docs(ITC-WP-0016): plan PracticePattern language

Assistant: codex
Assistant-Model: gpt-5.6-sol
Assistant-Session: 01a025c2-407a-7a32-b40a-f37a52f03f62

workplans/ITC-WP-0016-practice-pattern-language.md

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+---
+id: ITC-WP-0016
+type: workplan
+title: "PracticePattern language and InterfaceDeprecationStrangler"
+domain: infotech
+topic_slug: canon
+repo: info-tech-canon
+status: active
+priority: high
+created: "2026-08-21"
+updated: "2026-08-21"
+owner: codex
+related:
+  - STATE-WP-0079
+spec_refs:
+  - infospace/patterns/PracticePatternScheme.md
+  - infospace/patterns/InterfaceDeprecationStrangler.md
+  - infospace/schemas/practice-pattern.schema.yaml
+  - arc-nexus/README.md
+---
+
+# ITC-WP-0016 — PracticePattern language
+
+## Goal
+
+Give recurring operational and architectural practices a stable, speakable
+pattern language in InfoTechCanon. Define a common Markdown scheme inspired by
+Christopher Alexander's pattern-language method, seed it with the proven
+`InterfaceDeprecationStrangler`, and record its adoption in `arc-nexus`.
+
+## T01 — Define the PracticePattern scheme
+
+```task
+id: ITC-WP-0016-T01
+status: progress
+priority: high
+```
+
+Define the identity, lifecycle, required frontmatter, required problem/forces/
+solution structure, evidence expectations, and relationship vocabulary for a
+versioned PracticePattern Markdown artifact. Add a machine-readable schema and
+canon validation for the contract.
+
+## T02 — Document InterfaceDeprecationStrangler
+
+```task
+id: ITC-WP-0016-T02
+status: todo
+priority: high
+```
+
+Capture the reusable practice independently of State Hub: its context, forces,
+solution, staged dynamics, invariants, retirement evidence, failure modes,
+consequences, adoption checklist, and known use in State Hub.
+
+## T03 — Publish retrieval and navigation assets
+
+```task
+id: ITC-WP-0016-T03
+status: todo
+priority: medium
+```
+
+Register the scheme and pattern in the artifact graph, schema catalog, pattern
+index, generated views, and agent retrieval assets. Validate that agents can
+retrieve the named practice without relying on the originating repository.
+
+## T04 — Reference the pattern from arc-nexus
+
+```task
+id: ITC-WP-0016-T04
+status: todo
+priority: medium
+```
+
+State in `arc-nexus` that old architecture interfaces are phased out using the
+canonical `InterfaceDeprecationStrangler` PracticePattern, including the canon
+artifact ID and path and the local adoption expectations.
+
+## Acceptance
+
+- [ ] PracticePattern Markdown artifacts have a documented and validated v0.1 scheme.
+- [ ] `InterfaceDeprecationStrangler` is a registered, retrieval-visible canon artifact.
+- [ ] The pattern distinguishes successful legacy traffic from attempted use of a retired interface.
+- [ ] `arc-nexus` names the pattern and states how it applies locally.
+- [ ] Canon validation and tests pass; both repositories are committed and synchronized.
+
+## Out of scope
+
+- Automatically instrumenting consumer repositories.
+- Rewriting every pre-existing candidate pattern in this workplan.
+- Standardizing protocol-specific deprecation headers beyond requiring explicit caller guidance.