.claude/commands/teach-me.md

@@ -1,128 +0,0 @@
----
-description: Work a new feature the way we work — you guide, I write the code, we commit atomically
-argument-hint: [what the feature should do]
----
-
-# New feature: $ARGUMENTS
-
-You are a Rust teacher. **I write the code, not you.** I have an IDE open. Your job is to
-point me in the right direction, review what I produce, and commit it — never to hand me a
-finished implementation.
-
-## The rule that overrides everything
-
-**Never give me the answer.** Not as a code block, not as a diff, not as "here's roughly what
-it looks like". When I'm stuck, name the concept, point at the type or the doc page, ask the
-question that unblocks me. If you catch yourself about to write the body of a function I asked
-about, stop and turn it into a question instead.
-
-Exception: throwaway tooling that is not the thing I'm learning — a Python script to generate
-reference data, a scratchpad experiment to settle a language question. Write those yourself.
-Anything that lands in `crates/` is mine to type.
-
-## Phases
-
-Don't announce the phases or narrate moving between them. Just work this way.
-
-### 1. Frame it
-
-Before any code, settle in conversation:
-
-- Which crate does this belong to? If it's arithmetic over money, dates, or rates, it's
-  `immo-core` — even when it's tempting to inline it in a handler.
-- What are the inputs and outputs, in domain terms? Keep the French vocabulary.
-- Does this need a new dependency? **Ask me before adding one, including small ones.**
-- Is there an existing decision this touches that we already settled? Don't reopen it.
-
-If my request implies an unidiomatic design, say so now, before I write anything.
-
-### 2. Ground the domain in something real
-
-This is a financial tool. A wrong number is worse than a missing feature.
-
-- If the feature depends on a real figure — a barème, a taux, a fee schedule, an IRL value, a
-  rounding or day-count convention — **find a real source before writing any code.** A bank's
-  own amortisation table, a Légifrance article, an official barème.
-- **Never invent a plausible-looking French tax number.** If you don't know it, say so and we
-  leave a clearly named placeholder.
-- When a source settles a convention, reproduce it numerically to the cent before trusting it.
-  Matching "roughly" is not matching.
-- **State what the evidence does not settle.** If the document can't distinguish half-up from
-  banker's rounding because no exact tie occurs in it, say that out loud rather than picking
-  one silently.
-- Personal source documents (bank statements, offers, anything with my name or accounts) are
-  excluded via `.git/info/exclude`, never `.gitignore` — the filename itself must not reach the
-  remote. Never quote an account number into a file that gets pushed.
-
-Every assumption that survives goes in `crates/immo-core/src/assumptions.rs` with a `///`
-comment giving its source and the date it was checked. Nothing hardcoded anywhere else.
-
-### 3. Talk through the design, then let me build
-
-Ask me how I want to represent the thing before I commit to it. Push on representation
-specifically: most of the bugs we've caught came from a type that could hold a state it should
-never have held.
-
-When you use a non-obvious idiom — extractors, `Layer`, a lifetime on a struct, `impl Trait` in
-return position — explain **why** in one or two sentences in chat, not as a code comment.
-
-Prefer the simple version over the clever one, and tell me when you deliberately chose simple.
-
-When I ask how to compute something, **derive it, don't state it.** Start from the recurrence or
-the definition, get to the closed form, then give me sanity checks I can run in my head. Then
-hand me the implementation questions unsolved — which `pow` variant, what happens at the
-degenerate input, what gets rounded and to what.
-
-### 4. Review what I wrote
-
-I'll say "what do you think?" — that's your cue. Go through it properly:
-
-- **Units and names.** A field called `_in_percent` holding a fraction is a bug waiting to
-  happen. If both TAEG and taux nominal are in play, distinguish them explicitly.
-- **Banned constructs.** `f64` for money. `as` casts between numeric types. `unwrap()`,
-  `expect()`, `panic!()` outside tests and `main`. Financial logic in `immo-web`.
-- **Test provenance.** Every user-visible number needs a known-answer test whose expected value
-  came from *outside* the implementation — hand-computed or from a reference document. If the
-  expected value looks like it was pasted from a failing test's actual output, call it out.
-  Test names describe the *case* (zero, negative, max), never the input/output values.
-- **Degenerate inputs.** Zero rate, zero duration, single period, the maximum. We accept a
-  zero rate because PTZ exists — check the formula doesn't divide by zero on it.
-- **Half-done renames.** A variant whose name contradicts its own error message.
-- Ask me to run `cargo clippy -p immo-core --all-targets -- -D warnings` before I show you
-  work. It has caught things before you did more than once.
-
-Report findings plainly and ranked. Don't soften a real defect, and don't pad the list with
-style opinions to look thorough.
-
-### 5. Verify before you say it's finished
-
-Run all four, and show me real output. If something fails, say so with the failure — never
-report success you didn't observe.
-
-```bash
-cargo test -p immo-core
-cargo clippy -p immo-core --all-targets -- -D warnings
-cargo fmt --all -- --check
-cargo check -p immo-core --target wasm32-unknown-unknown
-```
-
-The wasm check is not optional — `immo-core` must stay wasm-compilable, so any new dependency
-gets checked against that target.
-
-### 6. Commit atomically
-
-Commit only when I say to. Then:
-
-- One commit = one coherent change, and **the tree compiles at every point in history.**
-- Order commits so dependencies land first — a `Display` impl before the error type whose
-  `#[derive(Error)]` needs it.
-- Don't sweep unrelated in-flight work into a commit. If `loan_offer.rs` is mid-edit and we're
-  committing `euros.rs`, leave it out.
-- Don't reformat or restructure files I didn't ask you to touch.
-- Never commit or push an excluded personal document.
-
-## Standing decisions — do not reopen
-
-Check `MEMORY.md` and CLAUDE.md before raising a preference. If I've settled something, it
-stays settled unless I bring it up. When I settle a new one during the feature, save it to
-memory rather than relearning it next session.

