Each case study below contains Decision Points (DP) — documented moments where analysis shaped the system direction. Methodology tags (E-178, E-188, SSM, VSM) trace each decision to its engineering framework.
n8n self-hosted · Claude API · Custom NestJS backend · Supabase
Context: Client needed automated content aggregation from 7 sources. Off-the-shelf SaaS tools (Feedly, Zapier) priced per-seat, per-connection.
Analysis (E-188): Projected 12-month total cost of ownership. SaaS stack: ~USD 800/mo at required volume. Self-hosted n8n + Claude API: ~USD 150/mo. Break-even at month 2.
Decision: Self-hosted. Accepted higher initial build effort for lower marginal cost and full architectural control.
Context: Client's content team needed actionable intelligence, not summaries. Original requirement was "summarize articles."
Analysis (E-178): Requirements elicitation revealed the actual need: structured data fields (brand mentioned, sentiment, product category, competitive signal) for filtering and decision-making.
Decision: Designed Claude API prompts for structured JSON extraction with defined schema, not freeform summaries. This enabled dashboard filtering and trend analysis that summaries couldn't support.
Context: Content monitoring doesn't require sub-minute latency. Most sources update hourly at most.
Analysis (E-178): Real-time webhooks add complexity (webhook management, retry logic, connection state) for no user-perceptible benefit. 15-minute polling matches source update frequency.
Decision: Batch polling on 15-min cron. Simpler failure modes, predictable resource usage, easier debugging. Added dead-letter queue for failed extractions.
Next.js · Supabase · SHA-256 hash chain · Stripe billing
Context: Contract agreements need tamper evidence. Simple audit logs (timestamp + user) can be modified without detection.
Analysis (E-178): SHA-256 hash chain where each entry's hash includes the previous entry's hash. Any modification to historical records breaks the chain. Verification is O(n) scan — acceptable for contract volumes.
Decision: Implemented hash chain with Supabase RLS enforcing append-only at the database level. No application code can UPDATE or DELETE agreement records.
Context: When users cancel their Stripe subscription, their existing agreements still have legal value. Deleting data or blocking access entirely creates liability.
Analysis (E-188): Risk assessment of three options: (1) full lockout — legal risk, (2) continued full access — no revenue incentive, (3) read-only mode — preserves data access, incentivizes resubscription.
Decision: Implemented tiered access: active subscription = full read/write, cancelled = read-only with export capability. Stripe webhook handles state transitions.
SSM (Checkland) · VSM (Beer) · Nudge Architecture (Thaler/Sunstein) · Python + FastAPI
Context: AU market entry required understanding regulatory environment, competitive landscape, and user behavior patterns simultaneously.
Analysis: SSM (Checkland) for problem structuring — rich pictures and root definitions to map stakeholder perspectives. VSM (Beer) for viability diagnosis — identifying regulatory constraints and required variety. Nudge (Thaler/Sunstein) for choice architecture — designing defaults and decision flows.
Decision: Three-layer methodology stack: SSM defines the problem space, VSM validates system viability, Nudge shapes the user-facing implementation. Each layer's output feeds the next.
Context: New market, uncertain demand. Full specification upfront risks building the wrong thing.
Analysis (E-188): Engineering economics: cost of change increases exponentially with project phase (E-178 principle). But cost of building the wrong product is total loss. In high-uncertainty environments, information has option value — each iteration buys knowledge.
Decision: Phased delivery: SSM-validated MVP first, then VSM-guided scaling. Each phase gated by measurable criteria, not timeline. Delivered within 3 months from design to deployment.
| Claim | Method | Evidence |
|---|---|---|
| Full lifecycle delivery | V-Model (E-178) | CS1: requirements → build → 99%+ uptime operation |
| Cost-conscious architecture | Eng. Economics (E-188) | CS1 DP-1: TCO analysis, break-even month 2 |
| Requirements analysis | SE Process (E-178) | CS1 DP-2: elicitation changed output from summaries to structured extraction |
| Security-first design | SE Process (E-178) | CS2 DP-4: SHA-256 hash chain + RLS append-only |
| Risk quantification | Decision Quality (E-188) | CS2 DP-5: three-option risk assessment for subscription cancellation |
| Systems thinking methodology | SSM + VSM | CS3 DP-6: three-layer methodology (SSM → VSM → Nudge) |
| Engineering economics | Eng. Economics (E-188) | CS3 DP-7: option value analysis for phased delivery |
| Autonomous operation | V-Model (E-178) | CS1: 99%+ uptime, single operator, 15-min batch cycle |