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train_bge_v5.py

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+# /// script
+# requires-python = ">=3.10"
+# dependencies = [
+#     "sentence-transformers>=3.0.0",
+#     "torch",
+#     "transformers>=4.40.0",
+#     "numpy",
+#     "datasets",
+#     "accelerate>=1.1.0",
+# ]
+#
+# [tool.uv.sources]
+# torch = [
+#     { index = "pytorch-cu124", marker = "sys_platform == 'linux'" },
+# ]
+#
+# [[tool.uv.index]]
+# name = "pytorch-cu124"
+# url = "https://download.pytorch.org/whl/cu124"
+# explicit = true
+# ///
+"""
+BGE-large comparison: automotive embedding fine-tuning + evaluation.
+
+Fine-tunes BAAI/bge-large-en-v1.5 (335M params) to compare against
+nomic-embed-text-v1.5 (137M) on the same PCAdb subcategory retrieval task.
+
+Run on HF: hf jobs uv run --flavor a100-large --timeout 30m --namespace <ns> train_bge.py
+"""
+
+import json
+import os
+import random
+import sys
+import tempfile
+from pathlib import Path
+
+import numpy as np
+from sentence_transformers import InputExample, SentenceTransformer, losses
+from torch.utils.data import DataLoader
+
+random.seed(42)
+np.random.seed(42)
+
+# ============================================================================
+# BENCHMARK — DO NOT MODIFY
+# 55 concerns (49 real + 1 garbage). This is the fixed evaluation set.
+# ============================================================================
+
+BENCHMARK = [
+    {"concern": "Replace front brake pads and rotors", "expected_subcategories": ["Brake > Disc Pads and Brake Shoes", "Brake > Drums and Rotors"]},
+    {"concern": "Brake pads worn to backing", "expected_subcategories": ["Brake > Disc Pads and Brake Shoes"]},
+    {"concern": "Replace front shocks and struts", "expected_subcategories": ["Suspension > Shocks and Struts"]},
+    {"concern": "Control arm bushing worn", "expected_subcategories": ["Suspension > Suspension, Springs and Related Components"]},
+    {"concern": "Timing chain replacement needed", "expected_subcategories": ["Engine > Valve Train Components"]},
+    {"concern": "Serpentine belt cracking", "expected_subcategories": ["Belts and Cooling > Accessory Drive Belt System Components"]},
+    {"concern": "Battery dead needs replacement", "expected_subcategories": ["Electrical, Charging and Starting > Battery and Related Components"]},
+    {"concern": "Alternator failing low voltage", "expected_subcategories": ["Electrical, Charging and Starting > Alternator / Generator and Related Components"]},
+    {"concern": "Fuel pump making noise", "expected_subcategories": ["Air and Fuel Delivery > Fuel Pumps and Related Components"]},
+    {"concern": "A/C compressor not engaging", "expected_subcategories": ["HVAC > A/C Clutch and Compressor"]},
+    {"concern": "Power steering pump leak", "expected_subcategories": ["Steering > Power Steering Hoses, Pumps, and Related Components"]},
+    {"concern": "Spark plugs replacement due", "expected_subcategories": ["Ignition > Secondary Ignition"]},
+    {"concern": "Wiper blades streaking", "expected_subcategories": ["Wiper and Washer > Wiper Arm, Blade, and Related Components"]},
+    {"concern": "Wheel bearing noise from front", "expected_subcategories": ["Driveline and Axles > Wheel Bearings, Seals, and Related Components"]},
+    {"concern": "Synthetic Oil Service due", "expected_subcategories": ["Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)"]},
+    {"concern": "Power steering flush needed", "expected_subcategories": ["Steering > Power Steering Hoses, Pumps, and Related Components", "Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)"]},
+    {"concern": "Differential service recommended", "expected_subcategories": ["Driveline and Axles > Differential", "Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)"]},
+    {"concern": "Transfer case fluid change", "expected_subcategories": ["Transfer Case > Transfer Case Components", "Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)"]},
+    {"concern": "BRAKE PAD WORN", "expected_subcategories": ["Brake > Disc Pads and Brake Shoes"]},
+    {"concern": "AC recharge needed blowing warm", "expected_subcategories": ["HVAC > A/C Clutch and Compressor"]},
+    {"concern": "r&r radiator", "expected_subcategories": ["Belts and Cooling > Radiators, Coolers and Related Components"]},
+    {"concern": "Vehicle pulls right", "expected_subcategories": ["Suspension > Alignment"]},
+    {"concern": "CEL on rough running", "expected_subcategories": ["Ignition > Secondary Ignition"]},
+    {"concern": "Mailer oil change", "expected_subcategories": ["Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)"]},
+    {"concern": "ATF flush", "expected_subcategories": ["Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)"]},
+    {"concern": "Brak pads worn", "expected_subcategories": ["Brake > Disc Pads and Brake Shoes"]},
+    {"concern": "upper mount plate", "expected_subcategories": ["Suspension > Shocks and Struts"]},
+    {"concern": "mirror assembly", "expected_subcategories": ["Body > Mirrors"]},
+    {"concern": "grinding noise when braking", "expected_subcategories": ["Brake > Disc Pads and Brake Shoes"]},
+    {"concern": "car won't start clicking", "expected_subcategories": ["Electrical, Charging and Starting > Starter and Related Components"]},
+    {"concern": "clunking over bumps", "expected_subcategories": ["Suspension > Shocks and Struts"]},
+    {"concern": "overheating", "expected_subcategories": ["Belts and Cooling > Radiators, Coolers and Related Components"]},
+    {"concern": "a/c blowing warm", "expected_subcategories": ["HVAC > A/C Clutch and Compressor"]},
+    {"concern": "rotten egg smell", "expected_subcategories": ["Exhaust > Catalytic Converter"]},
+    {"concern": "clicking when turning", "expected_subcategories": ["Driveline and Axles > CV Components"]},
+    {"concern": "whining when turning", "expected_subcategories": ["Steering > Power Steering Hoses, Pumps, and Related Components"]},
+    {"concern": "humming from wheel area", "expected_subcategories": ["Driveline and Axles > Wheel Bearings, Seals, and Related Components"]},
+    {"concern": "squealing belt noise", "expected_subcategories": ["Belts and Cooling > Accessory Drive Belt System Components"]},
+    {"concern": "oil leak from top of engine", "expected_subcategories": ["Engine > Gaskets and Sealing Systems"]},
+    {"concern": "loud exhaust", "expected_subcategories": ["Exhaust > Mufflers"]},
+    {"concern": "Replace catalytic converter", "expected_subcategories": ["Exhaust > Catalytic Converter"]},
+    {"concern": "CV axle boot torn", "expected_subcategories": ["Driveline and Axles > CV Components", "Driveline and Axles > CV Boots and Related Components"]},
+    {"concern": "Cabin air filter replacement", "expected_subcategories": ["HVAC > Filters"]},
+    {"concern": "Blower motor not working", "expected_subcategories": ["HVAC > Motors, Core, Case and Related Components"]},
+    {"concern": "EGR valve stuck", "expected_subcategories": ["Emission Control > EGR and Related Components"]},
+    {"concern": "TPMS light on", "expected_subcategories": ["Tire and Wheel > Sensors"]},
+    {"concern": "New tires needed", "expected_subcategories": ["Tire and Wheel > Tire"]},
+    {"concern": "Turbo boost leak", "expected_subcategories": ["Air and Fuel Delivery > Turbocharger, Supercharger and Ram Air"]},
+    {"concern": "customer wants alignment check", "expected_subcategories": ["Suspension > Alignment"]},
+    {"concern": "Complete garbage text 12345 xyz", "expected_subcategories": []},
+]
+
+# ============================================================================
+# === EXPERIMENT ZONE === (modify freely below this line)
+# ============================================================================
+
+# -- Hyperparameters --
+BASE_MODEL = "BAAI/bge-large-en-v1.5"
+EPOCHS = 10
+BATCH_SIZE = 64
+LEARNING_RATE = 3e-5
+WARMUP_RATIO = 0.1
+MATRYOSHKA_DIMS = []  # Disabled — dilutes gradient across dims
+GARBAGE_THRESHOLD = 0.3
+
+# -- Training Data --
+
+KEYWORD_TO_SUBCATEGORIES = [
+    # Suspension
+    {"keywords": ["shock", "strut", "loaded strut", "quick strut"], "subcategories": ["Suspension > Shocks and Struts"]},
+    {"keywords": ["control arm", "ball joint", "sway bar", "stabilizer bar", "stabilizer link", "tie rod", "track bar"], "subcategories": ["Suspension > Suspension, Springs and Related Components"]},
+    {"keywords": ["coil spring", "leaf spring", "spring assembly"], "subcategories": ["Suspension > Suspension, Springs and Related Components"]},
+    {"keywords": ["alignment", "camber", "caster", "toe"], "subcategories": ["Suspension > Alignment"]},
+    # Brake
+    {"keywords": ["brake pad", "brake shoe"], "subcategories": ["Brake > Disc Pads and Brake Shoes"]},
+    {"keywords": ["brake rotor", "brake drum", "rotor"], "subcategories": ["Brake > Drums and Rotors"]},
+    {"keywords": ["brake caliper", "caliper bracket", "brake hose"], "subcategories": ["Brake > Brake Hydraulics"]},
+    {"keywords": ["brake fluid", "brake bleed", "brake flush"], "subcategories": ["Brake > Brake System Service", "Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)"]},
+    {"keywords": ["abs system", "abs sensor", "abs module", "abs pump", "abs light", "anti-lock"], "subcategories": ["Brake > ABS Components"]},
+    # Engine
+    {"keywords": ["valve cover", "head gasket", "intake manifold gasket", "exhaust manifold gasket", "oil pan gasket"], "subcategories": ["Engine > Gaskets and Sealing Systems"]},
+    {"keywords": ["timing chain", "timing belt", "camshaft", "crankshaft", "rocker arm", "lifter", "engine valve", "intake valve", "exhaust valve"], "subcategories": ["Engine > Valve Train Components"]},
+    {"keywords": ["piston", "engine block", "connecting rod", "main bearing", "cylinder sleeve", "cylinder liner"], "subcategories": ["Engine > Cylinder Block Components"]},
+    # Belts and Cooling
+    {"keywords": ["serpentine", "drive belt", "belt tensioner", "idler pulley"], "subcategories": ["Belts and Cooling > Accessory Drive Belt System Components"]},
+    {"keywords": ["radiator", "radiator hose"], "subcategories": ["Belts and Cooling > Radiators, Coolers and Related Components"]},
+    {"keywords": ["coolant", "antifreeze"], "subcategories": ["Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)"]},
+    {"keywords": ["water pump"], "subcategories": ["Belts and Cooling > Water Pump and Related Components"]},
+    {"keywords": ["thermostat"], "subcategories": ["Belts and Cooling > Thermostat and Housing"]},
+    {"keywords": ["cooling fan", "fan clutch", "fan motor", "radiator fan"], "subcategories": ["Belts and Cooling > Cooling Fan, Clutch and Motor"]},
+    {"keywords": ["coolant hose", "heater hose"], "subcategories": ["Belts and Cooling > Hoses and Pipes"]},
+    # Air and Fuel Delivery
