docs(WO88): the secryst migration program

TODO.sota/88-secryst-migration.md

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+# WO88 — full migration of the secryst-lineage models into the framework
+
+Status: IN_PROGRESS (2026-10-24, owner-directed: "fully migrate them
+to interscript in our new framework")
+
+The secryst-era models (khm-latn-1.0, the legacy tha-g2p line) predate
+the contract: no recipes, no corpora pins, no documented targets
+(WO87's audit), thin provenance. Migration = bring each into the
+2-YAML + gates world so every future retrain/release runs the same
+lawful path.
+
+## Step 1 — metadata migration (this WO, now)
+- `corpora/khm-latn.yaml`: the secryst lineage documented with honest
+  UNVERIFIED markers where provenance is not yet pinned (the training
+  corpus predates pinning; the decode evidence + khmer-dict-spice
+  source are documented).
+- `recipes/khm-latn.yaml`: the retrain contract for the
+  framework-native khm-latn (the WO68/82 path).
+
+## Step 2 — retrain under gates (the real migration)
+Each legacy line retrains through recipes+gates; the legacy artifact
+stays resolvable via index aliases until its successor passes.
+Order: khm-latn (B7 owner data pending → blocked), tha-phonemic
+legacy line (superseded by tha-phonemic-1.0 — retire, don't retrain),
+urd/fas lines (gates already apply to their successors).
+
+## Acceptance
+Every id in models.yaml carries recipe+corpus or an explicit
+retire note; nothing remains outside the contract.