Instrument upload-level multi-copy golden path success rate

[BigLep]

Done Criteria

1. We can answer: what proportion of uploads achieve full multi-copy success — i.e. all requested copies stored (UploadResult.complete === true), not just per-copy attempt success.
2. The metric schema is documented in documentation/events-and-metrics.md before implementation (same doc-first pattern as #363).
3. Dashboards can slice golden-path success by affordance, network, requestedCopies, and (optionally) upload size.

Why Important

#363 / #501 added per-copy metrics (uploadCopyStatus, uploadCopySize) that answer:

Of all copy attempts, what fraction succeeded?

That is useful for SP/step regressions, but it does not answer the ORR golden-path question:

Of uploads that requested N copies, what fraction got all N?

Per-copy metrics can be skewed by uploads that request only one copy, or by uploads that request many copies (each failed copy adds weight). See PR #501 review discussion.

User/Customer

Maintainers / FOC working group

Proposed direction (draft — refine in events-and-metrics.md)

Emit one metric per executeUpload call (upload-level, not copy-level), e.g.:

Metric	When emitted	Suggested tags
uploadComplete (counter)	Once when executeUpload returns	complete (true/false), requestedCopies, achievedCopies, network, affordance, optionally size bucket or paired gauge

Alternative from #363 discussion: a multicopy tag (true/false/unknown) on upload-level metrics so dashboards can filter to multicopy=true uploads only.

Relationship to existing metrics: keep uploadCopyStatus / uploadCopySize for per-SP/per-step diagnostics; add upload-level metric(s) for golden-path rate. They complement each other.

Notes

1. Blocked by / follows: #501 (telemetry plumbing, BetterStack ingestion, affordance tag).
2. Partially addresses done criterion 1 of #363; criterion 2 (step + SP failure visibility) is already covered by per-copy metrics in feat: instrument multi-copy upload outcomes #501.
3. Spec out event markers first (e.g. extend uploadResultReceived or add uploadGoldenPathResolved) so metrics stay tied to documented events.
4. Consider whether complete should mirror Synapse's definition exactly (copies.length >= requestedCopies) vs. a stricter Filecoin Pin interpretation.
5. Query recipe to document: sum(uploadComplete where complete=true) / sum(uploadComplete) filtered by multicopy=true and/or requestedCopies>=2.

[BigLep]

Triage comment from 2026 FOC Board Triage (Post GA): Russell: This is a nice to have IMO, but other instrumentation on payments setup, first upload (any success) is much more important
Steve: the reason to prioritize this is its our only view into "how often is GA 2 copy replication working by default in the wild".