feat(opensearch): support reason-filtered, unscoped, paginated event queries

[LakshanSS]

Summary

Delivery Insights (DORA metrics, openchoreo/openchoreo#4248) needs the observer's aggregator to sweep controller-emitted delivery lifecycle events (DeploymentStarted/Succeeded/Failed/Recovered) across every namespace on a timer, via this module's events API. The shared adapter contract (observability-logs-adapter-api.yaml) has been extended with reasons, searchAfter/nextCursor, and an optional searchScope, but this module's QueryEvents handler still required a scope and had no reason filter or pagination beyond a single page — every aggregator call would 400.

This is scoped to the observability-logs-opensearch module only, to unblock verifying the Delivery Insights event pipeline end-to-end on local k3d. The same gap exists in aws-cloudwatch, gcp-cloudlogging, and openobserve (tracked as a separate follow-up issue for the full release).

• Allow searchScope to be omitted when reasons is set, running an unscoped sweep across all namespaces instead of 400ing.
• Add a reasons terms filter to the component, workflow, and new unscoped query builders.
• Add searchAfter/nextCursor pagination: sort now includes _seq_no as a tiebreaker (a numeric, always-doc-valued metadata field, unlike _id) so paging is stable when multiple events share a timestamp; nextCursor is set from the last hit's sort values when a page fills up.
• Regenerate models.gen.go/server.gen.go from the openchoreo laki-obs branch's updated observability-logs-adapter-api spec (not yet on main, since feat: add Delivery Insights (DORA metrics) store and read API to observer openchoreo#4248 hasn't merged) so the new request/response fields exist. The regen was done from the module's own last-generated spec snapshot patched with only the new fields, to keep the diff scoped — not a full resync against current upstream main.
• Fixed Client.Search not copying each hit's sort values through to the local Hit type, which the new cursor logic depends on.

Draft because it depends on openchoreo/openchoreo#4248 landing first (that PR is intentionally held open until the whole Delivery Insights feature — including this — is ready), and the generated code here will need re-syncing against main's spec once that merges.

Test plan

• go build ./...
• go vet ./...
• go test ./... (all packages pass; existing TestQueryEvents_*/TestBuildComponentEventsQuery_* tests updated for the SearchScope pointer change and new sort shape)
• New tests: unscoped reason-filtered sweep, missing-scope-without-reasons 400, invalid searchAfter cursor 400, nextCursor populated when a page fills up, cursor encode/decode round-trip, reasons terms filter on all three query builders
• End-to-end verification on local k3d against a real OpenSearch cluster (pending #4248 merge + INSIGHTS_EVENTS_SOURCE_ENABLED=true)

🤖 Generated with Claude Code

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Codecov Report

❌ Patch coverage is 78.28947% with 33 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
observability-logs-opensearch/internal/handlers.go	75.58%	17 Missing and 4 partials ⚠️
...ity-logs-opensearch/internal/opensearch/queries.go	83.33%	4 Missing and 4 partials ⚠️
...logs-opensearch/internal/opensearch/event_types.go	76.47%	2 Missing and 2 partials ⚠️

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[LakshanSS]

Heads-up on the ordering dependency: the spec side of this is now split out of openchoreo/openchoreo#4248 into its own small PR — openchoreo/openchoreo#4597 (48 lines, spec + regenerated client, no Delivery Insights behaviour).

Once #4597 lands on main, this module's codegen will pick up reasons, searchAfter/nextCursor and the optional searchScope, and this PR can come out of draft without waiting for the full #4248 review.

#4597 cites the enforcement in this PR — the 400 for an unscoped, reason-less query and TestQueryEvents_NoScope_NoReasons — as the answer to why the rule isn't expressed as a schema-level anyOf.