app/vtselect/traces/tempo: return matched spans in /api/search instead of root span

[yusufcemalcelebi]

Problem

The Tempo-compatible /select/tempo/api/search endpoint populated spanSets[].spans[] with the trace root span (carrying a synthesized nestedSetParent=-1 and only service.name) instead of the spans that actually satisfied the TraceQL filter.

Grafana's Tempo datasource deep-links to spanSets[].spans[].spanID, so clicking a result row always focused the root span rather than the matched child span (real Tempo focuses the matched span). matched was also coupled to root-span presence, returning 0 when the root had not yet been ingested even though child spans matched.

Fix

Retain the spans that matched the filter and project them into the response:

• query: mark the matched spans within the existing all-spans fetch (query 2) via a | format if (<filter>) "1" as _vt_matched pipe — no extra storage query/round-trip. Non-matching spans are still returned (carrying no marker), since trace-level metadata (duration, per-service stats) is derived from all spans of the trace.
• summary: build per-trace matchedSpans with their real spanID, name, start/duration and the query-referenced attributes (mirroring Tempo — kind/status rendered as names, scope prefixes stripped; name emitted only when referenced). matched reports the true count regardless of root presence, capped by spss. Root span is used only for trace-level metadata.
• parser: expose Query.ReferencedFields() and KindCodeToName for the projection.
• response: emit a serviceStats block (per-service span/error counts) and drop the synthesized root span / nestedSetParent=-1.
• parse the spss (spansPerSpanSet) query param (default 3, clamped to [1, 1000]).

Out of scope (follow-ups): accepting kind enum names like kind=consumer on input, and the top-level metrics block.

Testing

• Unit test (tempo_test.go): decisive case (root present but non-matching -> matched child returned, not root; the unmarked root is not counted) and the root-absent case (count still correct).
• End-to-end against a local single-node build (OTLP ingest of a non-matching root + matching child span, then real /api/search calls):
  • q={ span.http.status_code = "500" } -> returns the child spanID with only the query-referenced attribute (http.status_code: "500"), matched: 1, no nestedSetParent, trace metadata from the root, and a populated serviceStats (service-b -> errorCount: 1).
  • q={} -> both spans marked, matched: 2.
• make fmt, make vet, go build ./..., and tempo + traceql package tests pass.

[cubic-dev-ai]

1 issue found across 14 files

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