Extraire les règles métier (legacy)

description: Mine business logic from legacy code into testable, human-readable rule specifications

argument-hint: <system-dir> [module-pattern]

Extract the business rules embedded in legacy/$1 into a structured,

testable specification — the institutional knowledge that's currently locked

in code and in the heads of engineers who are about to retire.

Scope: if a module pattern was given ($2), focus there; otherwise cover the

entire system. Either way, prioritize calculation, validation, eligibility,

and state-transition logic over plumbing.

Method

Spawn three business-rules-extractor subagents in parallel, each assigned

a different lens. If $2 is non-empty, include "focusing on files matching

$2" in each prompt.

1. Calculations — "Find every formula, rate, threshold, and computed value

in legacy/$1. For each: what does it compute, what are the inputs, what is

the exact formula/algorithm, where is it implemented (file:line), and what

edge cases does the code handle?"

1. Validations & eligibility — "Find every business validation, eligibility

check, and guard condition in legacy/$1. For each: what is being checked,

what happens on pass/fail, where is it (file:line)?"

1. State & lifecycle — "Find every status field, state machine, and

lifecycle transition in legacy/$1. For each entity: what states exist,

what triggers transitions, what side-effects fire?"

Synthesize

Merge the three result sets. Deduplicate. For each distinct rule, write a

Rule Card in this exact format:

### RULE-NNN: <plain-English name>
**Category:** Calculation | Validation | Lifecycle | Policy
**Priority:** P0 | P1 | P2
**Source:** `path/to/file.ext:line-line`
**Plain English:** One sentence a business analyst would recognize.
**Specification:**
  Given <precondition>
  When  <trigger>
  Then  <outcome>
  [And  <additional outcome>]
**Parameters:** <constants, rates, thresholds with their current values>
**Edge cases handled:** <list>
**Suspected defect:** <optional — legacy behavior that looks wrong; decide preserve-vs-fix during transform>
**Confidence:** High | Medium | Low — <why; if < High, state the exact SME question>

Priority heuristic — default to P1. Assign P0 if the rule moves money,

enforces a regulatory/compliance requirement, or guards data integrity (and

flag P0 rules at <High confidence as SME-required). Assign P2 for

display/formatting/convenience rules. The downstream /modernize-brief

behavior contract is built from the P0 rules, so assign deliberately.

Write all rule cards to analysis/$1/BUSINESS_RULES.md with:

• A summary table at top (ID, name, category, priority, source, confidence)
• Rule cards grouped by category
• A final "Rules requiring SME confirmation" section listing every

Medium/Low confidence rule with the specific question a human needs to answer

Generate the DTO catalog

As a companion, create analysis/$1/DATA_OBJECTS.md cataloging the core

data transfer objects / records / entities: name, fields with types, which

rules consume/produce them, source location.

Present

Report: total rules found, breakdown by category, count needing SME review.

Suggest: glow -p analysis/$1/BUSINESS_RULES.md