Milestone 1: core services + Mox ingest + wired v0 API

- internal/mail: MailBackend interface (Send/Start/Capabilities) + NullBackend.
- internal/core: inbox/message/thread services over pgx; default-pod bootstrap.
- IngestRaw: real mox/message parse → body extraction (text/html walk) →
  quote-stripping (extracted_text) → reference-based threading → store, all in
  one tx; emits message.received event; populates FTS tsvector.
- core implements mail.InboundSink (Deliver) so any backend feeds the same path.
- internal/api: v0 routes wired live (was 501) — create/list/get inbox, ingest,
  list/get messages, list/get thread(+messages), send/reply (503 via NullBackend).
- cmd/openmail serve: builds core + NullBackend, ensures default pod.

Verified e2e vs Postgres 16: inbox create; ingest original+reply → same thread
via In-Reply-To/References; extracted_text strips quoted history; thread detail
ordered; FTS matches 'invoice'; events written; send → honest 503. vet clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/core/inbox.go

@@ -0,0 +1,72 @@
+package core
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"time"
+
+	"github.com/jackc/pgx/v5"
+)
+
+type Inbox struct {
+	ID          string          `json:"id"`
+	PodID       string          `json:"pod_id"`
+	Address     string          `json:"address"`
+	DisplayName *string         `json:"display_name,omitempty"`
+	Metadata    json.RawMessage `json:"metadata,omitempty"`
+	CreatedAt   time.Time       `json:"created_at"`
+	UpdatedAt   time.Time       `json:"updated_at"`
+}
+
+const inboxCols = `id::text, pod_id::text, address, display_name, metadata, created_at, updated_at`
+
+func scanInbox(row pgx.Row) (Inbox, error) {
+	var ib Inbox
+	err := row.Scan(&ib.ID, &ib.PodID, &ib.Address, &ib.DisplayName, &ib.Metadata, &ib.CreatedAt, &ib.UpdatedAt)
+	return ib, err
+}
+
+// CreateInbox provisions a new agent-owned address within a pod.
+func (s *Service) CreateInbox(ctx context.Context, podID, address string, displayName *string) (Inbox, error) {
+	row := s.pool.QueryRow(ctx,
+		`INSERT INTO inboxes (pod_id, address, display_name)
+		 VALUES ($1, $2, $3)
+		 RETURNING `+inboxCols,
+		podID, address, nullStr(displayName))
+	return scanInbox(row)
+}
+
+func (s *Service) GetInbox(ctx context.Context, id string) (Inbox, error) {
+	ib, err := scanInbox(s.pool.QueryRow(ctx, `SELECT `+inboxCols+` FROM inboxes WHERE id = $1`, id))
+	if errors.Is(err, pgx.ErrNoRows) {
+		return Inbox{}, ErrNotFound
+	}
+	return ib, err
+}
+
+func (s *Service) GetInboxByAddress(ctx context.Context, address string) (Inbox, error) {
+	ib, err := scanInbox(s.pool.QueryRow(ctx, `SELECT `+inboxCols+` FROM inboxes WHERE address = $1`, address))
+	if errors.Is(err, pgx.ErrNoRows) {
+		return Inbox{}, ErrNotFound
+	}
+	return ib, err
+}
+
+func (s *Service) ListInboxes(ctx context.Context, podID string) ([]Inbox, error) {
+	rows, err := s.pool.Query(ctx,
+		`SELECT `+inboxCols+` FROM inboxes WHERE pod_id = $1 ORDER BY created_at DESC`, podID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []Inbox{}
+	for rows.Next() {
+		ib, err := scanInbox(rows)
+		if err != nil {
+			return nil, err
+		}
+		out = append(out, ib)
+	}
+	return out, rows.Err()
+}