Index: docs/P3-UseCaseModel/UseCaseModel.md
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--- docs/P3-UseCaseModel/UseCaseModel.md	(revision b715712c7d5d3ee27c932a8a9d8e0a2bc6e85127)
+++ docs/P3-UseCaseModel/UseCaseModel.md	(revision df058387ebe7d07864d874fd1376f15512418581)
@@ -1,34 +1,113 @@
-# Use-case model
+= Use-case model =
 
-## List of Actors / Roles
+The detailed pages for this phase are kept in the project's GitHub repository,
+[https://github.com/StefanTrsunov/bp StefanTrsunov/bp], under `docs/P3-UseCaseModel/`. Every
+use-case link below opens the corresponding file there.
 
-- **Visitor** — Anyone browsing the platform without an account. Can only view public market information.
-  - [UC0001](UseCase0001.md) — Register new account
-  - [UC0002](UseCase0002.md) — Log in
+== Actors / Roles ==
 
-- **Trader** — A logged-in user managing their virtual funds and positions.
-  - [UC0003](UseCase0003.md) — Deposit virtual funds
-  - [UC0004](UseCase0004.md) — Place market BUY order
-  - [UC0005](UseCase0005.md) — Place market SELL order
-  - [UC0006](UseCase0006.md) — View portfolio and transaction history
-  - [UC0007](UseCase0007.md) — Manage watchlist
+'''Visitor''' – Anyone using EduBerza without an account, who can look at public market
+information, create an account, and log in.
 
-- **Market Simulator** — An external automated system (the bot in `bots/`) that inserts simulated trades and candles into the database so prices move in the simulation.
+'''Trader''' – A registered, logged-in user who deposits virtual funds, places market buy and
+sell orders, follows the value of their portfolio, and keeps a watchlist of assets they want to
+monitor.
 
-## Use-case model diagram (optional)
+'''Market Simulator''' – An external automated system (the bot in `bots/`) that writes simulated
+trades and candles into the database so prices move without a connection to a real exchange.
 
-*(Optional per the rubric; include one later if time allows.)*
+== Use-Cases ==
 
-## Realization details on selection of the most important use cases
+=== Visitor ===
 
-Solo project → **at least 3 use cases required** (rubric: "at least 3 per team-member"). **7 use cases documented** for a safety margin. All are implemented in the P4 prototype; see `server/` for the Go source and [PrototypeImplementation](../P4-Prototype/PrototypeImplementation.md) for documented runs.
+ * [https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0001.md UC0001] –
+   '''Register new account''' – Visitor creates an account with a unique username and e-mail; the
+   password is stored as a SHA-256 hash.
+ * [https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0002.md UC0002] –
+   '''Log in''' – Visitor authenticates with username and password so the system treats every
+   following action as a Trader.
 
