K8: materialization owned by core; one value-to-JSON encoder; result file kinds as a family

[trissim]

K8 · PR #1208 · guards 3/3 · production −341 +300 · tests −155 +266

Receipt: docs/refactor/consolidation-20261009/K8-contract-materialization.md (deletion certificates and the tests-only list are there).

What changed

• Contract half: closure note; it landed with G5.
• openhcs/processing/materialization/ is now openhcs/core/materialization/. Every importer is updated; there is no re-export.
• json_payload_value, JsonPayloadAuthority and benchmark/validation/corpus.py::_json_value are replaced by python_introspect.to_jsonable. ColumnarRows, DataFrame and Series join by registration.
• FileFormat(Enum) is the ResultFileFormat family (core/result_file_formats.py). Each kind owns its suffixes, its preview and how the browser opens it. RESULT_FILE_ACTIONS, ResultFileAction and the inventory's member lists are deleted, along with four unreferenced members.
• The unused SecondaryObjectStats computation in identify_secondary_objects is deleted, with its class.
• Template-crop tests follow the checkpoint naming rule of 0dd77da46; no production change.
• Guards: tests/unit/test_k8_materialization_guards.py. Two FileFormat rows leave E1's enum-dispatch table.

Owner decision (K8-Q1)
User custom functions that import openhcs.processing.materialization fail on import until edited to openhcs.core.materialization. Default: no tool, same as G7-Q1 and K4-Q1.

Checks

• Guards: 3 passed.
• 142 unit files that import the moved or changed modules: 4,279 passed, 10 failed, 2 errors. Nine failures are the same nine on origin/main (44980dfe2). The tenth (test_synthetic_plate_mcp_progress[False]) and the two errors (test_classification_two_vector_authoring) pass when run alone, here and on main.
• tests/pyqt_gui/test_image_browser_filter_controller.py: 8 passed (3 failed on main for a stale stub, fixed here).
• Official30 parity under flock: passed (21:01) at 3c6ace299. Later commits change only the result-file preview reader and the image browser. An earlier run failed because the client reached another worktree's execution server.
• Structural ratchet (openhcs) and nra-r1 exit 1 because of the move: both key counts by file path, so the moved files' unchanged counts show as new under the new path and gone under the old one. No other key increased. scripts and benchmark ratchets exit 0.

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