[backport v4.32.0] feat: distinguish original-source identities

[ejgallego]

Summary

Backport #353 to v4.32.0.

Primary Review

• Primary review: feat: distinguish original-source identities #353
• Keep review comments on feat: distinguish original-source identities #353 unless this backport diverges materially.

Scope

• Backport the already-reviewed default-development change onto v4.32.0.
• Keep this PR limited to release-line-specific conflict resolution.
• Preserve one-to-one commit provenance with cherry-pick -x.

Backport Delta

• No intentional release-specific changes.
• If conflict resolution requires deviations from the default-development PR, describe them here.

[ejgallego]

Superseded by #442 after v4.34 became the default-development line and v4.32 retired. The primary #353 is now based on v4.34, with #442 as its required v4.33 backport.