fix: account for cancelled queued backfill batches

[ke7haav]

Summary

Fixes #721.

Pond can cancel queued task-group work without invoking the submitted closure. Those batches previously retained zero-value BackfillResult entries, making unattempted ledger ranges appear successful.

Changes

• Initialize every result with its real batch and an explicit not-started error.
• Preserve the Pond task-group cancellation cause on queued, unstarted results.
• Propagate the task-group wait error after running work and recompression drain.
• Keep clean signal shutdown behavior for live ingestion only.
• Add a deterministic concurrency-1 cancellation regression test.

Scope

This PR is focused on #721.

It does not change ordinary processed-batch failure handling tracked by #688 or oldest-ledger cursor publication tracked by #689.

Testing

• Focused regression and shutdown tests
• Focused race tests
• 100-run determinism check
• make fmt
• go vet ./...
• golangci-lint v2.1.2
• Broad database-free race suite
• Repository-wide compile checks

The complete database-backed suite could not run locally because PostgreSQL on 127.0.0.1:5432 rejected the repository’s passwordless test DSN.

[Copilot]

Pull request overview

Fixes cancellation accounting for queued backfill batches.

Changes:

• Marks unstarted batches explicitly and preserves cancellation errors.
• Propagates backfill task-group failures while retaining clean live-ingestion shutdowns.
• Adds cancellation regression coverage.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/services/ingest_test.go	Adapts backfill tests to the new error return.
internal/services/ingest_backfill.go	Records and propagates cancelled batch states.
internal/services/ingest_backfill_test.go	Tests queued cancellation behavior.
internal/ingest/ingest.go	Restricts clean cancellation exits to live ingestion.
internal/ingest/ingest_test.go	Tests mode-specific shutdown classification.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated no new comments.