-| Use case                               | Importance | Why documented                                                                            |
-|----------------------------------------|------------|-------------------------------------------------------------------------------------------|
-| [UC0001 — Register](UseCase0001.md)    | High       | Without it nothing else works; demonstrates `INSERT` with uniqueness check.               |
-| [UC0002 — Login](UseCase0002.md)       | High       | Authenticates every `Trader` action; demonstrates `SELECT` with parameter binding.        |
-| [UC0003 — Deposit](UseCase0003.md)     | High       | Shows a multi-row transaction: `UPDATE users` + `INSERT INTO transactions`.               |
-| [UC0004 — Buy](UseCase0004.md)         | Very high  | Core of the exchange: `INSERT orders`, `UPDATE users`, `UPSERT holdings`, ledger, trade.  |
-| [UC0005 — Sell](UseCase0005.md)        | Very high  | Dual of Buy; demonstrates row-level `FOR UPDATE` locking and cost-basis bookkeeping.      |
-| [UC0006 — Portfolio](UseCase0006.md)   | High       | Demonstrates joins over `holdings`, `markets`, `crypto`, and a view (`v_portfolio`).      |
-| [UC0007 — Watchlist](UseCase0007.md)   | Medium     | Demonstrates N-M relation handling and `ON CONFLICT` upsert semantics.                    |
+=== Trader ===
+
+ * [https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0003.md UC0003] –
+   '''Deposit virtual funds''' – Trader tops up their virtual cash balance; the user row and the
+   ledger are written in one transaction.
+ * [https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0004.md UC0004] –
+   '''Place market BUY order''' – Trader buys a crypto asset at the current market price, which
+   debits cash and upserts the holding at a running weighted-average price.
+ * [https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0005.md UC0005] –
+   '''Place market SELL order''' – Trader sells part or all of a holding at the current market
+   price, which credits cash and preserves the cost basis.
+ * [https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0006.md UC0006] –
+   '''View portfolio and transaction history''' – Trader inspects current holdings, unrealised
+   P/L, cash balances and the most recent ledger entries.
+ * [https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0007.md UC0007] –
+   '''Manage watchlist''' – Trader lists, adds and removes crypto assets on a personal watchlist,
+   where adding an asset already on the list is a no-op.
+
+=== Market Simulator ===
+
+The Market Simulator initiates no use case of its own. It participates in
+[https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0004.md UC0004] and
+[https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0005.md UC0005]
+indirectly, by keeping `project.market_trades` populated so that `project.v_latest_prices`
+returns a current price for every active market.
+
+== Use-case model diagram ==
+
+{{{#!comment
+The diagram is optional for P3. Commit the exported image to
+docs/P3-UseCaseModel/use_case_diagram.png and then replace this comment with:
+
+[https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/use_case_diagram.png Use-case model diagram]
+}}}
+
+== Detailed Use-Cases ==
+
+The following use-cases are documented in detail, with SQL tested against the P2 database:
+
+ * [https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0001.md UseCase0001] – Visitor registers a new account
+ * [https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0002.md UseCase0002] – Visitor logs in
+ * [https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0003.md UseCase0003] – Trader deposits virtual funds
+ * [https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0004.md UseCase0004] – Trader places a market BUY order
+ * [https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0005.md UseCase0005] – Trader places a market SELL order
+ * [https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0006.md UseCase0006] – Trader views portfolio and transaction history
+ * [https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0007.md UseCase0007] – Trader manages a watchlist
+
+== Realization details on selection of the most important use cases ==
+
+This is a solo project, so '''at least 3 use cases''' are required. '''7 use cases''' are
+documented, for a safety margin. All seven are implemented in the P4 prototype; see
+[https://github.com/StefanTrsunov/bp/tree/main/server server/] for the Go source and
+[https://github.com/StefanTrsunov/bp/blob/main/docs/P4-Prototype/PrototypeImplementation.md PrototypeImplementation]
+for the documented runs.
+
+||=Use case=||=Importance=||=Why it was selected=||
+||[https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0001.md UC0001 – Register]||High||Nothing else works without it; demonstrates `INSERT` with a uniqueness check.||
+||[https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0002.md UC0002 – Log in]||High||Authenticates every Trader action; demonstrates `SELECT` with parameter binding.||
+||[https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0003.md UC0003 – Deposit]||High||Shows a multi-row transaction: `UPDATE users` plus `INSERT INTO transactions`.||
+||[https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0004.md UC0004 – Buy]||Very high||Core of the exchange: `INSERT orders`, `UPDATE users`, upsert `holdings`, ledger entry, market trade.||
+||[https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0005.md UC0005 – Sell]||Very high||Dual of Buy; demonstrates row-level `FOR UPDATE` locking and cost-basis bookkeeping.||
+||[https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0006.md UC0006 – Portfolio]||High||Demonstrates joins over `holdings`, `markets` and `crypto`, and the `v_portfolio` view.||
+||[https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCase0007.md UC0007 – Watchlist]||Medium||Demonstrates N–M relation handling and `ON CONFLICT` upsert semantics.||
+
+== AI usage ==
+
+AI was used in this phase and is logged in full, per the course rule for P1 onward.
+
+ * '''Phase log:'''
+   [https://github.com/StefanTrsunov/bp/blob/main/docs/P3-UseCaseModel/UseCaseModelAIUsage.md UseCaseModelAIUsage.md]
+   – service used, what the AI produced, and what I decided myself.
+ * '''Full conversation transcript:'''
+   [https://github.com/StefanTrsunov/bp/blob/main/docs/P1-ConceptualModel/ERModelAIUsage.md ERModelAIUsage.md]
+   – the same conversation produced the P1–P4 artefacts, so the complete prompt/response log is
+   kept in one place. Direct links:
+   [https://github.com/StefanTrsunov/bp/blob/main/docs/P1-ConceptualModel/ERModelAIUsage.md#session-1--2026-04-21 Session 1 – 2026-04-21],
+   [https://github.com/StefanTrsunov/bp/blob/main/docs/P1-ConceptualModel/ERModelAIUsage.md#session-2--2026-08-06--2026-08-07 Session 2 – 2026-08-06/07].
+
+'''Service:''' Claude Code (Anthropic), https://claude.com/claude-code – Claude subscription,
+model Claude Opus 4.7 (1M context).
+
+'''In short:''' the AI proposed the actor taxonomy and drafted the seven use cases with their SQL
+in session 1. In session 2 the use-case model itself was '''not''' changed – the only work was
+re-executing every scenario, including the failure paths, against a live PostgreSQL 16 database.