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Notes from the systems I build

Business owner guides in Arabic: دليل صاحب الشركة

Building a CRM for an installation business

A build log of the CRM behind ZS Tech, a smart home and access control company in Cairo: quotes, cost hiding, money, permissions, and tests.

2 Oct 2026 · 6 min readBuilding a CRM for an installation business · Part 1

Modelling quotes for a business that installs things

How I modelled quotes for a smart home installer: a price book with supplier costs, packages, quote sections, and costs that freeze when a deal is won.

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2 Oct 2026 · 5 min readBuilding a CRM for an installation business · Part 2

Hiding cost and margin in Postgres, not in the UI

Field staff need the quote, not the margin. How column grants and gated views keep cost out of every API response, and the bug that taught me a rule.

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More notes

14 Sept 2026 · 3 min read

Multi-tenant SaaS on Supabase: isolating tenants with Row-Level Security

How Hodori keeps every school's data isolated on one PostgreSQL database: a denormalised organisation id on every table, RLS policies that read the JWT, business logic in SECURITY DEFINER RPCs, and the super-admin trap I had to close.

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14 Sept 2026 · 2 min read

Egyptian e-invoicing (ETA) inside a custom ERP: what the integration actually needs

Lessons from wiring Egyptian Tax Authority e-invoice submissions into a custom ERP: model submissions as their own table, treat VAT registration as data not code, and keep the money views honest.

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14 Sept 2026 · 3 min read

WhatsApp Business API: delivery tracking, tier pacing, and the 24-hour window, done properly

What it took to send event invitations to hundreds of guests on the Meta Cloud API from inside a CRM: a rank-guarded status machine, one worker holding credentials, a drain loop for the messaging tier, and a quality circuit breaker.

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14 Sept 2026 · 1 min read

Splitting a port logistics platform into eight micro-frontends without splitting the design

How the SCR (Secure Container Release) web platform at T-Mining was restructured into eight independently deployable frontend modules with one shared component library, and what a 60% load-time improvement actually required.

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