BEGIN_COMMIT_OVERRIDE
chore: reverting accidental de-macroifycation of AuthRegistry (#20532)
docs: add delayedpublicmutable apiref, fix misc docs (#20512)
chore: rename simulateUtility -> executeUtility (#20572)
fix: enable contract debug logs in `aztec test` (#20580)
chore: merging next to merge-train/fairies (#20622)
END_COMMIT_OVERRIDE

…0512)

Cherry-pick of merge commit 1382d2b with conflicts.
Conflicts in:
- noir-projects/aztec-nr/aztec/src/state_vars/delayed_public_mutable.nr
- noir-projects/aztec-nr/aztec/src/state_vars/public_immutable.nr
- noir-projects/noir-contracts/contracts/app/auth_contract/src/main.nr
- noir-projects/noir-protocol-circuits/crates/types/src/traits.nr (modify/delete)

…1134, #21072, #21186, #21189, #21229, #21228, #21234, #21639) (#21745)

## Summary

Combined backport of 12 PRs to v4-next, cherry-picked in chronological
merge order:

1. #20512 — docs: add delayedpublicmutable apiref, fix misc docs
2. #20379 — feat: custom message handlers in Aztec.nr
3. #20831 — feat!: make unused msg disco fns private
4. #21024 — feat: add compile-time size check for events and error code
links
5. #21134 — chore: add warning on invalid recipients
6. #21072 — feat: add aztecaddress::is_valid
7. #21186 — chore: use returns `true` for boolean fns
8. #21189 — feat: add note hash and nullifier helper functions with
domain separation
9. #21229 — docs: small delayedpubmut update
10. #21228 — test: restore pubmut tests
11. #21234 — fix: claim contract & improve nullif docs
12. #21639 — feat!: split compute note hash and nullifier to reduce
hashing

Each PR is a separate commit (raw cherry-pick with conflicts left in),
followed by a single final commit that resolves all conflicts — making
it easy to review the conflict resolution independently.

## Conflict resolution (last commit)

- `delayed_public_mutable.nr` / `public_immutable.nr` — merged doc
comments from both sides
- `aztec.nr` macros — integrated custom message handler + split compute
functions
- `discovery/mod.nr` / `process_message.nr` — merged offchain inbox sync
+ custom handler dispatch + split compute
- `constants.nr` / `constants_tests.nr` — added new domain separators
- `Nargo.toml` — added custom_message_contract
- `netlify.toml` — merged error code redirects
- `auth_contract` — kept v4-next delay value
- `note_metadata.nr` — doc comment reformat
- `migration_notes.md` — merged migration notes from both sides
- Deleted `traits.nr` (v4-next uses `traits/` directory)


ClaudeBox log: https://claudebox.work/s/3145d1bd30977c20?run=1

---------

Co-authored-by: Nicolás Venturo <nicolas.venturo@gmail.com>