Legacy Modernization Pattern — Workflow

Pattern: Legacy Modernization
Component: workflow.md
Version: 1.1 | Updated: 2026-07-16

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End-to-end flow

Step procedure

Step	Actor	Action	Exit criteria
1	Human	Select capability slice	Bounded backlog item
2	Behavior Mapper	Document golden behaviors + edge cases	Characterization notes
3	Modernization Lead	Choose seam (facade, proxy, event, data)	Seam ADR
4	Coder	Implement new path behind flag	Feature-flagged
5	Parity Harness	Compare legacy vs new on fixtures + shadow	Gate green
6	Traffic Shift	Ramp % with abort KPIs	100% or abort
7	Human + eng	Retire legacy path for slice	Retirement checklist done
8	Program	Pick next slice	Repeat

Deviation rule

If parity fails in production shadow, do not increase traffic. Fix or narrow the slice. Never skip to 100% to “make the demo.”

Parallelism rule

Independent capability slices may proceed in parallel only if seams do not contend on the same legacy write path without a coordination plan.