Hydrate notes at transport boundaries before rewrites

[svarlamov]

Summary

• hydrate authorship notes after successful fetch/pull transport, before non-fast-forward rewrite handling
• fetch Git notes once from the selected remote instead of speculatively fetching all remotes from local rewrite destinations
• warm the HTTP cache from immutable trace2-derived incoming revision OIDs with one bounded rev-list and batched API reads
• defer transport-sync errors until rewrite and working-log side effects finish, then preserve the existing error reporting contract
• restore the authoritative force-pushed target regression and add the literal User A restack / User B extra-work rebase E2E
• cover the same ordering guarantee with the HTTP notes backend
• keep standalone cherry-pick target-note merging local, since no transport occurred to authorize a network fetch

Test plan

• task fmt
• task lint
• task test (full suite)
• task test TEST_FILTER=notes_sync_
• task test TEST_FILTER=does_not_fetch_notes_for_fresh
• task test TEST_FILTER=pull_rebase_force_pushed_target_preserves_remote_authorship_note
• task test TEST_FILTER=pull_rebase_after_collaborator_restack_preserves_both_users_notes
• task test TEST_FILTER=cherry_pick_merges_existing_authoritative_target_note

Stack

2 of 2. Depends on #2038.

[svarlamov]

• Hydrate notes at transport boundaries before rewrites #2039 👈 (View in Graphite)
• Stop fetching notes for fresh rewrite targets #2038
• main

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.