feat(gemini-web): Add conversation affinity selector

internal/provider/gemini-web/conversation/hash.go

@@ -0,0 +1,74 @@
+package conversation
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"strings"
+)
+
+// Message represents a minimal role-text pair used for hashing and comparison.
+type Message struct {
+	Role string `json:"role"`
+	Text string `json:"text"`
+}
+
+// StoredMessage mirrors the persisted conversation message structure.
+type StoredMessage struct {
+	Role    string `json:"role"`
+	Content string `json:"content"`
+	Name    string `json:"name,omitempty"`
+}
+
+// Sha256Hex computes SHA-256 hex digest for the specified string.
+func Sha256Hex(s string) string {
+	sum := sha256.Sum256([]byte(s))
+	return hex.EncodeToString(sum[:])
+}
+
+// ToStoredMessages converts in-memory messages into the persisted representation.
+func ToStoredMessages(msgs []Message) []StoredMessage {
+	out := make([]StoredMessage, 0, len(msgs))
+	for _, m := range msgs {
+		out = append(out, StoredMessage{Role: m.Role, Content: m.Text})
+	}
+	return out
+}
+
+// StoredToMessages converts stored messages back into the in-memory representation.
+func StoredToMessages(msgs []StoredMessage) []Message {
+	out := make([]Message, 0, len(msgs))
+	for _, m := range msgs {
+		out = append(out, Message{Role: m.Role, Text: m.Content})
+	}
+	return out
+}
+
+// hashMessage normalizes message data and returns a stable digest.
+func hashMessage(m StoredMessage) string {
+	s := fmt.Sprintf(`{"content":%q,"role":%q}`, m.Content, strings.ToLower(m.Role))
+	return Sha256Hex(s)
+}
+
+// HashConversationWithPrefix computes a conversation hash using the provided prefix (client identifier) and model.
+func HashConversationWithPrefix(prefix, model string, msgs []StoredMessage) string {
+	var b strings.Builder
+	b.WriteString(strings.ToLower(strings.TrimSpace(prefix)))
+	b.WriteString("|")
+	b.WriteString(strings.ToLower(strings.TrimSpace(model)))
+	for _, m := range msgs {
+		b.WriteString("|")
+		b.WriteString(hashMessage(m))
+	}
+	return Sha256Hex(b.String())
+}
+
+// HashConversationForAccount keeps compatibility with the per-account hash previously used.
+func HashConversationForAccount(clientID, model string, msgs []StoredMessage) string {
+	return HashConversationWithPrefix(clientID, model, msgs)
+}
+
+// HashConversationGlobal produces a hash suitable for cross-account lookups.
+func HashConversationGlobal(model string, msgs []StoredMessage) string {
+	return HashConversationWithPrefix("global", model, msgs)
+}