M1: Eliminate .unwrap()/.expect() from src/pricing/ (#318)

[joaquinbejar]

Closes #318.

Summary

Remove every production .unwrap() / .expect() from src/pricing/ (M1 — Panic-Free Core, 0.16.0). Total: 48 sites across 10 files → 0.

Acceptance grep is clean:

for f in $(find src/pricing -name '*.rs'); do
  awk '/#\[cfg\(test\)\]/{exit} {print}' "$f" | grep -nE '\.unwrap\(\)|\.expect\('
done
# (no output)

Approach

Per-file site counts:

File	Sites	Pattern
utils.rs	11	sqrt + from_f64 + Normal::new + chain unwraps → ? via PricingError::method_error / DecimalError
telegraph.rs	9	mostly ?; F-blocker next_state -> i8 resolved in-place with unwrap_or(0.0) + tracing::warn!
payoff.rs	6	4 doctests rewrapped in # fn run() -> Result<...>; F-blocker standard_payoff -> f64 resolved in-place
american.rs	5	doctests rewrapped
barrier.rs	4	from_f64 + sqrt → ok_or_else + ?
asian.rs	4	sqrt + Positive::new → map_err / ?
monte_carlo.rs	3	to_f64 + from_usize → ok_or_else + ?
cliquet.rs	3	partial_cmp guarded with NaN check, 2 from_f64 → ?
binomial_model.rs	2	Vec::collect::<Result<_, _>>()? + 1 doctest wrap
compound.rs	1	Positive::new(2.0) → map_err + ?

Both F-blockers (telegraph::next_state -> i8 and payoff::standard_payoff -> f64) used the in-place unwrap_or(safe_default) + tracing::warn! strategy because:

1. next_state: probability is provably bounded [0, 1] (just compared < probability after sampling random::<f64>()).
2. standard_payoff: (spot - strike).max(Decimal::ZERO) is the max of two finite Decimals, provably finite.

Both fall under rules/global_rules.md §Numerical Discipline (NaN/Inf guard at f64↔Decimal boundaries), matching the precedent in PR #348 for chains/utils.rs::adjust_volatility.

panic! / unreachable! / unimplemented! / assert! are intentionally left in place — they belong to issue #292.

Public API impact

None. All pub fn signatures preserved. Trait surfaces (Payoff, PayoffInfo, Profit) unchanged. No new error variants. No new From impls. README regen produces no diff.

One test repair: #[should_panic] test test_probability_keep_under_strike_zero_volatility (utils.rs:647) became assert!(... .is_err()) since the panic is now a typed DecimalError — exactly the goal of this issue.

Verification

• cargo build --all-targets --all-features — clean.
• cargo clippy --all-targets --all-features --workspace -- -D warnings — clean.
• cargo fmt --all --check — clean.
• cargo test --lib pricing:: — 240 passed; 0 failed.
• cargo test --lib --no-fail-fast — 3723 passed; 0 failed; 5 ignored.
• cargo test --doc — 203 passed; 0 failed.
• cargo build --release — clean.

Commit map

1. refactor(pricing): panic-free src/pricing/* (48 sites, no API change)

Test plan

• cargo build --all-targets --all-features clean
• cargo clippy --all-targets --all-features --workspace -- -D warnings clean
• cargo fmt --all --check clean
• cargo test --lib clean
• cargo test --doc clean
• cargo build --release clean
• Reviewer confirms in-place unwrap_or + tracing::warn! strategy is acceptable for the two F-blockers (telegraph::next_state, payoff::standard_payoff)

[codecov]

Codecov Report

❌ Patch coverage is 61.31387% with 53 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/pricing/telegraph.rs	48.57%	18 Missing ⚠️
src/pricing/monte_carlo.rs	38.88%	11 Missing ⚠️
src/pricing/barrier.rs	53.33%	7 Missing ⚠️
src/pricing/utils.rs	80.00%	7 Missing ⚠️
src/pricing/cliquet.rs	44.44%	5 Missing ⚠️
src/pricing/payoff.rs	60.00%	4 Missing ⚠️
src/pricing/asian.rs	90.90%	1 Missing ⚠️

Files with missing lines	Coverage Δ
src/pricing/american.rs	90.32% <ø> (ø)
src/pricing/binomial_model.rs	83.51% <100.00%> (ø)
src/pricing/compound.rs	77.16% <100.00%> (+0.21%)	⬆️
src/pricing/asian.rs	81.48% <90.90%> (-0.08%)	⬇️
src/pricing/payoff.rs	63.33% <60.00%> (-4.85%)	⬇️
src/pricing/cliquet.rs	82.43% <44.44%> (-5.81%)	⬇️
src/pricing/barrier.rs	72.35% <53.33%> (-3.96%)	⬇️
src/pricing/utils.rs	88.42% <80.00%> (-6.32%)	⬇️
src/pricing/monte_carlo.rs	73.17% <38.88%> (-26.83%)	⬇️
src/pricing/telegraph.rs	80.50% <48.57%> (-11.97%)	⬇️

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[Copilot]

Pull request overview

This PR advances the project’s “panic-free core” milestone by removing .unwrap() / .expect() usage from production code under src/pricing/, converting previously panicking numeric conversions and Option-returning math ops into typed error paths (and updating doctests accordingly).

Changes:

• Replaced unwrap()/expect() in pricing computations (e.g., Decimal::sqrt, Decimal::{from_f64,to_f64}, distribution construction) with ?, ok_or_else, and typed PricingError/DecimalError propagation.
• Updated doctests/examples to compile under fallible APIs by wrapping examples in # fn run() -> Result<...> blocks and using ?.
• For the two “f-blocker” sites that cannot easily change signatures, introduced unwrap_or(safe_default) behavior with tracing::warn! to avoid panics.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
src/pricing/utils.rs	Replaces sqrt / from_f64 / Normal::new unwraps with typed DecimalError paths; updates a panic-based test to assert an error instead.
src/pricing/telegraph.rs	Removes unwraps in state transition and simulation loop; adds warning+default on a conversion failure path.
src/pricing/payoff.rs	Removes to_f64().unwrap() in standard_payoff via unwrap_or_else + warn!; updates doctest snippets.
src/pricing/monte_carlo.rs	Converts payoff/rate conversions to error-returning paths instead of panicking; fixes Decimal::from_usize unwrap.
src/pricing/compound.rs	Replaces Positive::new(...).unwrap() with map_err + ?.
src/pricing/cliquet.rs	Guards partial_cmp sorting by explicitly rejecting NaN reset dates; replaces from_f64 unwraps with errors.
src/pricing/binomial_model.rs	Eliminates unwrap in initial payoff vector creation via collect::<Result<_,_>>()?; updates doctest.
src/pricing/barrier.rs	Converts from_f64 and sqrt unwraps into typed PricingError paths.
src/pricing/asian.rs	Removes Positive::new(...).unwrap() and replaces sqrt(t) unwrap usage with a typed error.
src/pricing/american.rs	Updates module/function doctests to use fallible Positive::new(...)? instead of unwrap.

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[joaquinbejar]

Thanks for the review. Seven of the eight comments are addressed in c162f41 (5 docstring fixes plus the sqrt error wording and the telegraph zero-guard). The remaining lambda_dt branch bug is a real pre-existing logic error and is tracked separately in #351.