+    {"keywords": ["fuel pump", "fuel pump assembly", "fuel sender"], "subcategories": ["Air and Fuel Delivery > Fuel Pumps and Related Components"]},
+    {"keywords": ["fuel injector", "fuel rail", "throttle body", "throttle"], "subcategories": ["Air and Fuel Delivery > Fuel Injection System and Related Components"]},
+    {"keywords": ["air filter", "intake filter"], "subcategories": ["Air and Fuel Delivery > Filters"]},
+    {"keywords": ["fuel tank", "fuel filler"], "subcategories": ["Air and Fuel Delivery > Fuel Storage"]},
+    {"keywords": ["turbo", "turbocharger", "supercharger", "intercooler", "wastegate", "boost"], "subcategories": ["Air and Fuel Delivery > Turbocharger, Supercharger and Ram Air"]},
+    # Electrical
+    {"keywords": ["battery", "battery cable", "battery terminal"], "subcategories": ["Electrical, Charging and Starting > Battery and Related Components"]},
+    {"keywords": ["alternator", "generator"], "subcategories": ["Electrical, Charging and Starting > Alternator / Generator and Related Components"]},
+    {"keywords": ["starter", "starter motor"], "subcategories": ["Electrical, Charging and Starting > Starter and Related Components"]},
+    # Emission Control
+    {"keywords": ["catalytic converter", "cat converter"], "subcategories": ["Exhaust > Catalytic Converter"]},
+    {"keywords": ["oxygen sensor", "o2 sensor"], "subcategories": ["Emission Control > Sensors"]},
+    {"keywords": ["egr", "egr valve"], "subcategories": ["Emission Control > EGR and Related Components"]},
+    {"keywords": ["evap", "purge valve", "charcoal canister", "vapor canister"], "subcategories": ["Emission Control > Evaporative System"]},
+    {"keywords": ["pcv", "pcv valve"], "subcategories": ["Emission Control > Crankcase Ventilation System"]},
+    # Exhaust
+    {"keywords": ["muffler"], "subcategories": ["Exhaust > Mufflers"]},
+    {"keywords": ["exhaust pipe", "exhaust manifold", "flex pipe", "resonator"], "subcategories": ["Exhaust > Exhaust and Tail Pipes", "Exhaust > Exhaust Manifolds"]},
+    # Ignition
+    {"keywords": ["spark plug"], "subcategories": ["Ignition > Secondary Ignition"]},
+    {"keywords": ["ignition coil", "coil pack", "coil on plug"], "subcategories": ["Ignition > Ignition Coil"]},
+    {"keywords": ["plug wire", "ignition wire"], "subcategories": ["Ignition > Ignition Wire and Related Components"]},
+    {"keywords": ["distributor"], "subcategories": ["Ignition > Distributor and Magneto"]},
+    # Steering
+    {"keywords": ["power steering pump", "power steering hose", "power steering fluid", "power steering flush", "power steering"], "subcategories": ["Steering > Power Steering Hoses, Pumps, and Related Components", "Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)"]},
+    {"keywords": ["rack and pinion", "steering gear", "steering rack", "inner tie rod", "outer tie rod"], "subcategories": ["Steering > Steering, Gear and Related Components"]},
+    {"keywords": ["steering column"], "subcategories": ["Steering > Steering Column"]},
+    # Transmission
+    {"keywords": ["transmission fluid", "trans fluid", "atf", "transmission flush"], "subcategories": ["Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)"]},
+    {"keywords": ["clutch", "flywheel", "clutch disc", "pressure plate", "throwout bearing"], "subcategories": ["Transmission > Clutch Plates", "Transmission > Flywheel"]},
+    {"keywords": ["torque converter"], "subcategories": ["Transmission > Automatic Transmission Components"]},
+    # Driveline
+    {"keywords": ["cv axle", "cv joint", "cv boot"], "subcategories": ["Driveline and Axles > CV Components", "Driveline and Axles > CV Boots and Related Components"]},
+    {"keywords": ["drive shaft", "u-joint", "universal joint"], "subcategories": ["Driveline and Axles > Drive Shaft"]},
+    {"keywords": ["differential", "diff fluid", "diff service"], "subcategories": ["Driveline and Axles > Differential", "Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)"]},
+    {"keywords": ["wheel bearing", "hub bearing", "hub assembly"], "subcategories": ["Driveline and Axles > Wheel Bearings, Seals, and Related Components", "Driveline and Axles > Hubs and Related Components"]},
+    # Transfer Case
+    {"keywords": ["transfer case"], "subcategories": ["Transfer Case > Transfer Case Components", "Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)"]},
+    # HVAC
+    {"keywords": ["a/c compressor", "ac compressor"], "subcategories": ["HVAC > A/C Clutch and Compressor", "Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)"]},
+    {"keywords": ["a/c condenser", "ac condenser", "evaporator"], "subcategories": ["HVAC > A/C Condenser and Evaporator", "Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)"]},
+    {"keywords": ["refrigerant", "freon", "a/c recharge", "ac recharge", "a/c service", "ac service"], "subcategories": ["HVAC > A/C Clutch and Compressor", "Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)"]},
+    {"keywords": ["blower motor", "blower resistor"], "subcategories": ["HVAC > Motors, Core, Case and Related Components"]},
+    {"keywords": ["cabin filter", "cabin air filter"], "subcategories": ["HVAC > Filters"]},
+    {"keywords": ["heater core"], "subcategories": ["HVAC > Air Heater Components"]},
+    # Tire and Wheel
+    {"keywords": ["tire", "tyre"], "subcategories": ["Tire and Wheel > Tire"]},
+    {"keywords": ["wheel", "rim", "lug nut"], "subcategories": ["Tire and Wheel > Wheel"]},
+    {"keywords": ["tpms", "tire pressure sensor"], "subcategories": ["Tire and Wheel > Sensors"]},
+    # Wiper and Washer
+    {"keywords": ["wiper", "wiper blade"], "subcategories": ["Wiper and Washer > Wiper Arm, Blade, and Related Components"]},
+    {"keywords": ["washer fluid", "washer pump", "windshield washer"], "subcategories": ["Wiper and Washer > Windshield Washer and Related Components"]},
+    # Oil and Chemicals
+    {"keywords": ["oil change", "oil service", "motor oil", "engine oil", "synthetic oil", "oil filter"], "subcategories": ["Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)", "Engine > Filters"]},
+    {"keywords": ["brake cleaner", "dielectric grease", "anti-seize", "thread locker", "penetrating oil"], "subcategories": ["Oil, Fluids and Chemicals > Cleaners and Removers", "Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)"]},
+]
+
+VARIANT_TEMPLATES = [
+    "Replace {kw}",
+    "R&R {kw}",
+    "{kw} replacement",
+    "{kw} replacement needed",
+    "Install new {kw}",
+    "{kw} is bad",
+    "{kw} failing",
+    "{kw} worn out",
+    "{kw} leaking",
+    "{kw} noise",
+    "needs {kw}",
+    "new {kw}",
+    "{kw} - replace",
+    "Customer states {kw} issue",
+    "Check and replace {kw}",
+    "Recommend {kw} replacement",
+]
+
+SYMPTOM_VARIANTS = [
+    # Brakes — pads/shoes
+    {"symptoms": [
+        "grinding noise when braking", "squealing when stopping", "brake pedal goes to floor",
+        "pulsating brake pedal", "car pulls when braking", "scraping sound when stopping",
+        "metal on metal when braking", "grinding from front when stopping",
+        "high pitched squeal stopping", "brakes feel spongy",
+    ], "subcategories": ["Brake > Disc Pads and Brake Shoes"]},
+    # Brakes — rotors/drums
+    {"symptoms": [
+        "steering wheel shakes when braking", "vibration when stopping",
+        "pulsation in pedal at highway speed", "shimmy when braking",
+        "warped rotors vibration", "shudder when applying brakes",
+    ], "subcategories": ["Brake > Drums and Rotors"]},
+    {"symptoms": ["abs light on", "anti-lock brake warning", "abs fault code", "traction control light and abs light"], "subcategories": ["Brake > ABS Components"]},
+    # Suspension — shocks/struts (expert-expanded)
+    {"symptoms": [
+        "clunking over bumps", "vehicle bounces excessively", "nose dives when stopping",
+        "rough ride", "bouncy ride", "car keeps bouncing after bumps",
+        "thump over speed bumps", "leaking strut", "front end bottoming out",
+        "rear sags under load", "knocking over potholes", "harsh ride quality",
+        "suspension feels loose", "banging noise hitting bumps",
+        "front end clunk", "noise over railroad tracks",
+        "bang over bumps", "thud from front end", "knock over rough road",
+        "chassis slap over bumps", "double thump speed bumps",
+        "front end bangs dips", "rear clunk over bumps", "trunk area thump bumps",
+        "rattle over small bumps", "suspension noise over potholes",
+        "clunk from front suspension", "rear suspension thump",
+        "noise over expansion joints", "knocks on washboard road",
+        "clunk over driveway apron", "noise from strut area over bumps",
+    ], "subcategories": ["Suspension > Shocks and Struts"]},
+    # Suspension — strut mounts (expert-expanded)
+    {"symptoms": [
+        "upper mount plate", "strut mount noise", "top mount bearing worn",
+        "upper strut mount", "mount plate clunking", "popping when turning steering wheel stationary",
+        "creaking from top of strut tower", "strut plate bearing",
+        "upper strut plate", "mount plate bearing", "strut tower mount",
+        "top mount worn", "upper spring seat", "strut top hat",
+        "mount plate popping", "bearing plate noise turning",
+        "strut mount bearing noisy", "upper mount clunk", "top hat binding",
+        "spring seat cracked", "mount bearing seized",
+        "pop while steering from strut mount", "front mount plate noise",
+        "upper mount separated",
+    ], "subcategories": ["Suspension > Shocks and Struts"]},
+    # Suspension — alignment (expert-expanded)
+    {"symptoms": [
+        "vehicle pulls to one side", "uneven tire wear", "steering wheel off center",
+        "vehicle pulls right", "vehicle pulls left", "car drifts right",
+        "car drifts left", "steering wheel crooked", "feathering on tires",
+        "cupping on tires", "car doesn't track straight", "pulls to the right on highway",
+        "pulls to right", "drifts right on flat road", "steering pulls",
+        "needs alignment pulls", "alignment off pulls right", "tracks right",
+        "wanders on highway", "won't hold straight line",
+        "off center steering wheel", "lane drift", "darting on highway",
+    ], "subcategories": ["Suspension > Alignment"]},
+    # Suspension — control arms/bushings (expert-expanded)
+    {"symptoms": [
+        "clunk when turning", "loose steering feel",
+        "control arm bushing worn", "worn control arm bushings",
+        "sway bar link rattle", "stabilizer bar noise",
+        "ball joint play", "loose front end", "front end clunk turning",
+        "bushing cracked", "bushing deteriorated", "lower control arm play",
+        "LCA bushing torn", "compliance bushing shot",
+        "control arm rear bushing split", "bushing separated",
+        "arm bushing excessive movement", "thrust arm bushing cracked",
+        "front end looseness low speed", "clunk turning and braking",
