feat: add deduplication engine with identity discovery

Content-hash based duplicate detection across accounts with soft-delete
merging. Three-signal identity discovery (From header, OAuth, config).
CLI commands: deduplicate (dry-run default, --apply, --undo) and
list-identities. All query paths exclude dedup-soft-deleted rows.

Author: jesserobbins

cmd/msgvault/cmd/account_scope.go

@@ -0,0 +1,77 @@
+package cmd
+
+import (
+	"fmt"
+
+	"github.com/wesm/msgvault/internal/store"
+)
+
+// AccountScope is the result of resolving a user-supplied --account
+// flag against the store.
+type AccountScope struct {
+	Input  string
+	Source *store.Source
+}
+
+// IsEmpty reports whether the scope resolved to nothing.
+func (s AccountScope) IsEmpty() bool {
+	return s.Source == nil
+}
+
+// SourceIDs returns the source IDs that this scope expands to.
+func (s AccountScope) SourceIDs() []int64 {
+	if s.Source != nil {
+		return []int64{s.Source.ID}
+	}
+	return nil
+}
+
+// DisplayName returns a human-readable label for the scope.
+func (s AccountScope) DisplayName() string {
+	if s.Source != nil {
+		return s.Source.Identifier
+	}
+	return ""
+}
+
+// ResolveAccount resolves a user-supplied --account string against
+// the store. Returns an empty scope if input is empty. Currently
+// looks up sources by identifier or display name; collection lookup
+// will be added when collections are implemented.
+func ResolveAccount(
+	st *store.Store, input string,
+) (AccountScope, error) {
+	scope := AccountScope{Input: input}
+	if input == "" {
+		return scope, nil
+	}
+
+	sources, err := st.GetSourcesByIdentifierOrDisplayName(input)
+	if err != nil {
+		return scope, fmt.Errorf(
+			"look up source for %q: %w", input, err,
+		)
+	}
+	if len(sources) == 0 {
+		return scope, fmt.Errorf(
+			"no account or source found for %q "+
+				"(try 'msgvault list-accounts')",
+			input,
+		)
+	}
+	if len(sources) > 1 {
+		names := make([]string, 0, len(sources))
+		for _, s := range sources {
+			names = append(names, fmt.Sprintf(
+				"%s (%s, id=%d)",
+				s.Identifier, s.SourceType, s.ID,
+			))
+		}
+		return scope, fmt.Errorf(
+			"ambiguous account %q matches multiple sources: %v",
+			input, names,
+		)
+	}
+	scope.Source = sources[0]
+	return scope, nil
+}

cmd/msgvault/cmd/build_cache.go

@@ -680,7 +680,7 @@ func setupSQLiteSource(duckDB *sql.DB, dbPath string) (cleanup func(), err error
 		query         string
 		typeOverrides string // DuckDB types parameter for read_csv_auto (empty = infer all)
 	}{
-		{"messages", "SELECT id, source_id, source_message_id, conversation_id, subject, snippet, sent_at, size_estimate, has_attachments, attachment_count, deleted_from_source_at, sender_id, message_type FROM messages WHERE sent_at IS NOT NULL",
+		{"messages", "SELECT id, source_id, source_message_id, conversation_id, subject, snippet, sent_at, size_estimate, has_attachments, attachment_count, deleted_from_source_at, sender_id, message_type FROM messages WHERE sent_at IS NOT NULL AND deleted_at IS NULL",
 			"types={'sent_at': 'TIMESTAMP', 'deleted_from_source_at': 'TIMESTAMP'}"},
 		{"message_recipients", "SELECT message_id, participant_id, recipient_type, display_name FROM message_recipients", ""},
 		{"message_labels", "SELECT message_id, label_id FROM message_labels", ""},