[BUG] dedup on a dotted object-hierarchy field throws "String cannot be cast to java.util.Map" (Calcite path)

[ahkcs]

Describe the bug

On the Calcite path (plugins.calcite.enabled=true), dedup on a dotted field that maps into an OpenSearch object hierarchy fails 100% of the time with a ClassCastException. The same field projected with | fields works, so the failure is specific to dedup (and any command that turns the field into a partition/group key).

To Reproduce

Index with an object hierarchy (e.g. OpenTelemetry logs):

PUT logs-otel/_mapping
{ "properties": { "resource": { "properties": { "attributes": { "properties":
  { "k8s": { "properties": { "namespace": { "properties": { "name": { "type": "keyword" }}}}}}}}}}

Query:

source=logs-otel
| dedup resource.attributes.k8s.namespace.name
| fields resource.attributes.k8s.namespace.name, severityText, body
| head 50

Result: java.sql.SQLException: exception while executing query: class java.lang.String cannot be cast to class java.util.Map.

Expected behavior

Dedup should deduplicate on the leaf value, exactly as | fields resource.attributes.k8s.namespace.name resolves it. No cast error.

Root cause

OpenSearchIndex.getFieldTypes() flattens the mapping and emits a column for every intermediate object node and leaf (OpenSearchDataType.traverseAndFlatten). Each object/STRUCT node becomes a Calcite MAP<VARCHAR,ANY> (OpenSearchTypeFactory ~L186-190). When the exact dotted leaf is not itself a distinct mapped column, QualifiedNameResolver matches the longest existing prefix (a MAP column) and wraps the remaining segments in an INTERNAL_ITEM/ITEM call — so the dedup key becomes a MAP-typed RexCall, not a scalar RexInputRef.

Two throw sites, both (Map<String,Object>) value on a scalar String:

• Agg-pushdown decode: ObjectContent.map() L81 (dedup w/o keepempty is rewritten to composite-agg + top_hits by DedupPushdownRule), reached via OpenSearchExprValueFactory.parse STRUCT branch + OpenSearchResponse.handleAggregationResponse.
• JDBC decode: OpenSearchTypeFactory.getExprValueByExprType STRUCT branch L347, via OpenSearchExecutionEngine.buildResultSet/processValue.

DedupPushdownRule's guards miss it: it only bails on bare-RexInputRef MAP/ARRAY, and the nested-path guard (Utils.resolveNestedPath) fires only for nested→ARRAY, never plain object→STRUCT. | fields avoids it by resolving the leaf scalar (ExprValueUtils.resolveRefPaths) without re-typing the parent object.

Plugins/paths affected

Calcite path only. V2/legacy is unaffected (no dedup pushdown; DedupeOperator resolves the leaf scalar in memory).

Proposed fix

1. QualifiedNameResolver: don't let a dedup/partition key silently become a MAP-typed ITEM when a scalar leaf is intended.
2. DedupPushdownRule: extend the guard to bail on MAP (STRUCT) / INTERNAL_ITEM keys, not just bare-RexInputRef MAP/ARRAY.
3. Defense-in-depth: guard the two Map casts to degrade a STRUCT-vs-scalar mismatch gracefully.
4. Add a CalcitePPLDedupIT case with an object hierarchy (+ CalciteNoPushdownIT). No current dedup test uses a dotted/object field.