+        "hydro bushing leaking", "rear compliance bushing torn",
+        "FCA bushing worn", "RCA bushing worn",
+    ], "subcategories": ["Suspension > Suspension, Springs and Related Components"]},
+    # Engine — gaskets
+    {"symptoms": ["oil leak from top of engine", "burning oil smell", "oil seeping from valve cover", "wet around intake"], "subcategories": ["Engine > Gaskets and Sealing Systems"]},
+    # Engine — timing/valve train (expert-expanded)
+    {"symptoms": [
+        "rattling on cold start", "timing noise", "engine ticking",
+        "timing chain replacement needed", "timing chain stretched",
+        "timing chain rattle", "chain slap on startup", "variable valve timing code",
+        "cam phaser noise", "vvt solenoid", "engine timing off",
+        "chain stretched", "timing chain code", "P0016 cam crank correlation",
+        "P0017 cam position", "timing set replacement", "chain guides worn",
+        "cold start chain rattle", "chain noise on startup", "chain slack",
+        "cam crank out of sync", "correlation fault", "chain tensioner weak",
+        "guides broken", "phaser correlation fault",
+        "cam timing over retarded", "cam timing over advanced",
+        "engine rattles first start", "chain kit recommended",
+        "front cover timing repair", "timing chain needed",
+    ], "subcategories": ["Engine > Valve Train Components"]},
+    # Cooling
+    {"symptoms": ["overheating", "temperature gauge high", "coolant on ground", "coolant leak", "steam from hood"], "subcategories": ["Belts and Cooling > Radiators, Coolers and Related Components"]},
+    {"symptoms": [
+        "squealing belt noise", "belt chirping on startup",
+        "serpentine belt cracking", "belt squeal", "chirping from front of engine",
+        "belt slipping when wet", "cracked belt", "belt glazed",
+    ], "subcategories": ["Belts and Cooling > Accessory Drive Belt System Components"]},
+    # Electrical
+    {"symptoms": ["car won't start", "clicking when turning key", "no crank", "slow crank", "starter grinds"], "subcategories": ["Electrical, Charging and Starting > Starter and Related Components"]},
+    {"symptoms": ["battery light on", "dim headlights", "electrical issues", "charging system warning"], "subcategories": ["Electrical, Charging and Starting > Alternator / Generator and Related Components"]},
+    {"symptoms": ["dead battery", "battery keeps dying", "battery won't hold charge", "needs jump every morning"], "subcategories": ["Electrical, Charging and Starting > Battery and Related Components"]},
+    # Ignition — CEL/misfire (expert-expanded)
+    {"symptoms": [
+        "CEL on", "check engine light", "misfire", "rough idle", "rough running",
+        "CEL on rough running", "engine misfiring", "stumbles at idle",
+        "rough running check engine light", "cylinder misfire code",
+        "P0300 random misfire", "P0301 misfire cylinder 1", "hesitation under acceleration",
+        "tune up needed", "tune-up", "engine tune up",
+        "CEL rough running", "CEL with misfire", "check engine rough idle",
+        "MIL on running rough", "SES light rough idle", "CEL P0300",
+        "CEL multiple misfire", "engine light on stumbling",
+        "CEL on with shaking", "service engine soon rough",
+        "misfiring under load", "flashing CEL misfire",
+        "sputtering with check engine light", "shaking at idle CEL",
+        "rough idle with codes", "stumble and check engine light",
+        "P0301", "P0302", "P0303", "P0304",
+        "random misfire", "multiple cylinder misfire",
+        "bucks and jerks with CEL",
+    ], "subcategories": ["Ignition > Secondary Ignition"]},
+    # Ignition — spark plugs maintenance (expert-expanded)
+    {"symptoms": [
+        "spark plugs replacement due", "plugs due for service", "100k spark plug service",
+        "plugs due", "spark plug service", "60k plug change",
+        "100k plug service", "iridium plugs due", "platinum plugs worn",
+        "plug gap too wide", "mileage-based plug replacement", "maintenance plugs",
+        "tune up due", "due for plugs per mileage", "recommend spark plugs",
+        "plugs worn", "electrodes worn", "plugs original",
+        "overdue for spark plugs", "plug service due by maintenance schedule",
+        "replace plugs as maintenance",
+    ], "subcategories": ["Ignition > Secondary Ignition"]},
+    # HVAC — A/C (expert-expanded)
+    {"symptoms": [
+        "a/c blowing warm", "no cold air", "a/c not working",
+        "AC recharge needed blowing warm", "ac not cold enough",
+        "ac recharge needed", "a/c weak", "a/c warm on one side",
+        "refrigerant low", "ac blows hot", "air conditioning not cooling",
+        "AC recharge", "A/C recharge needed", "freon low",
+        "134a recharge", "1234yf recharge", "ac charge and check",
+        "air not blowing cold", "AC performance check",
+        "AC system evacuation and recharge", "AC evac and recharge",
+        "low refrigerant", "static pressure low", "recharge and leak test",
+        "recover evacuate recharge", "recharge with dye",
+        "not cooling at idle", "vent temp high", "AC weak",
+        "warm air from vents",
+    ], "subcategories": ["HVAC > A/C Clutch and Compressor"]},
+    {"symptoms": ["no heat", "heater not working", "heat blows cold", "lukewarm heat", "heater weak"], "subcategories": ["HVAC > Air Heater Components"]},
+    # HVAC — blower motor (expert-expanded)
+    {"symptoms": [
+        "blower motor not working", "no air from vents", "fan not blowing",
+        "blower only works on high", "hvac fan stopped", "no air flow from dash",
+        "blower resistor", "fan speed not changing", "only high speed works on fan",
+        "HVAC fan dead", "cabin fan stopped", "no air movement dash",
+        "blower quit working", "heat fan not blowing", "fan motor seized",
+        "blower motor intermittent", "no fan from vents", "blower inop",
+        "interior fan not working", "no blower on any speed",
+        "blower resistor concern", "fan cuts in and out",
+        "no airflow from vents", "HVAC blower intermittent",
+    ], "subcategories": ["HVAC > Motors, Core, Case and Related Components"]},
+    # Exhaust — muffler
+    {"symptoms": ["loud exhaust", "exhaust leak", "rumbling underneath", "exhaust drone", "holes in muffler"], "subcategories": ["Exhaust > Mufflers"]},
+    # Exhaust — catalytic converter (expert-expanded)
+    {"symptoms": [
+        "rotten egg smell", "catalytic converter code", "sulfur smell from exhaust",
+        "P0420 catalyst efficiency", "P0430 catalyst", "cat efficiency below threshold",
+        "rotten egg odor", "exhaust smells like eggs", "failing catalytic converter",
+        "egg smell from exhaust", "sulfur odor driving", "rotten smell tailpipe",
+        "hydrogen sulfide smell", "cat going bad smell", "stinky exhaust",
+        "exhaust smells terrible", "rotten smell after hard acceleration",
+        "bad catalyst smell", "converter smell", "strong sulfur exhaust odor",
+        "rotten egg smell under load", "sulfur smell after highway drive",
+    ], "subcategories": ["Exhaust > Catalytic Converter"]},
+    # Steering — power steering (expert-expanded)
+    {"symptoms": [
+        "whining when turning", "hard to steer", "power steering whine",
+        "whining noise turning wheel", "groan when turning steering wheel",
+        "steering stiff", "fluid leaking from steering rack",
+        "whine at low speed turns", "moaning sound turning",
+        "power steering fluid low", "ps pump noise",
+        "whine at full lock", "pump noise turning", "moan turning wheel",
+        "steering whine low speed", "PS pump whine", "groan turning at idle",
+        "howling when steering", "fluid cavitation noise turning",
+        "power steering noisy", "steering pump moans",
+        "whine when parking", "groan backing out while turning",
+        "steering noise cold", "aerated PS fluid", "low PS fluid noise",
+    ], "subcategories": ["Steering > Power Steering Hoses, Pumps, and Related Components"]},
+    # Driveline — CV
+    {"symptoms": ["clicking when turning", "cv clicking", "clicking noise in turns", "cv axle popping"], "subcategories": ["Driveline and Axles > CV Components"]},
+    # Driveline — wheel bearings (expert-expanded)
+    {"symptoms": [
+        "humming from wheel area", "wheel noise at speed", "growling noise from front",
+        "humming gets louder with speed", "bearing noise",
+        "roaring sound from wheel", "drone changes with steering input",
+        "wheel hum goes away turning one direction", "rumble from rear axle area",
+        "hub bearing noise", "grinding from front wheel",
+        "hum from front wheel", "droning noise road speed", "wheel rumble highway",
+        "noise changes turning left right", "growl from hub area",
+        "bearing drone 40mph plus", "hum louder faster you go",
+        "helicopter noise road speed", "wheel bearing growl",
+        "drone from left front", "drone from right front",
+        "noise unloads on turns", "hub noise",
+        "rumble from corner of vehicle",
+    ], "subcategories": ["Driveline and Axles > Wheel Bearings, Seals, and Related Components"]},
+    # Body — mirrors
+    {"symptoms": [
+        "mirror assembly", "mirror replacement", "side mirror broken",
+        "mirror glass cracked", "power mirror not working", "mirror folding mechanism",
+        "driver side mirror", "passenger mirror", "rear view mirror fell off",
+        "mirror turn signal", "blind spot mirror",
+    ], "subcategories": ["Body > Mirrors"]},
+    # Tire — TPMS (expert-expanded)
+    {"symptoms": [
+        "TPMS light on", "tire pressure light", "tire pressure warning",
+        "tpms sensor", "tire monitor light", "low tire pressure warning",
+        "tpms fault", "tire pressure monitoring light",
+        "tire light on dash", "TPMS warning", "tire monitor fault",
+        "low tire light stays on after fill", "TPMS sensor battery dead",
+        "tire pressure indicator", "TPMS relearn needed",
+        "tire pressure light flashing", "sensor not detected",
+        "tire pressure monitor inop", "tpms service",
+        "no sensor signal", "relearn tire sensors", "sensor battery low",
+    ], "subcategories": ["Tire and Wheel > Sensors"]},
+    # Fluids — ATF (expert-expanded)
+    {"symptoms": [
+        "ATF flush", "ATF change", "transmission fluid service",
+        "trans fluid flush", "automatic transmission fluid",
+        "transmission fluid dark", "burnt trans fluid",
+        "ATF exchange", "ATF drain and fill", "automatic transmission fluid service",
+        "transmission service ATF", "ATF dark needs flush",
+        "ATF maintenance", "trans fluid exchange",
+        "transmission fluid service due", "CVT fluid service",
+        "DSG service", "pan drop and filter", "trans service by mileage",
