copier: expose remaining copy time as a structured ETA

[aparajon]

Progress carried the copy ETA only inside the human-readable Summary string, so programmatic consumers (e.g. a control plane rendering per-table progress) had to parse log output to recover it — and couldn't tell "still measuring" from a real estimate.

This adds a structured ETA to the status API:

• status.ETA — a small value bundling State and Duration:
  • State: measuring (no copy rate yet, the TBD window), ready (Duration is valid), due (copy essentially complete, the DUE case), or none (not in row copy). Lets a consumer render "calculating…" during the initial window instead of a misleading 0.
  • Duration (time.Duration): the estimated remaining row-copy time, valid only when State == ready.
• status.Progress.ETA — the structured estimate.
• Copier.GetETAState() status.ETA — computes the state and duration in one read so they stay consistent.

A shared etaEstimate helper backs GetETA and GetETAState, removing the duplicated estimate math the buffered and unbuffered copiers each carried and keeping the string and structured forms in sync.

[morgo]

Do you want to merge in whats in #879 as well? These changes all serve the same purpose essentially.

[Copilot]

Pull request overview

This PR extends Spirit’s status/progress surface to expose row-copy ETA as a structured value (state + duration), instead of only embedding it in the human-readable Summary string. This enables programmatic consumers to distinguish “still measuring” vs “ready” vs “due” without parsing logs.

Changes:

• Introduces status.ETAState and status.ETA, and adds ETA status.ETA to status.Progress.
• Adds Copier.GetETAState() status.ETA and centralizes ETA math in a shared etaEstimate helper used by both buffered and unbuffered copiers.
• Updates migration progress reporting and tests to populate/assert the structured ETA, and adds unit coverage for the shared ETA estimator.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
pkg/status/progress.go	Adds structured ETA types (ETAState, ETA) and exposes ETA on status.Progress.
pkg/migration/runner.go	Populates the new structured Progress.ETA during CopyRows.
pkg/migration/binlog_test.go	Updates expected status.Progress values to include structured ETA state.
pkg/copier/copier.go	Adds GetETAState() to the Copier interface and introduces shared etaEstimate.
pkg/copier/buffered.go	Reuses etaEstimate for text ETA and adds GetETAState() implementation.
pkg/copier/unbuffered.go	Reuses etaEstimate for text ETA and adds GetETAState() implementation.
pkg/copier/copier_eta_test.go	Adds unit tests validating etaEstimate state/duration behavior.

Comments suppressed due to low confidence (1)

pkg/migration/runner.go:1026

• Progress() builds Summary using r.copier.GetETA() and then separately reads r.copier.GetETAState(); since both values are recomputed from mutable copy stats, the human Summary and structured ETA can disagree at boundaries (e.g. switching from measuring→ready/due). Consider adding a single copier snapshot API (e.g. GetETASnapshot() (string, status.ETA)) or otherwise deriving Summary’s ETA text from the structured ETA so both representations are guaranteed consistent. Also note move/datasync runners include ETA text in Summary but currently would leave Progress.ETA at its zero value, which may surprise programmatic consumers of the shared status.Progress type.

	}
	// Single-table mode: the checkpoint table name is derived from the table
	// name and same-table concurrency is already excluded by the metadata

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