Module stage 

Pipeline-level transform stages. A TransformStage wraps one of four shapes:

• TransformStage::Map holds an unchanged 1→1 RecordTransform.
• TransformStage::Filter is a predicate-based 1→0|1 stage (added in Task 4).
• TransformStage::Explode expands an array field into 1→0..N output records (added in Task 5).
• TransformStage::Custom is an Fn(Value) -> Vec<Value> closure escape hatch for library callers.

apply_stages is the per-record runner: it flat-maps stages left to right, so order matters (a Filter after an Explode filters children). The observability wrapper crate::observability::instrumented_apply_stages calls this per record and aggregates the page-level counters.

Structs

CompiledExplodetransform-explode

Pre-compiled explode: path parsed once, prefix resolved once.

CompiledFiltertransform-filter

Pre-compiled filter: path parsed once, value cloned once.

CompiledPath

Pre-parsed JSONPath. Bad syntax surfaces at compile_stage time, not per record. The implementation is a hand-rolled parser for the v1 subset (bare key, dot path, bracketed string key) — sufficient because we need to walk parent-container chains for explode mutation, which the jsonpath_rust::query() API doesn’t expose.

ExplodeSpectransform-explode

Spec for TransformStage::Explode. Fans one record out into N records based on the array at path. Compiled into a CompiledExplode at pipeline-build time; per-record work is one path resolve + N clones + N merges.

FilterSpectransform-filter

Predicate spec for TransformStage::Filter. Compiled into a CompiledFilter at pipeline-build time; per-record work is a single path resolve + comparison.

Enums

CompiledStage

Pre-compiled stage. Per-record work is just lookup + comparison + flat-map.

FilterOptransform-filter

Comparison operator for FilterSpec.

OnMissingtransform-explode

Behaviour when an ExplodeSpec’s path doesn’t yield a non-empty array. The default is Passthrough because silently dropping records is the worst failure mode for ETL pipelines — surfacing the record unchanged lets downstream stages decide.

PathSegment

TransformStage

One stage in a transform pipeline.

Functions

apply_stages

Per-record stage runner. Returns 0..N output records. Pure; no metrics.

compile_stage

Compile a TransformStage into its CompiledStage form.