UX: Insights tab shows per-cable weight, users expect total weight

[9thLevelSoftware]

Problem

The Insights tab (plateau detection, volume metrics) displays weight values per-cable (e.g., "5kg"), but users think in terms of total weight (what the Vitruvian machine's display shows, e.g., "10kg"). This creates confusion — particularly in the plateau detection card where "Bench Press at 5kg" looks wrong to a user who set the machine to 10kg.

The portal already handles this correctly by multiplying per-cable values by 2 (WEIGHT_MULTIPLIER = 2 in src/schemas/transforms.ts). The mobile app's Insights tab does not.

Context (from monorepo CLAUDE.md)

All weight values in the database are per-cable (single cable, 0-220kg range)
Portal multiplies by 2 for display

Scope

This affects multiple display surfaces in the mobile app, not just Insights:

• PlateauDetectionCard — shows per-cable weight
• WeeklyVolumeCard — volume computed from per-cable values
• SetSummaryCard — displays per-cable weight as "Weight"
• History cards — show per-cable weight

Proposed Approach

1. Add a weight display utility that accounts for cable count:

   fun displayWeight(perCableKg: Float, cableCount: Int = 2): Float = perCableKg * cableCount

2. Apply to all user-facing weight displays in the Insights tab, set summary, and history
3. Keep database values per-cable — only transform at the display layer
4. Respect the user's weight unit preference (kg vs lbs) in the same utility
5. Handle single-cable exercises — use cableCount = 1 from the session's cableCount field

Risk

This is a cross-cutting display change. Must ensure consistency across ALL weight displays and avoid double-multiplying. The cableCount field is nullable (NULL for legacy sessions) — default to 2 for backward compatibility.

Found during investigation of #318.

[9thLevelSoftware]

✅ Implemented in v0.9.0

What Changed

Weight display is now equipment-aware. The app differentiates between exercises using a unified attachment (long bar, belt) versus individual handles on separate cables.

• Unified attachments (BAR, BELT): Weight shows as combined total (e.g., 25kg/cable → displays 50 kg)
• Individual attachments (HANDLES, ROPE, SHORT_BAR, STRAPS): Weight shows per-cable (e.g., 25kg/cable → displays 25 kg)

This applies to all weight display surfaces: Set Summary card, History tab, Home screen, Exercise Detail, Workout HUD, Analytics, Dashboard PRs, and the active workout PR celebration overlay.

A new WeightDisplayFormatter utility centralizes all cable-aware weight conversion, and a display_multiplier column on WorkoutSession persists the correct multiplier per session for historical accuracy.

How to Access

No action needed — weight values automatically display correctly based on the exercise's equipment configuration. The exercise library metadata determines whether an exercise uses a bar/belt (combined weight) or individual handles (per-cable weight).

Technical Details

• Exercise.displayMultiplier property: returns 2 only for DUAL cable intent + BAR/BELT equipment
• cableCount field preserved unchanged for volume/telemetry calculations
• Legacy sessions use fallback chain: displayMultiplier → cableCount → 1
• Database migration 29 adds display_multiplier column to WorkoutSession

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This enhancement is implemented on branch feat/v0.9.0-enhancement-sweep and will be included in the next version release.

[9thLevelSoftware]

Closing as implemented in v0.9.0 Enhancement Sweep. See comment above for details and usage instructions.