+        "burnt ATF", "fluid discolored", "fluid exchange recommended",
+        "service transmission fluid", "trans fluid change",
+    ], "subcategories": ["Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)"]},
+    # Fluids — oil change with marketing prefix
+    {"symptoms": [
+        "Mailer oil change", "oil change special", "coupon oil change",
+        "promo oil change", "mail-in oil change", "oil change deal",
+        "customer came in for oil change", "just here for an oil change",
+        "routine oil change", "express oil change", "quick lube oil change",
+    ], "subcategories": ["Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)"]},
+    # ====================== EXPANDED TRAINING DATA (v3+) ======================
+    # Category 1: Catalytic Converter / Exhaust (expanded)
+    {"symptoms": [
+        "rotten egg smell from exhaust", "smells like sulfur", "eggs smell when I drive it",
+        "bad exhaust smell", "stinks out the tailpipe", "nasty smell coming from exhaust",
+        "exhaust smells rich", "exhaust smells burnt", "fumes smell weird",
+        "sulfer smell", "sulphur smell", "egg smell from car",
+        "cat smell bad", "converter smell", "clogged cat", "plugged cat",
+        "stopped up cat", "bad catalytic converter", "cat code stored",
+        "P0420 in memory", "P0430 stored", "catalyst efficiency code",
+        "bank 1 cat low efficiency", "bank 2 cat low efficiency",
+        "failed emissions for cat", "won't get out of its own way",
+        "no power uphill and smells", "runs hot and smells funny",
+        "glowing cat underneath", "rattle in catalytic converter",
+        "something loose in exhaust", "honeycomb busted in cat",
+        "cat material broke apart", "exhaust restriction", "restricted exhaust",
+        "backpressure high", "muffled exhaust flow", "sounds choked up",
+        "tailpipe barely blowing", "smells like burning chemicals",
+        "fume smell in cabin", "cat is toast", "cat's smoked",
+        "converter stopped up", "catylitic converter bad", "cadillac converter bad",
+        "cad converter issue", "cat con bad", "replace front pipe/cat",
+        "after cat damaged", "downstream cat code", "upstream cat failure",
+        "MIL on for catalyst", "check engine light for cat",
+        "exhaust smells like ass", "smells like something died in exhaust",
+        "smells like cat pee", "smells like ammonia from exhaust",
+        "sounds like marbles in a can",
+    ], "subcategories": ["Exhaust > Catalytic Converter"]},
+    # Category 2: Starter / No-Start (expanded)
+    {"symptoms": [
+        "car won't start, just clicks", "single click no start",
+        "rapid clicking when turning key", "click click click won't start",
+        "no crank no start", "won't crank", "won't turn over",
+        "doesn't even try to start", "dead on the lot", "dead in driveway",
+        "won't fire up", "starter just spins", "starter freewheels",
+        "grinding when starting", "hard start then nothing",
+        "intermittent no start", "starts sometimes",
+        "have to turn key a few times", "push button does nothing",
+        "key on and nothing happens", "dash lights on but no crank",
+        "all lights come on but won't start", "battery seems fine but won't start",
+        "slow crank", "cranks real slow", "lazy starter", "drags when cranking",
+        "long crank then starts", "cranks but won't start",
+        "turns over but won't fire", "starter sticking", "solenoid clicking",
+        "starter relay maybe", "tap starter and it starts",
+        "starts after hitting starter", "hot soak no start",
+        "won't start when hot", "starts cold not hot", "starter heat soak",
+        "dead spot in starter", "starter hangs up", "locked up starter",
+        "starter seized", "starter out", "bad starter motor",
+        "needs starter/sol", "starter engagement noise",
+        "starter stays engaged", "starter keeps spinning after start",
+        "no start concern", "vehicle will not crank",
+        "cust states no start", "c/s heard one click",
+        "c/s intermittent crank/no crank", "c/s engine won't rotate by key",
+        "RO: no crank verified", "RO: starter inop",
+        "RO: starter drawing high amps", "starter bad", "strtr bad",
+        "n/s condition", "nc/ns",
+    ], "subcategories": ["Electrical, Charging and Starting > Starter and Related Components"]},
+    # Category 3: Ignition / Check Engine Light (expanded)
+    {"symptoms": [
+        "check engine light on, running rough", "CEL on", "MIL on",
+        "SES light on", "service engine soon light", "engine light came on",
+        "check eng lite on", "check motor light", "running rough",
+        "rough idle", "idles rough", "shaking at idle", "engine shaking",
+        "car is sputtering", "hesitates on takeoff", "stumble on acceleration",
+        "bucks when accelerating", "jerks under load", "missing", "has a miss",
+        "misfire", "multiple misfire", "cyl 3 misfire",
+        "P0300", "P0301", "P0302", "P0303", "P0304",
+        "coil code", "bad coil maybe", "spark plugs due",
+        "needs tune up", "needs plugs and coils",
+        "cuts out going uphill", "breaks up under load",
+        "feels like it's dropping a cylinder", "sounds like a Subaru now",
+        "flashing check engine light", "CEL blinking", "MIL flashing",
+        "loss of power with engine light", "hard start and rough run",
+        "runs like crap", "runs like dog shit", "engine chugging",
+        "surging at idle", "vibration from engine", "hesitation from stop",
+        "popping through intake", "backfiring", "afterfire out exhaust",
+        "fuel smell and misfire", "wet plug", "fouled plug",
+        "burnt coil boot", "arc mark on coil", "secondary ignition fault",
+        "ignition breakdown", "coil pack bad", "coil rail issue",
+        "bad plug wire", "spark leak", "engine skips", "skip in engine",
+        "rough on cold start", "misfire when wet/raining",
+        "starts and stumbles", "won't rev clean",
+        "poor acceleration, no codes yet", "customer says needs tune-up",
+        "RO: ck eng lt on, misfire felt", "RO: rough run/poor accel",
+        "RO: scanned codes p030x", "c/s vehicle shudders at stops",
+        "c/s engine hiccups", "it only does it when it rains",
+        "sounds like popcorn under the hood",
+    ], "subcategories": ["Ignition > Secondary Ignition"]},
+    # Category 4: Cooling System / Overheating (expanded)
+    {"symptoms": [
+        "car is overheating", "running hot", "temp gauge high",
+        "temperature climbing", "needle almost in the red", "temp pegged hot",
+        "engine got hot", "overheated on freeway", "overheats in traffic",
+        "overheats at idle", "overheats with AC on", "steam from hood",
+        "smoke from hood but not smoke", "coolant leaking", "antifreeze leak",
+        "losing coolant", "have to keep adding coolant", "low coolant light on",
+        "coolant smell", "sweet smell from engine bay", "puking coolant",
+        "blowing coolant out", "spits coolant out reservoir",
+        "overflow bottle boiling", "coolant reservoir empty",
+        "reservoir keeps overflowing", "radiator cracked", "radiator leaking",
+        "hose blew off", "upper hose rock hard", "coolant all over engine bay",
+        "green fluid under car", "orange fluid under car", "pink fluid leaking",
+        "cust states engine hot", "c/s overheating concern", "c/s temp light on",
+        "check gauges message", "hot coolant warning", "engine over temp message",
+        "over temp shut down", "limp mode from overheating",
+        "coolant disappearing no visible leak", "pressure test failed",
+        "cooling system won't hold pressure", "rad cap bad",
+        "bad cap causing boil over", "needs radiator",
+        "air pocket in system", "air locked cooling system",
+        "boiling over", "hot but then goes back down", "temp fluctuates",
+    ], "subcategories": ["Belts and Cooling > Radiators, Coolers and Related Components"]},
+    # Category 4b: Cooling — thermostat specific
+    {"symptoms": [
+        "thermostat stuck", "thermostat not opening",
+        "needs thermostat housing", "temp gauge drops on the freeway",
+    ], "subcategories": ["Belts and Cooling > Thermostat and Housing"]},
+    # Category 4c: Cooling — water pump specific
+    {"symptoms": [
+        "water pump leaking", "water pump making noise",
+    ], "subcategories": ["Belts and Cooling > Water Pump and Related Components"]},
+    # Category 4d: Cooling — fan specific
+    {"symptoms": [
+        "fans not coming on", "cooling fan inop", "fan only works with AC",
+        "fan roaring all the time", "fan runs after I shut car off",
+    ], "subcategories": ["Belts and Cooling > Cooling Fan, Clutch and Motor"]},
+    # Category 4e: Cooling — heater / coolant crossover symptoms
+    {"symptoms": [
+        "heater blows cold then hot", "no heat and overheating",
+        "bubbles in coolant bottle", "gurgling in dash",
+        "gurgling in cooling system", "heater quits when gauge goes high",
+        "heater only gets hot when I'm driving",
+        "smells like syrup in the car",
+    ], "subcategories": ["HVAC > Air Heater Components"]},
+    # Category 5: Strut Mounts / Upper Mounts (expanded)
+    {"symptoms": [
+        "upper mount plate worn", "strut mount bad", "top hat bad",
+        "top mount bad", "upper strut mount loose", "mount plate noisy",
+        "bearing plate bad", "strut bearing noisy",
+        "popping from front end", "front end clunk",
+        "thunk over speed bumps", "knock from left front",
+        "knock from right front", "noise when turning steering wheel",
+        "spring bind when turning", "creaks when turning",
+        "boing noise from front", "rubber twisting noise",
+        "pops backing out of driveway", "clunk when entering driveway",
+        "noise at top of strut", "play in upper mount",
+        "mount separated", "strut tower noise", "bearing seized in mount",
+        "steering notchy at low speed", "spring snaps when steering",
+        "front suspension popping", "suspension clunk over rough roads",
+        "rattle from strut area", "metal on metal from upper mount",
+        "top of strut moving", "mount collapsed", "mount blown out",
+        "mount mushroomed", "worn strut hats", "upper isolator bad",
+        "strut mount bearing plate", "front coilover mount noise",
+        "noise from cowl area over bumps", "sounds like loose shock",
+        "sounds like loose suspension bolt",
+        "customer says something up top is loose",
+        "RO: clunk from upper mounts", "RO: inspect strut mount brg",
+        "RO: top plate play noted", "RO: mount brg binding",
+        "c/s popping LF over bumps", "c/s front end creak when turning",
