Delta upgrades, patching, tag selection, and channel constraints

TRDIFF10 contains an 8-byte magic, three encoded int64 lengths, decompressed control tuples, and streamed zstd diff/extra blocks. Capture writer errors immediately, clean up completely, and verify final SHA-256 inline. Never read and write the same path across hops. Stable chains come from GitHub Releases; nightly uses GHCR tags. Reject dev versions, downgrades, and cross-channel chains; limits are depth 10 stable, 30 nightly, and ratio 0.6. On release/**, derive PREV_TAG from the prior branch series rather than the newest chronological stable release. Corrupt or oversized patches fall back to full download. Return readFile() buffers directly. Offline and nightly upgrades use the curl/GitHub standalone path.