docs(phase-19.6): add research and validation strategy

.planning/phases/19.6-two-factor-auth-and-device-flow-in-sm-user-plugin/19.6-VALIDATION.md

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+---
+phase: "19.6"
+slug: "two-factor-auth-and-device-flow-in-sm-user-plugin"
+# status lifecycle: draft (seeded by plan-phase) → validated (set by validate-phase §6)
+# audit-milestone §5.5 distinguishes NOT-VALIDATED (draft) from PARTIAL (validated + nyquist_compliant: false) (#2117)
+status: draft
+nyquist_compliant: false
+wave_0_complete: false
+created: "2026-10-21"
+---
+
+# Phase 19.6 — Validation Strategy
+
+> Per-phase validation contract for feedback sampling during execution.
+
+---
+
+## Test Infrastructure
+
+| Property | Value |
+|----------|-------|
+| **Framework** | Go `testing` + `httptest`; testcontainers-go Postgres (DB tests skip under `-short`) |
+| **Config file** | none — Wave 0 adds `sm-mfa-plugin/testmain_test.go` and `harness_test.go` (copied from `sm-sociallogin-plugin`) |
+| **Quick run command** | `go -C ../sm-mfa-plugin test -short ./...` and `go -C ../fonoteka.go test -short ./plugins/golem15/user/...` |
+| **Full suite command** | `scripts/check-phase19.6.sh` (go, userplugin, mfa, sociallogin, demo, bm, fonoteka, docker, docs stages) |
+| **Estimated runtime** | ~180 seconds (full, with Docker) |
+
+---
+
+## Sampling Rate
+
+- **After every task commit:** `go vet ./...` + `go test -short ./...` of the touched repo
+- **After every plan wave:** full suites (Docker) of every touched repo
+- **Before `/msd-verify-work`:** `scripts/check-phase19.6.sh` must be green
+- **Max feedback latency:** 60 seconds for the short loop
+
+---
+
+## Per-Task Verification Map
+
+Decision → test map is in `19.6-RESEARCH.md` § Validation Architecture; the planner assigns task IDs.
+
+| Task ID | Plan | Wave | Requirement | Threat Ref | Secure Behavior | Test Type | Automated Command | File Exists | Status |
+|---------|------|------|-------------|------------|-----------------|-----------|-------------------|-------------|--------|
+| 19.6-XX-XX | TBD | TBD | D-XX | T-19.6-XX | per RESEARCH map | unit/integration | per RESEARCH map | ❌ W0 | ⬜ pending |
+
+*Status: ⬜ pending · ✅ green · ❌ red · ⚠️ flaky*
+
+---
+
+## Wave 0 Requirements
+
+- [ ] `sm-mfa-plugin/testmain_test.go`, `harness_test.go` — boot `golem15.user` + `golem15.mfa`
+- [ ] WebAuthn fixtures — recorded attestation/assertion JSON or a virtual authenticator
+- [ ] Clock injection for TOTP tests
+- [ ] user-plugin harness helper for device-flow tests
+
+---
+
+## Manual-Only Verifications
+
+| Behavior | Requirement | Why Manual | Test Instructions |
+|----------|-------------|------------|-------------------|
+| WebAuthn registration and login in a real browser | D-08 / SC-1 | Browser authenticator ceremony cannot run in `go test` | Register a passkey on the demo instance over HTTPS with a hostname RP ID, then sign in with it |
+
+---
+
+## Validation Sign-Off
+
+- [ ] All tasks have `<automated>` verify or Wave 0 dependencies
+- [ ] Sampling continuity: no 3 consecutive tasks without automated verify
+- [ ] Wave 0 covers all MISSING references
+- [ ] No watch-mode flags
+- [ ] Feedback latency < 60s
+- [ ] `nyquist_compliant: true` set in frontmatter
+
+**Approval:** pending