fix: align push diff with experimentalPushAll union semantics

[robrechtme]

Summary

• Recompute the deleted set leaf-by-leaf under experimentalPushAll + delete-absent so the diff matches what the multi-locale upload will actually do. detailedDiff collapses entirely-missing branches into a single undefined at the branch level, which lost the resolution needed to apply union semantics correctly.
• Skip deleted entries whose path is present in any other local locale — Loco's format=multi evaluates delete-absent against the union of locales, so union-protected entries won't actually be deleted.
• Tighten the allNoOp guard in push to only fail when the diff contains actionable add/update entries. Loco returns "Nothing updated" for successful delete-absent-only pushes too, which previously caused spurious push: no-op failures.
• Improve the no-op error message to point at loco-cli pull as a reconciliation step.
• Split the early-exit branches in push so the "delete-absent disabled" message no longer fires when the diff is empty.

Test plan

• pnpm test — 92 passing, including new coverage for branch-collapsed diffs, union-protected leaves, sibling-leaf retention, and deletion-only push success
• pnpm lint, pnpm format:check, pnpm build
• End-to-end against a live Loco project (en + nl locales):
  • Push 1 (add key only to en): asset created, source-fallback in nl
  • Push 2 (the bug-trigger second push): now Everything up to date! instead of push: no-op
  • Push 3 (real deletion): asset removed on Loco, exit 0 instead of misleading quota error

Fixes #56

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Project	Deployment	Actions	Updated (UTC)
loco-cli	Ready	Preview, Comment	May 12, 2026 9:21am