refactor: consolidate the production workflow runtime

docs/ARCHITECTURE.md

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+# Architecture
+
+Book Translator has one supported workflow runtime.
+
+The current workflow is repository-authoritative and uses one durable state contract: schema-versioned metadata/progress, explicit source identity and corpus manifest, durable claims, machine review evidence, coordination, finalize/build state, and backend-neutral compare-and-swap storage.
+
+## Supported runtime
+
+- `scripts/book.py` is the primary CLI entrypoint.
+- `scripts/corpus.py` owns source-corpus integrity and restore operations.
+- `scripts/workflow_v2/` is the internal workflow package. The `v2` suffix is an implementation-era module name, not a second supported workflow version.
+- `docs/ORCHESTRATION.md` and `docs/TRANSLATION.md` are the canonical execution contracts.
+- Files under `books/<slug>/` are authoritative durable book state.
+
+## State contract
+
+Every supported book workspace uses the current schema and must contain current workflow provenance, explicit source identity, a sealed source manifest, and machine review evidence. Missing schema versions, legacy lifecycle-only review state, unsealed legacy source state, and workflow migration journals are not supported runtime modes.
+
+An older workspace must be converted outside the production runtime before it is used. The current runtime does not auto-normalize legacy schemas and does not perform workflow-version migrations.
+
+## Runtime boundaries
+
+The orchestration core owns state transitions. Translator and Reviewer roles produce artifacts and decisions but do not race shared mutable state. Storage backends provide create-if-absent and compare-and-swap semantics; filesystem and GitHub API storage implement the same contract.
+
+Source integrity is independent from literary review. A valid source corpus does not imply a reviewed translation, and a Reviewer PASS does not replace structural or source-integrity validation.
+
+## Completion
+
+A book is complete only when all intended units have current machine-verifiable PASS evidence, durable lifecycle state is reviewed, structural and corpus checks pass, and requested output artifacts are built and verified.