fix(watch-only): make AddressCache::new fallible

[Sandipmandal25]

Description and Notes

Closes part of #463 and Competency Test for sob 2026 to be submitted along with proposal

AddressCache::new and AddressCacheInner::new previously panicked on database failures at startup.
This change makes both return Result<Self, WatchOnlyError<D::Error>>, allowing callers to handle errors instead of crashing.

changes

Replaced three production panics:

• database.load().expect("Could not load database")

  • propagated with ?

• database.save_stats(...).expect("Could not save stats")

  • propagated with ?

• self.database.get_stats().unwrap() (in maybe_derive_addresses)

  • let Ok(...) else { return }

Updated florestad.rs::load_wallet to propagate via
FlorestadError::CouldNotInitializeWallet.

verification

cargo test -p floresta-watch-only

• All 10 tests pass

• Includes new_returns_err_when_database_load_fails:

  • uses a FailingDatabase stub
  • load() returns Err
  • asserts AddressCache::new returns Err(WatchOnlyError::DatabaseError(_))
  • confirms no panic on startup path

checklist

• Followed contribution guidelines
• CI passed on fork
• Linked issue [Enhancement] Get rid of all unwrap, expect and panic outside test code #463

[jaoleal]

Closes part of #463 and Competency Test for sob 2026 to be submitted along with proposal

Just to be clear that was my mistake, a competency test ideally should not be a PR. Thats what i wrote on our discord channel: https://discord.com/channels/1185232004506198056/1488947854612365353/1489335077769838685

[jaoleal]

When i started reading the code here i noticed that this is partially addressed on #804 but i have the intuition that it will be discarded, AFAIK the approach there was already reviewed and validated, maybe you could steal the code there and implement it here ? (That is, the error handling for the watch only interface)

[Sandipmandal25]

When i started reading the code here i noticed that this is partially addressed on #804 but i have the intuition that it will be discarded, AFAIK the approach there was already reviewed and validated, maybe you could steal the code there and implement it here ? (That is, the error handling for the watch only interface)

hey @jaoleal when you say "it will be discarded" do you mean pr #804 ? also by "steal the code from #804" and should i just take the full lib.rs error handling changes from there?

[Sandipmandal25]

Closes part of #463 and Competency Test for sob 2026 to be submitted along with proposal

Just to be clear that was my mistake, a competency test ideally should not be a PR. Thats what i wrote on our discord channel: https://discord.com/channels/1185232004506198056/1488947854612365353/1489335077769838685

i missed this acknowledging my mistake.

[jaoleal]

hey @jaoleal when you say "it will be discarded" do you mean pr #804 ?

Yes, Im not certain what will be discarded but for sure the error handling for the AddressCache is desirable.

also by "steal the code from #804" and should i just take the full lib.rs error handling changes from there?

Yes, but only if you think its proper.

[Sandipmandal25]

hey @jaoleal when you say "it will be discarded" do you mean pr #804 ?

Yes, Im not certain what will be discarded but for sure the error handling for the AddressCache is desirable.

also by "steal the code from #804" and should i just take the full lib.rs error handling changes from there?

Yes, but only if you think its proper.

i willl expand this with the full lib.rs error handling changes.