Backport the final merged preference-crypto fix (#8442) onto
`mobile-v0.25` for 0.25.1 RC3, preserving RC2's emoji and DM-sort fixes
(#8501).
Reconnects reuse identity/community-scoped preference crypto instead of
repeatedly deriving the same keys. The backport also includes the
reviewed signing-key normalization and identity-export corrections from
the final main revision. It is a clean cherry-pick with an identical
patch ID; no other main changes are included. No overlapping open
stable-backport PR was found.
### Validation
- All 47 focused stable-branch crypto, NIP-42 authentication, and
pairing tests pass, including padded-key normalization and
identity-export regressions.
- Full mobile pre-push checks and full repository `just ci` pass. Codex
review completed with no findings.
- The local branch-skew hook assumes `main` and is excluded for this
stable-target backport. Required stable-branch CI and review remain
enforced.
- No new device capture or release-frame benchmark. Stable-target
security review is unavailable under the current main-only workflow
policy.
Signed-off-by: Tom Brow <tomb@block.xyz>
cc789b657a