id: lib tests do not compile — idset.rs ChainExt initializer missing the note field #4044

Problem

On current main (verified at 2f8ab78), the id package's lib-test target does not compile, so no unit test in pkgs/id can run:

error[E0063]: missing field `note` in initializer of `chain::ChainExt`
   --> src/idset.rs:755:13

cargo test in pkgs/id fails at compile time with this single error (the lib itself builds clean). A test initializer in src/idset.rs constructs chain::ChainExt without the note field the struct now requires.

Evidence

• Reproduced 2026-11-01 by the queue worker (task 5050) on a clean checkout: cargo test server_config in pkgs/id fails with the error above.
• Proven pre-existing: with an unrelated change stashed (clean tree at origin/main 2f8ab78), cargo test server_config --no-run fails identically.
• Impact already felt: task 5050 (issue id(server_config): a blank or whitespace-padded key passes parse — a blank user key fails only mid-provisioning after earlier users are already created, and a padded key silently diverges from the account name it creates #1824) had to verify its new server_config parse tests through a temporary public-API integration harness instead of the crate's own unit-test target.

Acceptance

• cargo test in pkgs/id compiles the lib-test target again.
• The src/idset.rs ChainExt initializer supplies note with the semantics the surrounding test intends (not a placeholder that weakens the assertion).
• Full cargo test -p id (from pkgs/id) run recorded on this issue or the fixing PR.