview
The Inventory domain manages all physical items in the store across three distinct inventories: sale inventory (items sold at POS), rental fleet (instruments held for rental), and repair parts inventory (materials consumed in repairs). Each inventory type has different tracking requirements, pricing models, and accounting treatment.
# 2. Inventory Types
Type
Tracking
Appears at POS
Examples
Sale — serialized
Per unit (serial #)
Yes — retail price
Guitars, trumpets, keyboards
Sale — non-serialized
Quantity on hand
Yes — retail price
Strings, reeds, books, picks
Rental fleet
Per unit (serial #)
No — rental only
Student rental instruments
Repair parts — discrete
Qty on hand (integer)
No — repair use only
Valve guides, springs, pads
Repair parts — bulk
Qty on hand (decimal)
No — repair use only
Bow hair, cork sheet, solder
Dual-use
Qty on hand (integer)
Yes — also used in repairs
Strings used in setups, valve oil
Shop supplies
Qty on hand (decimal)
No — overhead cost only
Cleaning patches, lubricant, sandpaper
# 3. Sale Inventory Schema
## 3.1 product
A product is the catalog definition — what an item is, not a specific physical unit. Applies to sale and rental fleet items.
Column
Type
Notes
id
uuid PK
company_id
uuid FK
Tenant scoping
location_id
uuid FK
Physical location — inventory is tracked per-location
sku
varchar
Store SKU
upc
varchar
Manufacturer barcode
name
varchar
description
text
brand
varchar
model
varchar
category_id
uuid FK
Product category
is_serialized
boolean
True = tracked per unit
is_rental
boolean
True = rental fleet item
is_dual_use_repair
boolean
True = also usable in repairs
cost
numeric(10,2)
Supplier cost
price
numeric(10,2)
Default retail price
min_price
numeric(10,2)
Minimum allowed sell price
rental_rate_monthly
numeric(10,2)
Default monthly rental rate
qty_on_hand
integer
Non-serialized items only
qty_reorder_point
integer
Low stock alert threshold
legacy_id
varchar
AIM inventory ID
created_at
timestamptz
## 3.2 inventory_unit
Individual physical units for serialized items and rental fleet instruments.
id, product_id, company_id, location_id, serial_number,condition (new|excellent|good|fair|poor),status (available|sold|rented|in_repair|retired),purchase_date, purchase_cost, notes,legacy_id, created_at
# 4. Repair Parts Inventory
Repair parts are a completely separate inventory from sale items. They are never sold at POS, never appear in the sales catalog, and are tracked specifically for repair cost accounting. The repair parts inventory is accessible only through the repairs module (MOD-REPAIRS).
## 4.1 Part Types
Part Type
Description
Invoice Treatment
billable
Parts charged to customer. Tracked at cost and bill rate.
Appears as line item on invoice at bill_rate
shop_supply
Consumed in repairs but not billed individually. Overhead cost.
Does not appear on invoice
dual_use
Also exists in sale inventory. Repair use decrements sale stock.
Billed at repair rate or retail
flat_rate_material
Material bundled into a flat-rate service charge. E.g. bow hair in a rehair service.
Included in flat rate line item — not itemized
## 4.2 Discrete vs Bulk Parts
Material Type
Tracked As
Examples
Discrete
Integer quantity — whole units only
Valve guides, pad sets, bridge blanks, spring sets
Bulk
Decimal quantity — fractional units allowed
Bow hair (hank), cork sheet, solder (spool), varnish (ml)
Bulk consumable
Decimal — consumed by drops/grams/ml
Lubricant, pad cement, shellac, jewelers rouge
## 4.3 repair_part
Column
Type
Notes
id
uuid PK
company_id
uuid FK
Tenant scoping
location_id
uuid FK
Physical location — repair parts stock is per-location
name
varchar
e.g. 'Bow Hair — Natural White (Standard)'
description
text
part_number
varchar
Manufacturer or supplier part number
part_type
enum
billable | shop_supply | dual_use | flat_rate_material
is_bulk
boolean
True = fractional qty tracking
unit_of_measure
varchar
each | hank | sheet | roll | spool | ml | gram | drop
qty_on_hand
numeric(10,3)
Decimal supports fractional bulk quantities
qty_reorder_point
numeric(10,3)
Low stock alert threshold
cost_per_unit
numeric(10,4)
What store pays per unit — 4 decimal places for small fractions
bill_rate_per_unit
numeric(10,2)
Nullable — what customer is charged per unit if billed per unit
billing_type
enum
per_unit | flat_rate | shop_supply
product_id
uuid FK
Nullable — links to sale inventory for dual_use parts
supplier_id
uuid FK
Primary supplier for reorders
instrument_categories
text[]
Which instrument types use this part
notes
text
is_active
boolean
created_at
timestamptz
## 4.4 repair_part_usage_template
Predefined templates define how much of a bulk material a specific job consumes. Technicians select a template rather than entering quantities manually. Particularly important for bow hair where qty varies by instrument size.
