Morgan Lunt 1c4a5cfded
code-modernization: interactive topology map, preflight command, persona flows
modernize-map previously rendered the call graph and data lineage as
static Mermaid diagrams, which become unreadable once a node has ~10+
edges — exactly the shape of real legacy systems. It now builds an
interactive viewer from a shipped template (assets/topology-viewer.html):
a zoomable circle-pack of domains/modules sized by LOC, rendered to
canvas with level-of-detail reveal, dependency edges with per-kind
toggles, search with fly-to, a per-node detail sidebar, and a flow
walkthrough mode. Small domain-level .mmd exports remain for docs.

- topology.json now has a documented schema (hierarchy + edges + entry
  points + observations + flows) consumed by the viewer
- map traces 2-4 business flows anchored to personas (claimant,
  operator, auditor), each step in plain business language mapped to
  the modules that implement it; the viewer plays them as numbered
  paths
- brief gains a Business Walkthroughs section connecting each persona
  flow to the phase that replaces it
- new modernize-preflight command: detects the stack, checks analysis
  tooling, smoke-compiles a real source file with the legacy toolchain,
  inventories missing copybooks/descriptors/binary-only artifacts, and
  writes a per-command readiness verdict
- transform now verifies legacy + target toolchains before its plan
  gate instead of failing at test time
- README: commands updated, optional-tooling section reframed as 'what
  to give Claude'
2026-06-09 08:48:04 -07:00

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---
description: Transform one legacy module to the target stack — idiomatic rewrite with behavior-equivalence tests
argument-hint: <system-dir> <module> <target-stack>
---
Transform `legacy/$1` module **`$2`** into **$3**, with proof of behavioral
equivalence.
This is a surgical, single-module transformation — one vertical slice of the
strangler fig. Output goes to `modernized/$1/$2/`.
## Step 0a — Toolchain check (fail fast)
Verify the build environment **before** planning, not when the tests
first run:
- **Target stack ($3):** runtime, package manager, and test framework all
respond (`java -version` + `mvn -v`, `node -v` + `npm -v`,
`python3 -V` + `pytest --version`, …).
- **Legacy stack (if equivalence tests will execute legacy code):** the
compiler/interpreter works on this codebase — run a syntax-only compile
of the module being transformed (e.g. `cobc -fsyntax-only`).
If anything is missing or the smoke compile fails, stop and report what
to install or fix — suggest `/modernize-preflight $1 $3` for the full
readiness report. Don't enter plan mode on a machine that can't run the
proof.
## Step 0b — Plan (HITL gate)
Read the source module and any business rules in `analysis/$1/BUSINESS_RULES.md`
that reference it. Then **enter plan mode** and present:
- Which source files are in scope
- The target module structure (packages/classes/files you'll create)
- Which business rules / behaviors this module implements
- How you'll prove equivalence (test strategy)
- Anything ambiguous that needs a human decision NOW
Wait for approval before writing any code.
## Step 1 — Characterization tests FIRST
Before writing target code, spawn the **test-engineer** subagent:
"Write characterization tests for legacy/$1 module $2. Read the source,
identify every observable behavior, and encode each as a test case with
concrete input → expected output pairs derived from the legacy logic.
Target framework: <appropriate for $3>. Write to
`modernized/$1/$2/src/test/`. These tests define 'done' — the new code
must pass all of them."
Show the user the test file. Get a 👍 before proceeding.
## Step 2 — Idiomatic transformation
Write the target implementation in `modernized/$1/$2/src/main/`.
**Critical:** Write code a senior $3 engineer would write from the
*specification*, not from the legacy structure. Do NOT mirror COBOL paragraphs
as methods, do NOT preserve legacy variable names like `WS-TEMP-AMT-X`.
Use the target language's idioms: records/dataclasses, streams, dependency
injection, proper error types, etc.
Include: domain model, service logic, API surface (REST controller or
equivalent), and configuration. Add concise Javadoc/docstrings linking each
class back to the rule IDs it implements.
## Step 3 — Prove it
Run the characterization tests:
```bash
cd modernized/$1/$2 && <appropriate test command for $3>
```
Show the output. If anything fails, fix and re-run until green.
## Step 4 — Side-by-side review
Generate `modernized/$1/$2/TRANSFORMATION_NOTES.md`:
- Mapping table: legacy file:lines → target file:lines, per behavior
- Deliberate deviations from legacy behavior (with rationale)
- What was NOT migrated (dead code, unreachable branches) and why
- Follow-ups for the next module that depends on this one
Then show a visual diff of one representative behavior, legacy vs modern:
```bash
delta --side-by-side <(sed -n '<lines>p' legacy/$1/<file>) modernized/$1/$2/src/main/<file>
```
## Step 5 — Architecture review
Spawn the **architecture-critic** subagent to review the transformed code
against $3 best practices. Apply any HIGH-severity feedback; list the rest
in TRANSFORMATION_NOTES.md.
Report: tests passing, lines of legacy retired, location of artifacts.