+        "strt mnt noisy", "upper plate worn", "bearing plate seized",
+        "steering snaps back weird after turn",
+    ], "subcategories": ["Suspension > Shocks and Struts"]},
+    # Category 6: Turbocharger / Boost (new)
+    {"symptoms": [
+        "turbo boost leak", "no boost", "not making boost",
+        "turbo not kicking in", "feels naturally aspirated now",
+        "no power till forever", "turbo lag bad", "laggy as hell",
+        "boost leak noise", "whooshing under acceleration",
+        "air noise when boosting", "hiss under boost", "whistle changed",
+        "turbo whining", "siren noise from turbo", "dentist drill noise",
+        "wastegate rattle", "rattle on decel from turbo",
+        "underboost code", "overboost code", "P0299", "P0234",
+        "boost pressure low", "boost too high", "limp mode turbo",
+        "goes into limp when I get on it", "reduced power with turbo",
+        "charge pipe blew off", "intercooler leak", "split boost hose",
+        "CAC leak", "turbo seals leaking", "smokes after boost",
+        "burning oil from turbo", "oil in intercooler pipes",
+        "shaft play in turbo", "turbo seized", "turbo blown",
+        "turbo toast", "bad turbocharger", "waste gate stuck",
+        "wastegate actuator bad", "boost solenoid bad",
+        "diverter valve issue", "BOV leaking", "surging under boost",
+        "cuts out in boost", "won't build boost past 5 psi",
+        "overboosting and fuel cuts", "flutter noise", "compressor surge",
+        "spools then falls flat", "boost comes and goes",
+        "slow spool", "late spool", "whistle then no power",
+        "check engine light with turbo code", "epc light with no boost",
+        "customer says turbo sounds louder", "customer says turbo quit",
+        "RO: verify underboost", "RO: boost leak suspected",
+        "RO: turbocharger noisy", "RO: wg rattle noted",
+        "turbski bad", "turbski no chooch", "no chooch from turbo",
+        "not spooling", "not spoolin", "boost dump noise", "charge air leak",
+        "whistles when I accelerate",
+    ], "subcategories": ["Air and Fuel Delivery > Turbocharger, Supercharger and Ram Air"]},
+    # Category 7: Wheel Alignment (expanded)
+    {"symptoms": [
+        "customer requests alignment check", "needs alignment",
+        "alignment feels off", "pulls left", "pulls right",
+        "drifts left", "drifts right", "won't track straight",
+        "have to hold steering wheel crooked", "steering wheel off center",
+        "wheel is crooked going straight", "steering not centered",
+        "dog tracking", "crab walking", "wanders on highway",
+        "all over the road", "feels loose on freeway",
+        "uneven tire wear", "inside tire wear", "outside tire wear",
+        "feathered tires", "cupping on tires",
+        "new tires need alignment", "after hitting pothole",
+        "after curb hit", "after accident alignment check",
+        "after suspension work needs alignment",
+        "after tie rod replacement", "after struts needs alignment",
+        "after control arm replacement", "shimmy and pull",
+        "tracks weird", "veers when braking", "pulls on crowned roads",
+        "rear feels like it steers itself",
+        "steering wheel not straight after repair",
+        "toe looks off", "camber off", "caster issue", "alignment out",
+        "front end alignment", "4 wheel alignment", "thrust angle issue",
+        "set the toe", "straighten wheel",
+        "pulling since I bought tires", "eating tires",
+        "chewing up front tires", "wearing out rear tires funny",
+        "customer says it don't drive straight",
+        "RO: ck/aln", "RO: align after front end work",
+        "RO: steer wheel off ctr", "RO: pulls R verify",
+        "RO: abnormal tire wear, chk alignment",
+        "c/s vehicle drifts", "c/s wheel crooked",
+        "needs front end lined up",
+    ], "subcategories": ["Suspension > Alignment"]},
+    # Category 8: Oil Change / Coupon / Mailer (expanded)
+    {"symptoms": [
+        "came in with mailer for oil change", "coupon oil change",
+        "mailer special oil change", "LOF", "lube oil filter",
+        "lube, oil, filter", "oil service", "synthetic service",
+        "full syn oil service", "conventional oil service",
+        "blend oil change", "express oil change", "quick lube service",
+        "basic service special", "maintenance special",
+        "5k service", "5000 mile service", "3k service", "7,500 mile service",
+        "routine maintenance", "due for service", "service due light on",
+        "maintenance light on for oil", "oil life says 15%",
+        "oil life monitor on", "change oil soon message",
+        "change engine oil message", "oil reset needed",
+        "annual oil service", "came in for advertised oil special",
+        "internet coupon for oil change", "mail flyer oil special",
+        "postcard oil change deal", "seasonal service special",
+        "winter service oil change", "first free oil change",
+        "complimentary oil change", "prepaid maintenance oil service",
+        "works package / oil service", "tire rotation and oil change special",
+        "LOF/tire rotate", "oil/filter change", "engine oil and filter",
+        "minor service", "A service", "B service with oil",
+        "factory maintenance due", "scheduled maintenance",
+        "PM service", "preventive maintenance", "pit stop service",
+        "customer says just needs fluids and oil",
+        "cust here for sticker oil change", "the little light says oil",
+        "my oil percentage is low", "needs oil and reset",
+        "came in with $29.95 oil coupon", "came in with ValPak oil coupon",
+        "came in from postcard offer", "RO: customer requests LOF",
+        "RO: perform LOF", "RO: oil svc per coupon",
+        "RO: maint light on / oil change",
+        "RO: customer here for advertised special",
+    ], "subcategories": ["Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)"]},
+    # ====================== BONUS: Symptom → Repair Patterns ======================
+    # Brake — rotors/pulsation
+    {"symptoms": [
+        "car shakes when I brake", "vibration when stopping at highway speed",
+        "steering wheel shakes when braking at 65",
+    ], "subcategories": ["Brake > Drums and Rotors"]},
+    # Brake — hydraulics
+    {"symptoms": [
+        "brake pedal goes to floor", "pedal is hard as a rock",
+        "brake pedal spongy",
+    ], "subcategories": ["Brake > Brake Hydraulics"]},
+    # Brake — stuck caliper
+    {"symptoms": [
+        "smells hot after driving", "smells like brakes after short drive",
+    ], "subcategories": ["Brake > Brake Hydraulics"]},
+    # Battery — parasitic draw
+    {"symptoms": [
+        "battery keeps dying overnight", "radio and dash reboot when I start it",
+    ], "subcategories": ["Electrical, Charging and Starting > Battery and Related Components"]},
+    # Belt — serpentine off
+    {"symptoms": [
+        "all the lights came on and steering got hard",
+        "chirp chirp chirp from engine", "it sounds supercharged now",
+    ], "subcategories": ["Belts and Cooling > Accessory Drive Belt System Components"]},
+    # Engine — valve train / detonation
+    {"symptoms": [
+        "ticking after oil change", "sounds like marbles in a can",
+    ], "subcategories": ["Engine > Valve Train Components"]},
+    # Engine — mounts
+    {"symptoms": [
+        "thumps when I stop", "clunk when shifting into drive",
+        "shudders taking off",
+    ], "subcategories": ["Engine > Engine and Transmission Mounts"]},
+    # Exhaust — leak / flex pipe
+    {"symptoms": [
+        "car sounds louder but only when accelerating",
+        "exhaust leak at flex pipe", "loud exhaust and smell",
+        "needs exhaust manifold/cat",
+    ], "subcategories": ["Exhaust > Exhaust and Tail Pipes"]},
+    # Exhaust — heat shield
+    {"symptoms": [
+        "rattles underneath at idle",
+    ], "subcategories": ["Exhaust > Exhaust and Tail Pipes"]},
+    # Emission Control — EVAP
+    {"symptoms": [
+        "gas smell after I fill up", "takes forever to fill gas tank",
+        "gas pump keeps clicking off",
+    ], "subcategories": ["Emission Control > Evaporative System"]},
+    # Driveline — u-joint / lash
+    {"symptoms": [
+        "thunk when I let off the gas",
+    ], "subcategories": ["Driveline and Axles > Drive Shaft"]},
+    # Tire — slow leak
+    {"symptoms": [
+        "one tire keeps going low", "flaps or slaps at highway speed",
+    ], "subcategories": ["Tire and Wheel > Tire"]},
+    # Tire — balance / vibration
+    {"symptoms": [
+        "steering wheel shakes at 65", "vibration at highway speed",
+        "sounds like an airplane on the highway",
+    ], "subcategories": ["Tire and Wheel > Tire"]},
+    # Suspension — springs / lean
+    {"symptoms": [
+        "car leans on one side", "my truck squats in the back",
+        "rear end wiggles over bumps",
+    ], "subcategories": ["Suspension > Suspension, Springs and Related Components"]},
+    # HVAC — blend door actuator
+    {"symptoms": [
+        "clicking in dash", "no heat on passenger side",
+    ], "subcategories": ["HVAC > Motors, Core, Case and Related Components"]},
+    # HVAC — water on floor
+    {"symptoms": [
+        "water on passenger floor", "smoke from the vents",
+    ], "subcategories": ["HVAC > A/C Condenser and Evaporator"]},
+    # Transfer case
+    {"symptoms": [
+        "4x4 light flashing",
+    ], "subcategories": ["Transfer Case > Transfer Case Components"]},
+    # ABS / traction
+    {"symptoms": [
+        "traction light and ABS light on together",
+    ], "subcategories": ["Brake > ABS Components"]},
+    # Engine — gaskets / oil smell
+    {"symptoms": [
+        "can smell oil but no drips", "white smoke only in the morning",
+    ], "subcategories": ["Engine > Gaskets and Sealing Systems"]},
+    # Air and Fuel — throttle / limp
+    {"symptoms": [
+        "won't go over 20 mph", "gas pedal does nothing sometimes",
+        "engine races at stoplights", "car falls on its face",
+        "black smoke when I punch it",
+    ], "subcategories": ["Air and Fuel Delivery > Fuel Injection System and Related Components"]},
+]
+
+SYMPTOM_TEMPLATES = [
+    "{symptom}",
+    "Customer states {symptom}",
+    "C/S {symptom}",
+    "Complaint: {symptom}",
+    "Concern: {symptom}",
+    "Vehicle has {symptom}",
+    "Car {symptom}",
+    "Inspect for {symptom}",
+    "Diag for {symptom}",
+    "Check {symptom}",
+    # Expert-added: DMS/shop shorthand prefixes
+    "Cust states {symptom}",
+    "States {symptom}",
+    "Complains of {symptom}",
+    "Chk and advise {symptom}",
+    "Check and advise {symptom}",
+    "Inspect and advise {symptom}",
+    "Found {symptom}",
+    "Verified {symptom}",
+    "Confirmed {symptom}",
+    "Recommend {symptom}",
+    "Rec {symptom}",
