feat(wren-mdl): loosen manifest schema and bump layout version to 4

[goldmedal]

What

A new MDL layout revision (v4): additive, backward-compatible annotation fields on the manifest schema, plus the matching supported-layout-version bump.

Schema (core/wren-mdl/mdl.schema.json)

1. Widen column.properties value types to string | number | boolean | object | array | null, matching model / relationship / view (column was string-only — an inconsistency).
2. Add optional manifest-level description + properties.
3. Add model.uniqueKeys (a column or list of columns, like primaryKey).
4. Add optional description + properties to cube measure / cubeDimension / timeDimension.

Layout version (core/wren-core-base)

• Bump MAX_SUPPORTED_LAYOUT_VERSION 3 → 4 and add the no-op migrate_v3_to_v4 step — matching the precedent of v2 (optional dialect) and v3 (composite primaryKey), both additive no-op migrations.

Why

Give natively-typed homes for human/agent descriptions, business context, and uniqueness metadata — useful for knowledge annotations and semantic-layer interop — instead of forcing everything through opaque string bags.

Compatibility

All changes are additive or validation-widenings; existing manifests stay valid and v3→v4 is a no-op. No query-engine / semantic-logic changes: the manifest structs don't set #[serde(deny_unknown_fields)], so unknown fields were already ignored — the only Rust delta is the version const + the no-op migration + tests. wren-core-base: 46 tests + clippy + fmt clean locally.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features
  • Added support for descriptions on measures, cube dimensions, and time dimensions.
  • Added model-level description plus flexible model properties and expanded custom property value types.
  • Added uniqueKeys support for both single-column and composite uniqueness definitions.
• Compatibility / Maintenance
  • Extended manifest layout version support to version 4 and added migration handling for 3 → 4.
  • Updated tests to verify the 3 → 4 layout version migration behavior.

[coderabbitai]

Walkthrough

The MDL schema now supports richer custom-property values, adds descriptions and root metadata, defines single-column or composite model unique keys, and introduces layout version 4 validation with a no-op migration from version 3.

Changes

MDL schema and versioning

Layer / File(s)	Summary
Metadata fields and flexible properties core/wren-mdl/mdl.schema.json	Column, measure, cube dimension, time dimension, and root manifest properties accept multiple JSON value types; descriptions, root metadata, and single-column or composite model unique keys are added.
Layout version 4 validation and migration core/wren-core-base/src/mdl/manifest.rs, core/wren-core-base/src/mdl/migration.rs	Manifest validation accepts layout version 4, and migration from version 3 to 4 updates the version without transforming manifest content; a unit test covers the transition.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• Canner/WrenAI#1934: Broadens properties.additionalProperties types in the same MDL schema.
• Canner/WrenAI#2281: Updates related cube schema definitions.

Suggested reviewers: wwwy3y3, douenergy

Poem

I’m a rabbit with schema keys,
Hopping through richer metadata trees.
Version four joins the burrow bright,
Old manifests change their tag just right.
With flexible fields and unique keys,
MDL grows among the trees.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly reflects the main changes: schema loosening and a layout version bump to 4.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/mdl-schema-loosen-properties

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[coderabbitai]

🧹 Nitpick comments (1)

core/wren-core-base/src/mdl/migration.rs (1)

145-151: 🗄️ Data Integrity & Integration | 🔵 Trivial | ⚡ Quick win

Exercise representative v4 fields in the migration test.

The test currently verifies only layoutVersion; include descriptions, nested properties, and composite uniqueKeys to ensure the no-op migration preserves the new metadata and richer JSON values.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@core/wren-core-base/src/mdl/migration.rs` around lines 145 - 151, Expand
test_migrate_v3_to_v4 with representative v4 input fields, including a
description, nested properties, and composite uniqueKeys. After
migrate_manifest, assert these metadata and nested JSON values remain unchanged
alongside the existing layoutVersion assertion, verifying the no-op migration
preserves richer v4 content.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@core/wren-core-base/src/mdl/migration.rs`:
- Around line 145-151: Expand test_migrate_v3_to_v4 with representative v4 input
fields, including a description, nested properties, and composite uniqueKeys.
After migrate_manifest, assert these metadata and nested JSON values remain
unchanged alongside the existing layoutVersion assertion, verifying the no-op
migration preserves richer v4 content.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: d9e5685d-017f-4666-bd3d-356720127414

📥 Commits

Reviewing files that changed from the base of the PR and between b215a87 and 0cc7608.

📒 Files selected for processing (2)

• core/wren-core-base/src/mdl/manifest.rs
• core/wren-core-base/src/mdl/migration.rs