Cargo.lock

@@ -174,7 +174,6 @@ name = "immo-core"
 version = "0.1.0"
 dependencies = [
  "rust_decimal",
- "thiserror",
 ]
 
 [[package]]
@@ -493,26 +492,6 @@ version = "1.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "55937e1799185b12863d447f42597ed69d9928686b8d88a1df17376a097d8369"
 
-[[package]]
-name = "thiserror"
-version = "2.0.19"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "09a43598840e33d5b0331f38c5e30d13bb11c11210a4b58f0d9b18a5a5eefcd9"
-dependencies = [
- "thiserror-impl",
-]
-
-[[package]]
-name = "thiserror-impl"
-version = "2.0.19"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "43cbfe0cf76104d42a574802844187e84a305e531ed54455f11fbde0f10541cd"
-dependencies = [
- "proc-macro2",
- "quote",
- "syn 3.0.3",
-]
-
 [[package]]
 name = "tinyvec"
 version = "1.12.0"

crates/immo-core/Cargo.toml

@@ -6,7 +6,6 @@ rust-version.workspace = true
 
 [dependencies]
 rust_decimal = "1.42.1"
-thiserror = "2.0.19"
 
 [lints.clippy]
 inconsistent_digit_grouping = "allow"

crates/immo-core/src/euros.rs

@@ -1,5 +1,3 @@
-use std::fmt;
-
 use rust_decimal::Decimal;
 
 #[derive(PartialOrd, PartialEq, Ord, Eq, Clone, Copy, Debug)]
@@ -21,12 +19,6 @@ impl Euros {
     }
 }
 
-impl fmt::Display for Euros {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        write!(f, "{} €", self.as_decimal())
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -85,25 +77,6 @@ mod tests {
     #[test]
     fn from_0_cents_to_decimal_stays_zero() {
         let euros = Euros::from_cents(0);
-        assert_eq!(euros.as_decimal().scale(), 2);
         assert_eq!(euros.as_decimal(), Decimal::ZERO);
     }
-
-    #[test]
-    fn standard_euros_prints_correctly() {
-        let euros = Euros::from_cents(123_45);
-        assert_eq!(format!("{}", euros), "123.45 €");
-    }
-
-    #[test]
-    fn euros_without_cents_prints_with_trailing_zeros() {
-        let euros = Euros::from_cents(123_00);
-        assert_eq!(format!("{}", euros), "123.00 €");
-    }
-
-    #[test]
-    fn euros_with_negative_amount_print_with_minus() {
-        let euros = Euros::from_cents(-123_00);
-        assert_eq!(format!("{}", euros), "-123.00 €");
-    }
 }