Column
Type
Notes
id
uuid PK
company_id
uuid FK
Tenant scoping
repair_part_id
uuid FK
Which part this template applies to
template_name
varchar
e.g. 'Full size violin bow rehair'
instrument_type
varchar
violin | viola | cello | bass | fractional | other
instrument_size
varchar
4/4 | 3/4 | 1/2 | 1/4 | 1/8 | full
qty_used
numeric(10,3)
Amount consumed e.g. 1.0 hank, 0.67 hank
billing_type
enum
per_unit | flat_rate | shop_supply
flat_rate_desc
varchar
Customer-facing description if flat rate
flat_rate_amount
numeric(10,2)
Nullable — flat rate bill amount
sort_order
integer
Display order in picker UI
created_at
timestamptz
### Default Bow Hair Templates (System Seeded)
Template Name
Instrument
Qty Used
Typical Flat Rate
Full size violin/viola rehair
violin/viola
1.0 hank
$45-55 (store sets)
Cello bow rehair
cello
0.67 hank
$65-80
Bass bow rehair
bass
0.75 hank
$85-100
3/4 violin rehair
violin
0.75 hank
$35-45
1/2 violin rehair
violin
0.60 hank
$30-40
1/4 violin rehair
violin
0.50 hank
$25-35
1/8 and smaller
violin
0.40 hank
$20-30
## 4.5 repair_part_usage
Records each part consumed in a repair ticket. One record per part type per ticket. Referenced by repair_ticket for invoice generation and cost accounting.
Column
Type
Notes
id
uuid PK
repair_ticket_id
uuid FK
repair_part_id
uuid FK
Nullable for custom flat-rate entries
template_id
uuid FK
Nullable — set if selected from template
qty_used
numeric(10,3)
Actual quantity consumed
unit_of_measure
varchar
Recorded at time of use
unit_cost
numeric(10,4)
Cost at time of use — historical accuracy
total_cost
numeric(10,2)
qty_used * unit_cost
billing_type
enum
per_unit | flat_rate | shop_supply
billed_amount
numeric(10,2)
Amount on invoice — 0 for shop_supply
invoice_description
varchar
Customer-facing line item description
created_at
timestamptz
## 4.6 Bulk Material Examples
Material
Unit
Type
Notes
Bow hair — natural white standard
hank
flat_rate_material
Used via templates by bow size
Bow hair — natural white premium
hank
flat_rate_material
Higher grade — higher flat rate
Bow hair — black
hank
flat_rate_material
Bass/cello preference
Cork sheet — 1mm
sheet
billable
Cut to size for neck corks etc
Cork sheet — 2mm
sheet
billable
Thicker applications
Solder — silver bearing
spool
shop_supply
Overhead — not billed
Pad leather — natural
sheet
billable
Cut to size per pad
Shellac flakes
gram
shop_supply
Overhead
Pad cement
ml
shop_supply
Overhead
Valve oil (bulk)
bottle
shop_supply
Overhead — retail valve oil is separate sale item
Cleaning patches
each
shop_supply
Discrete but overhead
Abrasive paper — 220 grit
sheet
shop_supply
Overhead
Resonators — mylar
sheet
billable
Tone holes — billed per replacement
Fingerboard ebony blank
each
billable
Discrete — billed per blank used
Jewelers rouge
gram
shop_supply
Overhead
# 5. Supplier Management
Suppliers are the vendors from whom the store purchases repair parts and sale inventory. Common music repair suppliers include RS Musical, Ferree's Tools, and Allied Supply. Supplier records enable reorder tracking and purchase order generation.
## 5.1 supplier
Column
Type
Notes
id
uuid PK
company_id
uuid FK
Tenant scoping
name
varchar
e.g. 'RS Musical', 'Ferree’s Tools'
contact_name
varchar
Primary contact
email
varchar
phone
varchar
website
varchar
account_number
varchar
Store’s account number with this supplier
payment_terms
varchar
e.g. Net 30, COD, prepaid
notes
text
is_active
boolean
created_at
timestamptz
# 6. Repair Parts Reporting
- Parts on hand — current stock levels across all repair parts
- Low stock alerts — parts at or below reorder point
- Parts usage by period — which parts consumed most frequently
- Parts cost per repair ticket — material cost breakdown
- Technician material usage — parts consumed per technician
- Shop supply expense by period — overhead cost tracking
- Gross margin per repair — revenue vs labor cost vs parts cost
- Bow hair usage analysis — hanks used per month, yield per hank by bow type
- Reorder suggestions — parts below reorder point with preferred supplier
# 7. Business Rules
- Repair parts never appear in sale inventory search or POS catalog
- Dual-use parts decrement sale inventory qty_on_hand when used in repair
- Bulk qty_on_hand uses numeric(10,3) — supports fractional units down to 0.001
- cost_per_unit uses numeric(10,4) — supports very small per-unit costs for bulk materials
- Usage templates are store-configurable — seeded defaults provided, store can modify
- Shop supply parts reduce qty_on_hand but generate no invoice line item
- Flat-rate billing combines material + labor into one customer-facing line item
- Parts cost always recorded at time of use — price changes do not affect historical records
- Negative qty_on_hand not permitted — system warns technician when stock is insufficient
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