[P1] Attribute provider usage and COGS by user, feature, and plan

[postigodev]

Context

Preppie cannot safely choose permanent pricing from flat per-user assumptions. OpenAI, ElevenLabs, vision, infrastructure, storage, and payment processing have different cost drivers. Voice duration is currently the largest unknown and may determine whether a $6.99/month plan is viable.

The product needs cost attribution that is operationally useful without retaining private prompts, transcripts, images, or recipe content.

Scope

Provider usage capture

• Capture request counts, token/input/output usage, image usage, model/provider, latency, success/failure, and provider-reported cost fields where available for OpenAI operations.
• Capture voice session start/end, connected duration, provider-billed duration/credits, silence discount where exposed, reconnects, model/provider, and outcome for ElevenLabs.
• Capture vision CPU/GPU duration, request size, result count, and provider/infrastructure allocation where meaningful.
• Capture external retailer/product-provider calls that have rate or financial implications.
• Capture Stripe processing and Billing fees from settled transaction/invoice data rather than one flat percentage.

Cost model

• Maintain versioned provider price tables with currency, unit, effective date, source URL, and verification date.
• Calculate estimated cost per event using the applicable price version.
• Reconcile estimates against actual provider invoices or dashboard exports monthly.
• Separate variable provider COGS from shared fixed infrastructure allocation.
• Preserve raw provider usage quantities so past periods can be recalculated if the cost formula was wrong.

Product reporting

Provide views for:

• Cost per active free user, paid user, and voice-active user.
• Cost per feature/category.
• Cost and contribution margin by plan and cohort.
• Heavy-user distribution and p50/p90/p95 usage.
• Voice connected minutes versus provider-billed minutes.
• Free-to-paid subsidy and trial cost.
• Revenue, refunds, fees, net revenue, variable COGS, and contribution margin.

Guardrails

• Add alerts for abnormal token use, long/repeated voice sessions, reconnect loops, provider price changes, invoice variance, and plan-level negative margin.
• Support provider and application spend caps where available.
• Define a monthly pricing review using measured data from this issue and the source register.

Privacy

• Do not persist raw prompts, transcripts, audio, images, recipes, or pantry contents solely for cost analytics.
• Use opaque user/account references and sanitized feature metadata.
• Define retention and aggregation policy for detailed events.

Acceptance criteria

• OpenAI and ElevenLabs usage can be attributed to user, plan, feature, and billing period without storing content.
• Voice reports distinguish connected duration from provider-billed duration where the provider exposes both.
• Stripe fees use settled transaction/invoice evidence rather than a fixed modeled percentage.
• Provider price tables are versioned and source-linked.
• Estimated monthly provider cost is reconciled against actual invoices/dashboard totals.
• Contribution margin is visible by plan and usage cohort.
• Alerts detect reconnect loops, extreme users, cost spikes, and materially negative plan margin.
• Pricing decisions can be made using at least two complete billing cycles of measured data.

Dependencies

• Usage ledger and entitlements: [P0] Define plan entitlements and durable usage accounting #119.
• Billing lifecycle: [P0] Build Stripe subscription billing and customer lifecycle #118.
• Voice transport and teardown: [P0] Enforce real hands-free audio gating and accurate microphone states #111.
• Cross-service/frontend observability: [P1] Add cross-service, frontend, and database observability #95.
• Provider minimization and retention: [P0] Minimize AI provider data and verify retention controls #101 and [P1] Define retention and real deletion for operational user data, media, and logs #102.
• Pricing/source register: follow-up issue.

Out of scope

• Full corporate accounting or GAAP revenue recognition.
• Storing private content for analytics convenience.
• Automatically changing customer pricing without human approval.