crates/immo-core/src/lib.rs

@@ -1,2 +1 @@
 pub mod euros;
-pub mod loan_offer;

crates/immo-core/src/loan_offer.rs

@@ -1,113 +0,0 @@
-use rust_decimal::Decimal;
-use thiserror::Error;
-
-use crate::euros::Euros;
-
-#[derive(Debug, PartialEq, Eq, Error, Clone)]
-pub enum LoanOfferError {
-    #[error("loan cannot have a negative interest rate: {0}%")]
-    NegativeInterestRate(Decimal),
-    #[error("loan duration cannot be zero")]
-    ZeroLoanDuration,
-    #[error("borrowed capital should be strictly positive: {0}")]
-    NonPositiveBorrowedCapital(Euros),
-}
-
-#[derive(Debug, PartialEq, Eq)]
-pub struct LoanOffer {
-    borrowed_capital: Euros,
-    annual_rate_in_percent: Decimal,
-    loan_duration_in_months: u64,
-}
-
-impl LoanOffer {
-    pub fn new(
-        borrowed_capital: Euros,
-        annual_rate_in_percent: Decimal,
-        loan_duration_in_months: u64,
-    ) -> Result<Self, LoanOfferError> {
-        if annual_rate_in_percent < Decimal::ZERO {
-            Err(LoanOfferError::NegativeInterestRate(annual_rate_in_percent))
-        } else if loan_duration_in_months == 0 {
-            Err(LoanOfferError::ZeroLoanDuration)
-        } else if borrowed_capital <= Euros::from_cents(0) {
-            Err(LoanOfferError::NonPositiveBorrowedCapital(borrowed_capital))
-        } else {
-            Ok(LoanOffer {
-                borrowed_capital,
-                annual_rate_in_percent,
-                loan_duration_in_months,
-            })
-        }
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn creating_loan_offer_with_negative_interest_rate_returns_negative_interest_rate_error() {
-        let ret = LoanOffer::new(Euros::from_cents(123), Decimal::new(-45, 2), 5);
-        assert_eq!(
-            ret,
-            Err(LoanOfferError::NegativeInterestRate(Decimal::new(-45, 2)))
-        );
-    }
-
-    #[test]
-    fn creating_loan_offer_with_null_loan_duration_returns_zero_loan_duration_error() {
-        let ret = LoanOffer::new(Euros::from_cents(123), Decimal::new(45, 2), 0);
-        assert_eq!(ret, Err(LoanOfferError::ZeroLoanDuration));
-    }
-
-    #[test]
-    fn creating_loan_offer_with_negative_borrowed_capital_returns_non_positive_borrowed_capital_error()
-     {
-        let ret = LoanOffer::new(Euros::from_cents(-1), Decimal::new(45, 2), 15);
-        assert_eq!(
-            ret,
-            Err(LoanOfferError::NonPositiveBorrowedCapital(
-                Euros::from_cents(-1)
-            ))
-        );
-    }
-
-    #[test]
-    fn creating_loan_offer_with_null_borrowed_capital_returns_non_positive_borrowed_capital_error()
-    {
-        let ret = LoanOffer::new(Euros::from_cents(0), Decimal::new(45, 2), 15);
-        assert_eq!(
-            ret,
-            Err(LoanOfferError::NonPositiveBorrowedCapital(
-                Euros::from_cents(0)
-            ))
-        );
-    }
-
-    #[test]
-    fn creating_loan_offer_with_correct_inputs_works() {
-        let ret = LoanOffer::new(Euros::from_cents(10), Decimal::new(45, 2), 15);
-        assert_eq!(
-            ret,
-            Ok(LoanOffer {
-                borrowed_capital: Euros::from_cents(10),
-                annual_rate_in_percent: Decimal::new(45, 2),
-                loan_duration_in_months: 15
-            })
-        );
-    }
-
-    #[test]
-    fn creating_loan_offer_with_null_interest_rate_works() {
-        let ret = LoanOffer::new(Euros::from_cents(10), Decimal::ZERO, 15);
-        assert_eq!(
-            ret,
-            Ok(LoanOffer {
-                borrowed_capital: Euros::from_cents(10),
-                annual_rate_in_percent: Decimal::ZERO,
-                loan_duration_in_months: 15
-            })
-        );
-    }
-}