feat(email): add GPG/PGP email signing and verification (#13)

Author: mqasimca

CLAUDE.md

@@ -64,6 +64,7 @@ make ci        # Runs: fmt → vet → lint → test-unit → test-race → secu
 - **CLI Framework**: Cobra
 - **API**: Nylas v3 ONLY (never use v1/v2)
 - **Timezone Support**: Offline utilities + calendar integration ✅
+- **Email Signing**: GPG/PGP email signing (RFC 3156 PGP/MIME) ✅
 - **Credential Storage**: System keyring (see below)
 - **Web UI**: Air - browser-based interface (localhost:7365)
 
@@ -123,10 +124,12 @@ Credentials from `nylas auth config` are stored in the system keyring under serv
 
 **Quick lookup:** CLI helpers in `internal/cli/common/`, HTTP in `client.go`, Air at `internal/air/`
 
-**New packages (2024):**
+**New packages (2024-2026):**
 - `internal/ports/output.go` - OutputWriter interface for pluggable formatting
 - `internal/adapters/output/` - Table, JSON, YAML, Quiet output adapters
 - `internal/httputil/` - HTTP response helpers (WriteJSON, LimitedBody, DecodeJSON)
+- `internal/adapters/gpg/` - GPG/PGP email signing service (2026)
+- `internal/adapters/mime/` - RFC 3156 PGP/MIME message builder (2026)
 
 **Full inventory:** `docs/ARCHITECTURE.md`
 

docs/COMMANDS.md

@@ -115,6 +115,8 @@ nylas email read <message-id>                                  # Read email
 nylas email read <message-id> --raw                            # Show raw body without HTML
 nylas email read <message-id> --mime                           # Show raw RFC822/MIME format
 nylas email send --to EMAIL --subject SUBJECT --body BODY      # Send email
+nylas email send --to EMAIL --subject SUBJECT --body BODY --sign  # Send GPG-signed email
+nylas email send --list-gpg-keys                               # List available GPG signing keys
 nylas email search --query "QUERY"                             # Search emails
 nylas email delete <message-id>                                # Delete email
 nylas email mark read <message-id>                             # Mark as read
@@ -136,7 +138,7 @@ nylas email ai analyze --provider claude  # Use specific AI provider
 nylas email smart-compose --prompt "..."  # AI-powered email generation
 ```
 
-**Details:** `docs/commands/email.md`, `docs/commands/ai.md`
+**Details:** `docs/commands/email.md`, `docs/commands/email-signing.md`, `docs/commands/ai.md`
 
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