test(metadata): Java conformance harness over shared fixtures/conformance/ corpus

Parametric JUnit 4 runner that auto-discovers fixtures under
fixtures/conformance/, lints each expected-errors.json against the
canonical ERROR-CODES.json registry, and asserts canonical round-trip
(happy path) or error-code-set match (error path). Per-fixture
classification against conformance-expected-failures.json: pass /
known-gap / fixed-but-listed / fail.

Five new files mirroring the C# shape oracle:
- CorpusRoot.java         — repo-root walker (extracted from CanonicalJsonParserTest)
- FixtureDiscovery.java   — fixture enumeration + expectation flags
- FixtureLint.java        — corpus-integrity lint (registered-codes check
                            + script.json shape + ERROR-CODES.json loader)
- ExpectedFailures.java   — ledger load + classify
- ConformanceTest.java    — @RunWith(Parameterized) runner with lint+conformance methods

Java-specific divergences from the C# oracle (each honestly captured in the
ledger when it affects a fixture):
- Provider set: Java uses ServiceLoader auto-registration; providers.json
  is not yet composable in the Java loader. Fixtures requiring an alternate
  provider set are ledgered.
- Loader-root-name leak: the Java loader's MetaRoot name is the loader name.
  The runner pre-scans the first input file's metadata.root.package and
  passes it as the loader name so canonical round-trips produce the right
  top-level "package" key.
- Effective serialization / warnings / scripts: not implemented in the Java
  harness yet — fixtures using expected-effective.json, expected-warnings.json,
  or script.json are ledgered.

Ledger lists the honest current Java gap (72 of 80 fixtures). Stage-1
source-v2 fixtures Unit 1 enabled are passing for Java natively (e.g.
error-reserved-word-as-attr, error-source-no-primary) and are NOT in
the ledger.

Conformance runner: 160 parametric tests (80 lint + 80 conformance),
all green with the populated ledger.
Metadata module: 566/566 tests pass (up from 406, +160 from this harness).
Full reactor: BUILD SUCCESS.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: dmealing

server/java/metadata/conformance-expected-failures.json

@@ -0,0 +1,77 @@
+{
+  "language": "java",
+  "fixtures": [
+    "attr-default-polymorphic",
+    "attr-filter-explicit-ops",
+    "attr-filter-shorthand",
+    "attr-properties-basic",
+    "auto-set-on-create",
+    "auto-set-on-create-and-update",
+    "auto-set-on-update",
+    "currency-default-usd",
+    "currency-explicit-jpy",
+    "currency-precedence-field-vs-view",
+    "enum-abstract-extends",
+    "enum-array",
+    "enum-inline",
+    "error-attr-bad-allowed-value",
+    "error-attr-filter-bad-field",
+    "error-attr-filter-bad-op",
+    "error-attr-filter-legacy-string",
+    "error-attr-missing-required",
+    "error-attr-wrong-type",
+    "error-data-grid-bad-sort-field",
+    "error-extends-nonexistent",
+    "error-field-object-storage-flattened-array",
+    "error-field-object-storage-no-object-ref",
+    "error-origin-bad-aggregate-fn",
+    "error-origin-bad-via-path",
+    "error-parse-malformed-json",
+    "error-source-multiple-primary",
+    "error-template-payload-ref-unresolved",
+    "error-template-prompt-missing-payload-ref",
+    "error-template-required-slot-missing",
+    "error-unknown-relationship-subtype",
+    "extends-abstract-base",
+    "extends-cross-file",
+    "extends-multi-level",
+    "extends-single-level",
+    "field-decimal-precision-scale",
+    "field-object-storage-flattened",
+    "field-object-storage-flattened-nullable",
+    "field-object-storage-jsonb-array",
+    "field-object-storage-jsonb-single",
+    "field-string-maxlength",
+    "identity-primary-and-secondary",
+    "identity-reference-simple",
+    "layout-data-grid-basic",
+    "layout-data-grid-multiple-named",
+    "loader-basic-explicit-subtype",
+    "loader-basic-multi-file-same-package",
+    "loader-basic-single-entity",
+    "loader-filterable-on-indexed-no-warning",
+    "origin-aggregate-count",
+    "origin-aggregate-sum",
+    "origin-collection-simple",
+    "origin-multi-level-via",
+    "origin-passthrough-simple",
+    "overlay-attr-last-writer-wins",
+    "overlay-merge-flag-explicit",
+    "overlay-same-object-different-files",
+    "relationship-one-to-many",
+    "smoke-empty-metadata",
+    "source-db-table-default-schema-omitted",
+    "source-db-table-explicit",
+    "source-db-table-with-schema",
+    "source-db-view-projection",
+    "source-db-view-with-schema",
+    "source-multi-source-roles",
+    "source-rdb-column",
+    "source-rdb-referential-actions",
+    "subtype-entity-missing-primary-warning",
+    "subtype-entity-with-identity",
+    "template-output-and-prompt",
+    "template-prompt-simple",
+    "warning-filterable-no-index"
+  ]
+}