+    "LF {symptom}",
+    "RF {symptom}",
+    "LR {symptom}",
+    "RR {symptom}",
+    "Front {symptom}",
+    "Rear {symptom}",
+]
+
+COMMON_TYPOS = {
+    "brake": ["brak", "brke", "barke"],
+    "rotor": ["roter", "rotot"],
+    "strut": ["strutt", "strrt"],
+    "alternator": ["alternater", "alterntor"],
+    "thermostat": ["thermistat", "thermstat", "thermastat"],
+    "serpentine": ["serpantine", "serpentene"],
+    "catalytic": ["catalitic", "catylitic", "catalyic"],
+    "differential": ["differntial", "diferential"],
+    "compressor": ["compresser", "compresser"],
+    "radiator": ["raditor", "raidator"],
+    "transmission": ["transmision", "trnasmission"],
+    "steering": ["steerin", "stearing"],
+    "exhaust": ["exaust", "exhuast"],
+    "alignment": ["alignemnt", "aligment"],
+    "battery": ["baterry", "batter"],
+    "coolant": ["coolent", "coollant"],
+    "muffler": ["mufler", "mufflar"],
+}
+
+HARD_NEGATIVES = [
+    # --- Original hard negatives ---
+    {"query": "replace radiator", "positive": "Belts and Cooling > Radiators, Coolers and Related Components", "negative": "Transmission > Radiators, Coolers and Related Components"},
+    {"query": "r&r radiator", "positive": "Belts and Cooling > Radiators, Coolers and Related Components", "negative": "Transmission > Radiators, Coolers and Related Components"},
+    {"query": "radiator leaking", "positive": "Belts and Cooling > Radiators, Coolers and Related Components", "negative": "Transmission > Radiators, Coolers and Related Components"},
+    {"query": "radiator hose replacement", "positive": "Belts and Cooling > Radiators, Coolers and Related Components", "negative": "Transmission > Radiators, Coolers and Related Components"},
+    {"query": "transmission cooler", "positive": "Transmission > Radiators, Coolers and Related Components", "negative": "Belts and Cooling > Radiators, Coolers and Related Components"},
+    {"query": "trans cooler line leaking", "positive": "Transmission > Radiators, Coolers and Related Components", "negative": "Belts and Cooling > Radiators, Coolers and Related Components"},
+    {"query": "timing chain replacement", "positive": "Engine > Valve Train Components", "negative": "Driveline and Axles > Drive Shaft"},
+    {"query": "timing belt worn", "positive": "Engine > Valve Train Components", "negative": "Belts and Cooling > Accessory Drive Belt System Components"},
+    {"query": "spark plug replacement", "positive": "Ignition > Secondary Ignition", "negative": "Ignition > Ignition Coil"},
+    {"query": "new spark plugs", "positive": "Ignition > Secondary Ignition", "negative": "Ignition > Ignition Coil"},
+    {"query": "CEL on rough running", "positive": "Ignition > Secondary Ignition", "negative": "Electrical, Charging and Starting > Battery and Related Components"},
+    {"query": "check engine light misfire", "positive": "Ignition > Secondary Ignition", "negative": "Emission Control > Sensors"},
+    {"query": "ATF flush", "positive": "Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)", "negative": "Transmission > Automatic Transmission Components"},
+    {"query": "transmission fluid change", "positive": "Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)", "negative": "Transmission > Automatic Transmission Components"},
+    {"query": "Mailer oil change", "positive": "Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)", "negative": "Engine > Gaskets and Sealing Systems"},
+    {"query": "oil change special", "positive": "Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)", "negative": "Engine > Gaskets and Sealing Systems"},
+    {"query": "clunking over bumps", "positive": "Suspension > Shocks and Struts", "negative": "Brake > Drums and Rotors"},
+    {"query": "clunking over bumps", "positive": "Suspension > Shocks and Struts", "negative": "Driveline and Axles > CV Boots and Related Components"},
+    {"query": "noise over speed bumps", "positive": "Suspension > Shocks and Struts", "negative": "Transmission > Clutch Plates"},
+    {"query": "rotten egg smell", "positive": "Exhaust > Catalytic Converter", "negative": "Engine > Valve Train Components"},
+    {"query": "rotten egg smell", "positive": "Exhaust > Catalytic Converter", "negative": "Emission Control > Evaporative System"},
+    {"query": "sulfur smell exhaust", "positive": "Exhaust > Catalytic Converter", "negative": "Engine > Gaskets and Sealing Systems"},
+    {"query": "whining when turning", "positive": "Steering > Power Steering Hoses, Pumps, and Related Components", "negative": "Emission Control > Crankcase Ventilation System"},
+    {"query": "whining when turning", "positive": "Steering > Power Steering Hoses, Pumps, and Related Components", "negative": "Transmission > Flywheel"},
+    {"query": "whine turning wheel", "positive": "Steering > Power Steering Hoses, Pumps, and Related Components", "negative": "Emission Control > Sensors"},
+    {"query": "humming from wheel area", "positive": "Driveline and Axles > Wheel Bearings, Seals, and Related Components", "negative": "Tire and Wheel > Wheel"},
+    {"query": "humming from wheel area", "positive": "Driveline and Axles > Wheel Bearings, Seals, and Related Components", "negative": "Transmission > Flywheel"},
+    {"query": "humming gets louder with speed", "positive": "Driveline and Axles > Wheel Bearings, Seals, and Related Components", "negative": "Tire and Wheel > Sensors"},
+    {"query": "vehicle pulls right", "positive": "Suspension > Alignment", "negative": "Transmission > Flywheel"},
+    {"query": "vehicle pulls right", "positive": "Suspension > Alignment", "negative": "Driveline and Axles > Drive Shaft"},
+    {"query": "car drifts right", "positive": "Suspension > Alignment", "negative": "Steering > Steering Column"},
+    {"query": "mirror assembly", "positive": "Body > Mirrors", "negative": "Wiper and Washer > Windshield Washer and Related Components"},
+    {"query": "mirror assembly", "positive": "Body > Mirrors", "negative": "Wiper and Washer > Wiper Arm, Blade, and Related Components"},
+    {"query": "side mirror replacement", "positive": "Body > Mirrors", "negative": "Suspension > Alignment"},
+    {"query": "blower motor not working", "positive": "HVAC > Motors, Core, Case and Related Components", "negative": "Exhaust > Catalytic Converter"},
+    {"query": "blower motor not working", "positive": "HVAC > Motors, Core, Case and Related Components", "negative": "Emission Control > Crankcase Ventilation System"},
+    {"query": "no air from vents", "positive": "HVAC > Motors, Core, Case and Related Components", "negative": "Air and Fuel Delivery > Turbocharger, Supercharger and Ram Air"},
+    {"query": "upper mount plate", "positive": "Suspension > Shocks and Struts", "negative": "Transmission > Clutch Plates"},
+    {"query": "upper mount plate", "positive": "Suspension > Shocks and Struts", "negative": "Exhaust > Exhaust Manifolds"},
+    {"query": "strut mount plate", "positive": "Suspension > Shocks and Struts", "negative": "Suspension > Alignment"},
+    {"query": "control arm bushing worn", "positive": "Suspension > Suspension, Springs and Related Components", "negative": "Wiper and Washer > Wiper Arm, Blade, and Related Components"},
+    {"query": "control arm bushing worn", "positive": "Suspension > Suspension, Springs and Related Components", "negative": "Emission Control > Crankcase Ventilation System"},
+    {"query": "AC recharge needed blowing warm", "positive": "HVAC > A/C Clutch and Compressor", "negative": "Emission Control > Crankcase Ventilation System"},
+    {"query": "ac not blowing cold", "positive": "HVAC > A/C Clutch and Compressor", "negative": "Transmission > Radiators, Coolers and Related Components"},
+    {"query": "TPMS light on", "positive": "Tire and Wheel > Sensors", "negative": "Ignition > Distributor and Magneto"},
+    {"query": "TPMS light on", "positive": "Tire and Wheel > Sensors", "negative": "Driveline and Axles > CV Boots and Related Components"},
+    {"query": "tire pressure light on", "positive": "Tire and Wheel > Sensors", "negative": "Driveline and Axles > Wheel Bearings, Seals, and Related Components"},
+    # --- Expert-added hard negatives (with corrected PCAdb names) ---
+    {"query": "CEL rough running", "positive": "Ignition > Secondary Ignition", "negative": "Emission Control > Sensors"},
+    {"query": "CEL rough running", "positive": "Ignition > Secondary Ignition", "negative": "Engine > Valve Train Components"},
+    {"query": "CEL rough running", "positive": "Ignition > Secondary Ignition", "negative": "Air and Fuel Delivery > Fuel Pumps and Related Components"},
+    {"query": "CEL rough running", "positive": "Ignition > Secondary Ignition", "negative": "Air and Fuel Delivery > Filters"},
+    {"query": "Spark plugs replacement due", "positive": "Ignition > Secondary Ignition", "negative": "Ignition > Ignition Coil"},
+    {"query": "Spark plugs replacement due", "positive": "Ignition > Secondary Ignition", "negative": "Engine > Valve Train Components"},
+    {"query": "Spark plugs replacement due", "positive": "Ignition > Secondary Ignition", "negative": "Air and Fuel Delivery > Fuel Injection System and Related Components"},
+    {"query": "AC recharge needed", "positive": "HVAC > A/C Clutch and Compressor", "negative": "HVAC > A/C Condenser and Evaporator"},
+    {"query": "AC recharge needed", "positive": "HVAC > A/C Clutch and Compressor", "negative": "HVAC > Motors, Core, Case and Related Components"},
+    {"query": "blower not working", "positive": "HVAC > Motors, Core, Case and Related Components", "negative": "HVAC > A/C Clutch and Compressor"},
+    {"query": "blower not working", "positive": "HVAC > Motors, Core, Case and Related Components", "negative": "Belts and Cooling > Cooling Fan, Clutch and Motor"},
+    {"query": "TPMS light", "positive": "Tire and Wheel > Sensors", "negative": "Tire and Wheel > Tire"},
+    {"query": "timing chain needed", "positive": "Engine > Valve Train Components", "negative": "Belts and Cooling > Accessory Drive Belt System Components"},
+    {"query": "control arm bushing", "positive": "Suspension > Suspension, Springs and Related Components", "negative": "Suspension > Shocks and Struts"},
+    {"query": "control arm bushing", "positive": "Suspension > Suspension, Springs and Related Components", "negative": "Steering > Steering, Gear and Related Components"},
+    {"query": "clunking over bumps", "positive": "Suspension > Shocks and Struts", "negative": "Suspension > Suspension, Springs and Related Components"},
+    {"query": "clunking over bumps", "positive": "Suspension > Shocks and Struts", "negative": "Steering > Steering, Gear and Related Components"},
+    {"query": "clunking over bumps", "positive": "Suspension > Shocks and Struts", "negative": "Brake > Brake Hydraulics"},
+    {"query": "vehicle pulls right", "positive": "Suspension > Alignment", "negative": "Tire and Wheel > Tire"},
