release(7.15.0): RC19 audited firmware candidate

[BitHighlander]

Summary

This is the consolidated KeepKey firmware 7.15.0 candidate represented by the signed annotated tag v7.15.0-rc19.

• Ships Zcash Orchard in the regular firmware; the only alternate build is bitcoin-only.
• Adds the reviewed clear-signing, chain, BIP-85, recovery, and signing-policy work from the earlier 7.15 series.
• Includes the RC security remediation: constant-time RedPallas signing, host/ARM leakage gates, emulator CSPRNG handling, retirement of unauthenticated signer persistence, immutable release inputs, and usable Zcash signing progress.

Review shape

This single PR supersedes the closed #444–#448 stack and incorporates the later fork review, including BitHighlander#319 and #320. The history has been rebuilt as 12 ordered review units; snapshot commits and the temporary add/remove vendoring churn are gone.

The final source tree is identical to the RC19 reference tree f06cd8e87c71d96ad0c50f990e8cb5c7669f0772. The diff is 168 files, +21,569/−1,888; 7,273 added lines are test code. trezor-crypto is not vendored into this repository—it is pinned to the reviewed merge from keepkey/trezor-firmware#4 (62230ee620fa9ea2bdd2c8067be7fde3f9362248).

Validation

• Exact candidate CI: https://github.com/BitHighlander/keepkey-firmware/actions/runs/30220773721, fully green across regular and bitcoin-only ARM/emulator builds, unit/integration tests, crypto sanitizers, Valgrind taint checks, static analysis, formatting, secrets, and submodule policy.
• RC19 merge CI: https://github.com/BitHighlander/keepkey-firmware/actions/runs/30221786081.
• RC19 release workflow: https://github.com/BitHighlander/keepkey-firmware/actions/runs/30222630978, green; created an unsigned draft prerelease with regular and bitcoin-only artifacts, hash manifests, and pinned provenance.
• Clean-history branch CI: https://github.com/BitHighlander/keepkey-firmware/actions/runs/30221846030.
• Hardware-tested on the regular build: transparent to Orchard shield, Orchard to transparent deshield, and Orchard to Orchard private send, including multi-action signing and progress UI.
• RC19 regular firmware SHA-256: full file 22681eb2de6ad4c404bc2cf47da253dc36feb511a3f3af7d5f51e5be0fa4fa6e; device payload 651e6f53f11dcddf3e890250d4b81093eabfd73a948aea68125e6e6d2bc4ff6a.
• RC19 bitcoin-only firmware SHA-256: full file 8c64b7001a0751fc0ad93b02d369bbc7502fe8cc804e88e80f9113e6bfafeb5f; device payload 835d99f08fe128268cc50fdf68450e1c2576aa3437cba49fe003f96f6fa0d29f.

Merge gates

• Merge feat(protocol): 7.15 release additions — hive signing (1614-1617), clearsign identity icons, thorchain denom, ripple memo, zcash device-protocol#112 and test(7.15): consolidated Python harness, bindings, and device coverage python-keepkey#197, repin their canonical merge commits, and rerun exact-head CI.
• Complete upstream human review. RC artifacts remain unsigned draft prereleases; production publishing still requires the normal 3-of-5 signing and device-upgrade checklist.

[BitHighlander]

Closing this consolidated candidate. A 168-file, +21,569/−1,888 single PR is not reviewable in practice — it sat 10 days with green CI and no review, and its 12 internal units were lineage bundles (largest 6,436 lines) rather than feature slices.

The 7.15 content is being restaged from scratch as a stack of feature-sized review branches against BitHighlander/keepkey-firmware develop, which is now reset to this repository's develop tip (1af2ffe) so each branch is directly upstreamable. Every branch will carry its own CI run and Gate-3 evidence; a new RC will be cut from the restacked develop, and replacement upstream PRs will be opened per feature area.

Nothing is lost: the exact content of this candidate is preserved at tag preserve/alpha-2026-08-05 (f1f99a5) plus release/7.15.0-rc19-upstream. #449 stays independent.