Phase 2.2: JSONB inline editing

[aesslinger]

Part of the Phase 2 set of PostgreSQL-specific features beyond the built-in driver.

Problem

JSONB columns are currently edited as a raw text string. For complex nested objects this is error-prone — a single misplaced brace or quote produces an opaque parse failure, and there's no way to modify one nested key without retyping the entire value.

Proposed approach

This is primarily a frontend feature (UI extension); the plugin's role is narrow:

1. Detect JSONB columns and flag them in the get_columns response — already done (data_type: "jsonb").
2. Validate JSON on update_record — return a clear error (with position) if invalid JSON is submitted, instead of a bare Postgres parse error.
3. Optionally expose jsonb_set/jsonb_insert/jsonb_delete_path-style helper operations so the frontend can apply targeted edits.

Plugin-side additions

• New RPC method: validate_jsonb(value) → returns ok, or a parse error with position.
• New RPC method: jsonb_patch(params, table, pk, path, operation, value) → applies a targeted JSONB modification without overwriting the entire value.

Frontend integration

• JSON tree editor component (expand/collapse nodes, edit values inline).
• Add/remove key buttons.
• Path breadcrumb showing current location in the JSON tree.
• Raw mode toggle (switch between tree and text editor).

Security considerations

A jsonb_patch call with an incorrect path could corrupt data (e.g. overwriting the wrong nested key). The frontend should validate that the target path exists and show a preview of the resulting value before committing the patch.

Acceptance criteria

• validate_jsonb rejects malformed JSON with a position-aware error, accepts valid JSON
• jsonb_patch can add/remove/update a nested key without touching the rest of the document
• Frontend tree editor can toggle to raw text mode and back without data loss
• No regressions in existing Phase 1 parity tests

Tests

• test_insert_complex_jsonb — nested objects, arrays, mixed types
• test_update_jsonb_full_replace — overwrite entire value
• test_jsonb_patch_add_key — add key to existing object
• test_jsonb_patch_remove_key — remove key from object
• test_jsonb_patch_nested_update — modify deeply nested value
• test_invalid_jsonb_rejected — malformed JSON returns clear error

References

• Full spec: docs/planning/03-phase-2-issue-16.md (2.2)
• Priority: Sprint 2 — high demand, more complex (UI extension)
• Required for the Phase 2 stable-release gate (CP-5)