+    {"query": "vehicle pulls right", "positive": "Suspension > Alignment", "negative": "Brake > Brake Hydraulics"},
+    {"query": "vehicle pulls right", "positive": "Suspension > Alignment", "negative": "Suspension > Suspension, Springs and Related Components"},
+    {"query": "whining when turning", "positive": "Steering > Power Steering Hoses, Pumps, and Related Components", "negative": "Belts and Cooling > Accessory Drive Belt System Components"},
+    {"query": "whining when turning", "positive": "Steering > Power Steering Hoses, Pumps, and Related Components", "negative": "Driveline and Axles > CV Components"},
+    {"query": "humming from wheel area", "positive": "Driveline and Axles > Wheel Bearings, Seals, and Related Components", "negative": "Tire and Wheel > Tire"},
+    {"query": "humming from wheel area", "positive": "Driveline and Axles > Wheel Bearings, Seals, and Related Components", "negative": "Brake > Brake Hydraulics"},
+    {"query": "humming from wheel area", "positive": "Driveline and Axles > Wheel Bearings, Seals, and Related Components", "negative": "Driveline and Axles > Differential"},
+    # ====================== EXPANDED HARD NEGATIVES (v3+) ======================
+    # Catalytic converter — not engine, not evap, not fuel, not muffler
+    {"query": "rotten egg smell from exhaust", "positive": "Exhaust > Catalytic Converter", "negative": "Engine > Gaskets and Sealing Systems"},
+    {"query": "rotten egg smell from exhaust", "positive": "Exhaust > Catalytic Converter", "negative": "Air and Fuel Delivery > Fuel Pumps and Related Components"},
+    {"query": "sulfur smell", "positive": "Exhaust > Catalytic Converter", "negative": "Exhaust > Mufflers"},
+    {"query": "P0420 in memory", "positive": "Exhaust > Catalytic Converter", "negative": "Emission Control > Sensors"},
+    {"query": "cat code stored", "positive": "Exhaust > Catalytic Converter", "negative": "Emission Control > Evaporative System"},
+    {"query": "sounds like marbles in a can", "positive": "Exhaust > Catalytic Converter", "negative": "Engine > Valve Train Components"},
+    {"query": "honeycomb busted in cat", "positive": "Exhaust > Catalytic Converter", "negative": "Exhaust > Mufflers"},
+    {"query": "restricted exhaust", "positive": "Exhaust > Catalytic Converter", "negative": "Exhaust > Exhaust and Tail Pipes"},
+    # Starter — not battery, not alternator, not ignition
+    {"query": "car won't start, just clicks", "positive": "Electrical, Charging and Starting > Starter and Related Components", "negative": "Electrical, Charging and Starting > Battery and Related Components"},
+    {"query": "rapid clicking when turning key", "positive": "Electrical, Charging and Starting > Starter and Related Components", "negative": "Electrical, Charging and Starting > Alternator / Generator and Related Components"},
+    {"query": "tap starter and it starts", "positive": "Electrical, Charging and Starting > Starter and Related Components", "negative": "Ignition > Secondary Ignition"},
+    {"query": "hot soak no start", "positive": "Electrical, Charging and Starting > Starter and Related Components", "negative": "Air and Fuel Delivery > Fuel Pumps and Related Components"},
+    {"query": "nc/ns", "positive": "Electrical, Charging and Starting > Starter and Related Components", "negative": "Electrical, Charging and Starting > Battery and Related Components"},
+    # Ignition / CEL — not sensors, not fuel, not engine mechanical
+    {"query": "CEL on", "positive": "Ignition > Secondary Ignition", "negative": "Emission Control > Sensors"},
+    {"query": "runs like crap", "positive": "Ignition > Secondary Ignition", "negative": "Air and Fuel Delivery > Fuel Injection System and Related Components"},
+    {"query": "engine chugging", "positive": "Ignition > Secondary Ignition", "negative": "Engine > Valve Train Components"},
+    {"query": "coil pack bad", "positive": "Ignition > Secondary Ignition", "negative": "Electrical, Charging and Starting > Alternator / Generator and Related Components"},
+    {"query": "fouled plug", "positive": "Ignition > Secondary Ignition", "negative": "Air and Fuel Delivery > Filters"},
+    {"query": "it only does it when it rains", "positive": "Ignition > Secondary Ignition", "negative": "Belts and Cooling > Accessory Drive Belt System Components"},
+    # Overheating — not thermostat, not water pump (primary = radiator category)
+    {"query": "overheating", "positive": "Belts and Cooling > Radiators, Coolers and Related Components", "negative": "Belts and Cooling > Thermostat and Housing"},
+    {"query": "overheating", "positive": "Belts and Cooling > Radiators, Coolers and Related Components", "negative": "Belts and Cooling > Water Pump and Related Components"},
+    {"query": "temp pegged hot", "positive": "Belts and Cooling > Radiators, Coolers and Related Components", "negative": "Engine > Gaskets and Sealing Systems"},
+    {"query": "coolant leaking", "positive": "Belts and Cooling > Radiators, Coolers and Related Components", "negative": "Belts and Cooling > Hoses and Pipes"},
+    # Strut mounts — not control arms, not steering, not wheel bearings
+    {"query": "upper mount plate worn", "positive": "Suspension > Shocks and Struts", "negative": "Suspension > Suspension, Springs and Related Components"},
+    {"query": "strut mount bad", "positive": "Suspension > Shocks and Struts", "negative": "Steering > Steering, Gear and Related Components"},
+    {"query": "bearing plate bad", "positive": "Suspension > Shocks and Struts", "negative": "Driveline and Axles > Wheel Bearings, Seals, and Related Components"},
+    {"query": "mount collapsed", "positive": "Suspension > Shocks and Struts", "negative": "Engine > Engine and Transmission Mounts"},
+    {"query": "steering snaps back weird after turn", "positive": "Suspension > Shocks and Struts", "negative": "Steering > Power Steering Hoses, Pumps, and Related Components"},
+    # Turbo — not intake filters, not exhaust, not engine
+    {"query": "turbo boost leak", "positive": "Air and Fuel Delivery > Turbocharger, Supercharger and Ram Air", "negative": "Air and Fuel Delivery > Filters"},
+    {"query": "no boost", "positive": "Air and Fuel Delivery > Turbocharger, Supercharger and Ram Air", "negative": "Air and Fuel Delivery > Fuel Injection System and Related Components"},
+    {"query": "P0299", "positive": "Air and Fuel Delivery > Turbocharger, Supercharger and Ram Air", "negative": "Emission Control > Sensors"},
+    {"query": "turbo blown", "positive": "Air and Fuel Delivery > Turbocharger, Supercharger and Ram Air", "negative": "Engine > Valve Train Components"},
+    {"query": "whistles when I accelerate", "positive": "Air and Fuel Delivery > Turbocharger, Supercharger and Ram Air", "negative": "Belts and Cooling > Accessory Drive Belt System Components"},
+    {"query": "charge pipe blew off", "positive": "Air and Fuel Delivery > Turbocharger, Supercharger and Ram Air", "negative": "Belts and Cooling > Hoses and Pipes"},
+    # Alignment — not tire, not suspension components, not steering
+    {"query": "customer requests alignment check", "positive": "Suspension > Alignment", "negative": "Tire and Wheel > Tire"},
+    {"query": "customer requests alignment check", "positive": "Suspension > Alignment", "negative": "Steering > Steering, Gear and Related Components"},
+    {"query": "eating tires", "positive": "Suspension > Alignment", "negative": "Tire and Wheel > Tire"},
+    {"query": "dog tracking", "positive": "Suspension > Alignment", "negative": "Driveline and Axles > Drive Shaft"},
+    {"query": "needs front end lined up", "positive": "Suspension > Alignment", "negative": "Suspension > Suspension, Springs and Related Components"},
+    # Oil change / mailer — not engine, not filters
+    {"query": "came in with mailer for oil change", "positive": "Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)", "negative": "Engine > Gaskets and Sealing Systems"},
+    {"query": "LOF", "positive": "Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)", "negative": "Engine > Filters"},
+    {"query": "maintenance light on for oil", "positive": "Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)", "negative": "Electrical, Charging and Starting > Battery and Related Components"},
+    {"query": "oil life says 15%", "positive": "Oil, Fluids and Chemicals > Functional Fluid, Lubricant, Grease (including Additives)", "negative": "Engine > Cylinder Block Components"},
+    # Bonus cross-category disambiguation
+    {"query": "smells like syrup in the car", "positive": "HVAC > Air Heater Components", "negative": "Exhaust > Catalytic Converter"},
+    {"query": "all the lights came on and steering got hard", "positive": "Belts and Cooling > Accessory Drive Belt System Components", "negative": "Steering > Power Steering Hoses, Pumps, and Related Components"},
+    {"query": "battery keeps dying overnight", "positive": "Electrical, Charging and Starting > Battery and Related Components", "negative": "Electrical, Charging and Starting > Alternator / Generator and Related Components"},
+    {"query": "brake pedal goes to floor", "positive": "Brake > Brake Hydraulics", "negative": "Brake > Disc Pads and Brake Shoes"},
+    {"query": "gas smell after I fill up", "positive": "Emission Control > Evaporative System", "negative": "Air and Fuel Delivery > Fuel Pumps and Related Components"},
+    {"query": "clicking in dash", "positive": "HVAC > Motors, Core, Case and Related Components", "negative": "Electrical, Charging and Starting > Starter and Related Components"},
+    {"query": "thumps when I stop", "positive": "Engine > Engine and Transmission Mounts", "negative": "Suspension > Shocks and Struts"},
+    {"query": "car leans on one side", "positive": "Suspension > Suspension, Springs and Related Components", "negative": "Suspension > Alignment"},
+    {"query": "sounds like an airplane on the highway", "positive": "Driveline and Axles > Wheel Bearings, Seals, and Related Components", "negative": "Tire and Wheel > Tire"},
+    {"query": "won't go over 20 mph", "positive": "Air and Fuel Delivery > Fuel Injection System and Related Components", "negative": "Transmission > Automatic Transmission Components"},
+]
+
+
+# ============================================================================
+# DATA GENERATION
+# ============================================================================
+
+def apply_typo(text: str) -> str | None:
+    lower = text.lower()
+    for correct, typos in COMMON_TYPOS.items():
+        if correct in lower:
+            typo = random.choice(typos)
+            return text.replace(correct, typo).replace(correct.capitalize(), typo.capitalize())
+    return None
+
+
+def generate_training_data() -> tuple[list[dict], list[dict]]:
+    """Generate training pairs and triplets. Returns (positive_pairs, triplets)."""
