= Use-Case Model AI Usage =

== Name of AI service/solution that was used ==

'''Claude Code''' (Anthropic)

 * '''URL:''' `https://claude.com/claude-code`
 * '''Type of service/subscription:''' Claude subscription, model Claude Opus 4.7 (1M context).

== Final result ==

=== Results in details / description ===

The AI:

 * Proposed the actor taxonomy (Visitor, Trader, Market Simulator) from the project description and the existing Go code.
 * Derived a set of 7 use cases covering the full trading loop (register, login, deposit, buy, sell, view portfolio, watchlist).
 * Wrote each `UseCaseXXXX.md` file with:
   * initiating actor, other actors, goals
   * step-by-step dialog-form scenario
   * '''tested''' SQL statements for every database-touching step, using the `project` schema
   * alternate flows for the most common failure cases (insufficient funds, insufficient holding, duplicate user, invalid input)

== Summary of AI involvement ==

||= =||= Session 1 — 2026-04-21 =||= Session 2 — 2026-08-06/07 =||
|| '''What I brought''' || The project description in `opis.md` and the existing Go backend || The use-case model as completed in session 1 ||
|| '''What the AI did''' || Proposed the actor taxonomy and drafted seven use cases with tested SQL || Nothing — the model was not changed ||
|| '''What I decided''' || To go solo, and therefore to document seven use cases rather than the three the rubric requires || To re-verify every scenario's SQL against a live database rather than trust the April run ||

This phase was finished in session 1. In session 2 the only work was
verification: each scenario was executed against a live PostgreSQL 16 database,
including the failure paths, and the results recorded on the
`UseCaseXXXXImplementation` pages.

== Entire AI usage log ==

See ERModelAIUsage for the full transcript — the same 2026-04-21 session produced the use-case documentation. The defining student prompt was:

> I'm going solo do everything that you need to do, and tell me after what do I need to do

which led the AI to pick "solo → 3 minimum per rubric → document 7 for a margin" as a default.

> '''Student action required:''' append any future refinements of the use-case list or scenarios here.


=== Session 2 — 2026-08-06 / 2026-08-07 ===

No changes were made to the use-case model in this session: the actor list, the
seven use cases and the scenario SQL in `UseCase0001`–`UseCase0007` are as
produced on 2026-04-21. The SQL in those scenarios was, however, re-verified by
executing the corresponding prototype flows against a live PostgreSQL 16
database, including the failure paths (insufficient funds, insufficient holding,
duplicate registration, wrong password). The results are documented per use case
on the `UseCaseXXXXImplementation` pages.

=== Session 3 — 2026-09-16 ===

Driven by the design review logged in full in the Session 3 — 2026-09-16 section of
ERModelAIUsage:
placing a sell order checked `holdings.quantity` directly, with no way to
record that part of a position was already promised to another, unsettled
order.

'''What changed:'''

 * UseCase0005 — the scenario now reserves the crypto
   (`holdings.reserved_quantity`) before removing it from the position, checks
   `quantity - reserved_quantity` rather than raw `quantity`, and adds a
   worked example and a note on why the reserve and settle steps stay inside
   one transaction rather than two (only market orders are implemented, and
   splitting into two commits would risk an order stuck `open` with no cancel
   use case to recover it).
 * UseCase0004 — no change to the balance logic, but the
   order insert now goes through `status='open'` before a final
   `UPDATE ... SET status='executed'`, matching the sell side, so `Orders`
   genuinely has the lifecycle ERModel
   describes for it rather than a status column that is only ever written
   once.
 * UseCase0006 — the `v_portfolio` reference and its query
   gained `reserved_quantity`/`available_quantity`, since the portfolio screen
   is where a Trader would actually see the new field.
 * The use-case importance table and UC0005's one-line description in
   !UseCaseModel were reworded to mention the reservation.

Every changed scenario's SQL was re-run against the live database, including a
two-concurrent-sells test that reproduces the exact bug being fixed: see
UseCase0005Implementation.

'''What I decided:''' to keep this a revision of the existing UC0004/UC0005
pages rather than a new use case (e.g. "cancel order") — `cancelled` remains
an unused status, same as before, since nothing in the prototype produces it
and inventing a cancel flow was not what the review asked for.