Phase 5: reply drafts — template/LLM draft, edit, SMTP send (AUD-71)

Implements Phase 5 of AGENTS.md §11 (FR-8, FR-15):

- Message detail pane (GET /partials/message) with body, recommended
  action, reply identity, template picker, editable draft, and history.
- internal/reply: OmniRoute (OpenAI-compatible) chat client and a
  template-based draft generator. All non-JEV models go through
  OmniRoute (§10).
- internal/mailops: SMTP send over smtp.gmail.com:587 with STARTTLS and
  the app password, forcing IPv4 (§9); FR-15 reply identity (send as the
  arrived-at X-Pm-Original-To address, else "Sam Rolfe"); threading via
  In-Reply-To/References; -check-smtp safe verification; and a
  [Gmail]/Sent Mail thread check.
- Migration v5 stores messages.message_id_header and drafts.sent_at;
  mailfetch parses Message-ID.
- Send is user-triggered only: CSRF + UI confirm + confirm=yes guard,
  no auto-send, duplicate-send refused. A sent reply files the original
  under Replied-to/<address> and logs every step (FR-13).
- Tests for reply, mailops SMTP/identity/thread check, store drafts and
  migration v5, and the server draft/edit/send guards.
- docs/phase5-replies.md, README, .env.example, docker-compose updated.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

internal/reply/draft.go

@@ -0,0 +1,160 @@
+// Draft generation for Phase 5 (FR-8): turn a message into a short reply using
+// a template and the OmniRoute gateway.
+package reply
+
+import (
+	"context"
+	"fmt"
+	"log/slog"
+	"strings"
+
+	"gitea.lab.audasmedia.com.au/sam/email_agent/internal/store"
+)
+
+// maxPromptBodyChars bounds how much of the original message is sent to the
+// model. Personal mail is usually short; this keeps the request cheap.
+const maxPromptBodyChars = 4000
+
+// maxDraftChars bounds the generated body before it is stored.
+const maxDraftChars = 8000
+
+// Request is one draft request.
+type Request struct {
+	// Message is the mail being replied to.
+	Message store.Message
+	// Category, Importance, and Action come from the latest classification.
+	Category   string
+	Importance string
+	Action     string
+	// TemplateID selects a built-in template. Empty picks one from Action.
+	TemplateID string
+	// Instruction is optional extra guidance Sam typed (for example "say the
+	// invoice is paid"). It is appended to the template instruction.
+	Instruction string
+	// Signer is the name used for the sign-off (default "Sam").
+	Signer string
+}
+
+// Generator produces reply drafts from an LLM client.
+type Generator struct {
+	client *Client
+	logger *slog.Logger
+}
+
+// NewGenerator builds a Generator.
+func NewGenerator(client *Client, logger *slog.Logger) *Generator {
+	if logger == nil {
+		logger = slog.New(slog.DiscardHandler)
+	}
+	return &Generator{client: client, logger: logger}
+}
+
+// Configured reports whether the LLM gateway is configured.
+func (g *Generator) Configured() bool { return g.client.Configured() }
+
+// Model returns the configured model alias.
+func (g *Generator) Model() string { return g.client.Model() }
+
+// Draft generates a reply body and returns it with the template that was used.
+func (g *Generator) Draft(ctx context.Context, req Request) (body, templateID string, err error) {
+	tmpl, ok := TemplateByID(req.TemplateID)
+	if !ok {
+		tmpl = TemplateForAction(req.Action)
+		if strings.TrimSpace(req.TemplateID) != "" {
+			g.logger.Warn("unknown reply template; using the action default",
+				"template", req.TemplateID, "used", tmpl.ID)
+		}
+	}
+
+	system, user := BuildPrompt(req, tmpl)
+	body, err = g.client.Complete(ctx, system, user)
+	if err != nil {
+		return "", "", err
+	}
+	body = cleanDraft(body, maxDraftChars)
+	if body == "" {
+		return "", "", fmt.Errorf("the model returned an empty draft")
+	}
+	return body, tmpl.ID, nil
+}
+
+// BuildPrompt builds the system and user prompts for a draft. It is exported so
+// the prompt shape can be tested without a live gateway.
+func BuildPrompt(req Request, tmpl Template) (system, user string) {
+	signer := strings.TrimSpace(req.Signer)
+	if signer == "" {
+		signer = "Sam"
+	}
+
+	system = strings.Join([]string{
+		"You write short, plain-text email replies on behalf of " + signer + ".",
+		"Return only the reply body: no subject line, no markdown, no placeholders, no quoted history.",
+		"Match the language of the incoming message.",
+		"Keep replies under 120 words and end with a sign-off of \"" + signer + "\".",
+		"If the incoming message is unclear, write a brief acknowledgement and ask one short question.",
+		"Never invent facts, prices, dates, or commitments. If a detail is missing, leave it out or ask about it.",
+	}, " ")
+
+	var b strings.Builder
+	b.WriteString("TEMPLATE: ")
+	b.WriteString(tmpl.Name)
+	b.WriteString("\n")
+	b.WriteString("INSTRUCTION: ")
+	b.WriteString(tmpl.Instruction)
+	b.WriteString("\n")
+	if extra := strings.TrimSpace(req.Instruction); extra != "" {
+		b.WriteString("SAM'S NOTE: ")
+		b.WriteString(extra)
+		b.WriteString("\n")
+	}
+	if cat := strings.TrimSpace(req.Category); cat != "" {
+		b.WriteString("CLASSIFICATION: category=")
+		b.WriteString(cat)
+		if imp := strings.TrimSpace(req.Importance); imp != "" {
+			b.WriteString(" importance=")
+			b.WriteString(imp)
+		}
+		if act := strings.TrimSpace(req.Action); act != "" {
+			b.WriteString(" suggested_action=")
+			b.WriteString(act)
+		}
+		b.WriteString("\n")
+	}
+	b.WriteString("\n--- ORIGINAL MESSAGE ---\n")
+	b.WriteString("From: ")
+	b.WriteString(strings.TrimSpace(req.Message.FromAddr))
+	b.WriteString("\n")
+	b.WriteString("Arrived at: ")
+	b.WriteString(strings.TrimSpace(req.Message.SourceAddress))
+	b.WriteString("\n")
+	b.WriteString("Subject: ")
+	b.WriteString(strings.TrimSpace(req.Message.Subject))
+	b.WriteString("\n\n")
+	b.WriteString(truncate(req.Message.BodyText, maxPromptBodyChars))
+	b.WriteString("\n--- END ---\n\nWrite the reply body now.")
+
+	return system, b.String()
+}
+
+// cleanDraft trims a generated draft. Some models wrap output in a code fence or
+// prefix it with a "Subject:" line even when told not to; strip those.
+func cleanDraft(s string, max int) string {
+	s = strings.TrimSpace(s)
+	s = strings.TrimPrefix(s, "```")
+	s = strings.TrimSuffix(s, "```")
+	s = strings.TrimSpace(s)
+	if strings.HasPrefix(strings.ToLower(s), "subject:") {
+		if i := strings.IndexByte(s, '\n'); i >= 0 {
+			s = strings.TrimSpace(s[i+1:])
+		}
+	}
+	return truncate(s, max)
+}
+
+func truncate(s string, max int) string {
+	s = strings.TrimSpace(s)
+	if len(s) <= max {
+		return s
+	}
+	return strings.TrimSpace(s[:max]) + "…"
+}