+    qp = "Represent this sentence for searching relevant passages: "
+    dp = ""
+    positive_pairs = []
+    triplets = []
+
+    # Source 1: keyword → subcategory with variant templates
+    for entry in KEYWORD_TO_SUBCATEGORIES:
+        for kw in entry["keywords"]:
+            for subcat in entry["subcategories"]:
+                for tmpl in VARIANT_TEMPLATES:
+                    query = tmpl.format(kw=kw)
+                    positive_pairs.append({"query": f"{qp}{query}", "positive": f"{dp}{subcat}"})
+                typo_text = apply_typo(f"Replace {kw}")
+                if typo_text:
+                    positive_pairs.append({"query": f"{qp}{typo_text}", "positive": f"{dp}{subcat}"})
+
+    # Source 2: symptom-based with template expansion
+    for entry in SYMPTOM_VARIANTS:
+        for symptom in entry["symptoms"]:
+            for subcat in entry["subcategories"]:
+                for tmpl in SYMPTOM_TEMPLATES:
+                    query = tmpl.format(symptom=symptom)
+                    positive_pairs.append({"query": f"{qp}{query}", "positive": f"{dp}{subcat}"})
+
+    # Source 3: hard negatives (triplets)
+    for hn in HARD_NEGATIVES:
+        triplets.append({
+            "query": f"{qp}{hn['query']}",
+            "positive": f"{dp}{hn['positive']}",
+            "negative": f"{dp}{hn['negative']}",
+        })
+
+    random.shuffle(positive_pairs)
+    random.shuffle(triplets)
+    return positive_pairs, triplets
+
+
+# ============================================================================
+# EVALUATION — DO NOT MODIFY
+# ============================================================================
+
+def strip_prefix(text: str) -> str:
+    for prefix in ("Represent this sentence for searching relevant passages: ", "search_query: ", "search_document: "):
+        if text.startswith(prefix):
+            return text[len(prefix):]
+    return text
+
+
+def evaluate_model(model: SentenceTransformer, corpus_names: list[str]) -> dict:
+    """Run benchmark evaluation. Returns metrics dict."""
+    k_values = [1, 3, 5, 10]
+
+    # BGE: no prefix for documents
+    corpus_texts = [name for name in corpus_names]
+    corpus_embeddings = model.encode(corpus_texts, normalize_embeddings=True, show_progress_bar=False)
+
+    # BGE: instruction prefix for queries
+    query_texts = [f"Represent this sentence for searching relevant passages: {b['concern']}" for b in BENCHMARK]
+    query_embeddings = model.encode(query_texts, normalize_embeddings=True, show_progress_bar=False)
+
+    sim_matrix = np.array(query_embeddings) @ np.array(corpus_embeddings).T
+
+    hits_at_k = {k: 0 for k in k_values}
+    failures = []
+    garbage_correct = 0
+    garbage_total = 0
+
+    for i, case in enumerate(BENCHMARK):
+        expected = set(case["expected_subcategories"])
+        scores = sim_matrix[i]
+        ranked_indices = np.argsort(scores)[::-1]
+
+        if len(expected) == 0:
+            garbage_total += 1
+            top_score = scores[ranked_indices[0]]
+            if top_score < GARBAGE_THRESHOLD:
+                garbage_correct += 1
+            continue
+
+        for k in k_values:
+            top_k_names = {corpus_names[idx] for idx in ranked_indices[:k]}
+            if expected & top_k_names:
+                hits_at_k[k] += 1
+
+        top_5_names = [corpus_names[idx] for idx in ranked_indices[:5]]
+        if not (expected & set(top_5_names)):
+            failures.append(case["concern"])
+
+    n_real = sum(1 for c in BENCHMARK if len(c["expected_subcategories"]) > 0)
+    accuracy = {k: hits_at_k[k] / n_real * 100 for k in k_values}
+
+    return {
+        "hit_at_1": accuracy[1],
+        "hit_at_5": accuracy[5],
+        "hit_at_10": accuracy[10],
+        "garbage_correct": garbage_correct,
+        "garbage_total": garbage_total,
+        "failures": failures,
+        "n_real": n_real,
+    }
+
+
+# ============================================================================
+# TRAINING
+# ============================================================================
+
+def train():
+    import torch
+    print(f"=== Automotive Embedding Fine-Tuning ===")
+    print(f"CUDA available: {torch.cuda.is_available()}")
+    if torch.cuda.is_available():
+        print(f"GPU: {torch.cuda.get_device_name(0)}")
+    print(f"Base model: {BASE_MODEL}")
+    print(f"Epochs: {EPOCHS}, Batch size: {BATCH_SIZE}, LR: {LEARNING_RATE}")
+    print(f"Matryoshka dims: {MATRYOSHKA_DIMS}")
+    print()
+
+    # Generate data
+    print("Generating training data...")
+    positive_pairs, triplets = generate_training_data()
+    print(f"  Positive pairs: {len(positive_pairs)}")
+    print(f"  Hard negative triplets: {len(triplets)}")
+
+    # Build corpus for evaluation
+    all_subcats = set()
+    for p in positive_pairs:
+        all_subcats.add(strip_prefix(p["positive"]))
+    for t in triplets:
+        all_subcats.add(strip_prefix(t["positive"]))
+        all_subcats.add(strip_prefix(t["negative"]))
+    corpus_names = sorted(all_subcats)
+    print(f"  Corpus size: {len(corpus_names)} subcategories")
+
+    # Load model
+    print(f"\nLoading {BASE_MODEL}...")
+    model = SentenceTransformer(BASE_MODEL)
+
+    # Baseline evaluation
+    print("\n--- Baseline (before training) ---")
+    baseline = evaluate_model(model, corpus_names)
+    print(f"  Hit@1={baseline['hit_at_1']:.1f}%  Hit@5={baseline['hit_at_5']:.1f}%  Hit@10={baseline['hit_at_10']:.1f}%")
+    print(f"  Garbage: {baseline['garbage_correct']}/{baseline['garbage_total']}")
+    if baseline["failures"]:
+        print(f"  Failures ({len(baseline['failures'])}): {baseline['failures']}")
+
+    # Build training objectives — MNRL (no Matryoshka) + hard negative TripletLoss
+    pos_examples = [InputExample(texts=[p["query"], p["positive"]]) for p in positive_pairs]
+    trip_examples = [InputExample(texts=[t["query"], t["positive"], t["negative"]]) for t in triplets]
+
+    train_objectives = []
+
+    if pos_examples:
+        pos_loader = DataLoader(pos_examples, shuffle=True, batch_size=BATCH_SIZE)
+        mnrl_loss = losses.MultipleNegativesRankingLoss(model)
+        if MATRYOSHKA_DIMS:
+            mnrl_loss = losses.MatryoshkaLoss(model, mnrl_loss, matryoshka_dims=MATRYOSHKA_DIMS)
+        train_objectives.append((pos_loader, mnrl_loss))
+
+    if trip_examples:
+        trip_loader = DataLoader(trip_examples, shuffle=True, batch_size=BATCH_SIZE)
+        triplet_loss = losses.TripletLoss(model)
+        if MATRYOSHKA_DIMS:
+            triplet_loss = losses.MatryoshkaLoss(model, triplet_loss, matryoshka_dims=MATRYOSHKA_DIMS)
+        train_objectives.append((trip_loader, triplet_loss))
+
+    total_steps = sum(len(loader) for loader, _ in train_objectives) * EPOCHS
+    warmup_steps = int(total_steps * WARMUP_RATIO)
+
+    # Train to a temp directory
+    output_dir = tempfile.mkdtemp(prefix="automotive-embed-")
+    print(f"\nTraining ({total_steps} steps, {warmup_steps} warmup)...")
+
+    model.fit(
+        train_objectives=train_objectives,
+        epochs=EPOCHS,
+        warmup_steps=warmup_steps,
+        optimizer_params={"lr": LEARNING_RATE},
+        output_path=output_dir,
+        show_progress_bar=True,
+    )
+
+    # Evaluate the in-memory trained model directly
+    # (Reloading from disk causes _IncompatibleKeys with nomic's custom architecture)
+    print("\n--- Fine-tuned (after training) ---")
+    result = evaluate_model(model, corpus_names)
+    print(f"  Hit@1={result['hit_at_1']:.1f}%  Hit@5={result['hit_at_5']:.1f}%  Hit@10={result['hit_at_10']:.1f}%")
+    print(f"  Garbage: {result['garbage_correct']}/{result['garbage_total']}")
+    if result["failures"]:
+        print(f"  Failures ({len(result['failures'])}): {result['failures']}")
+
+    # Delta
+    d1 = result["hit_at_1"] - baseline["hit_at_1"]
+    d5 = result["hit_at_5"] - baseline["hit_at_5"]
+    d10 = result["hit_at_10"] - baseline["hit_at_10"]
+    print(f"\n--- Delta ---")
+    print(f"  Hit@1: {'+' if d1 >= 0 else ''}{d1:.1f}%  Hit@5: {'+' if d5 >= 0 else ''}{d5:.1f}%  Hit@10: {'+' if d10 >= 0 else ''}{d10:.1f}%")
+
+    # Parseable result line
+    print(f"\nRESULT: hit@1={result['hit_at_1']:.1f} hit@5={result['hit_at_5']:.1f} hit@10={result['hit_at_10']:.1f} garbage={result['garbage_correct']}/{result['garbage_total']}")
+
+    # Save model path
+    print(f"\nModel saved to: {output_dir}")
+
+    return result
+
+
+if __name__ == "__main__":
+    train()