feat(ai): session harness contract — incomplete, run_id, confirm bind

Add docs/16 for session state machine, incomplete/resume, queue semantics,
and agent-loop/harness/MCP gap review. Wire RunOutcome on max-rounds,
run_id through audit, TrimMessages/Redact hooks, ConfirmBindHash on write
confirm path; session file skeleton without HTTP yet. No push.

server/internal/aitools/confirm_bind.go

@@ -0,0 +1,29 @@
+package aitools
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"strings"
+)
+
+// ConfirmBindHash 绑定 connection + 规范化语句；改语句则哈希变，须重确认。
+func ConfirmBindHash(connectionID, statement string) string {
+	connectionID = strings.TrimSpace(connectionID)
+	statement = strings.Join(strings.Fields(strings.TrimSpace(statement)), " ")
+	sum := sha256.Sum256([]byte(connectionID + "\n" + statement))
+	return hex.EncodeToString(sum[:])
+}
+
+// VerifyConfirmBind 校验客户端带回的 bind；空 bind 视为不合法（桌面路径必须带）。
+func VerifyConfirmBind(connectionID, statement, bind string) error {
+	bind = strings.TrimSpace(bind)
+	if bind == "" {
+		return fmt.Errorf("confirmBind required")
+	}
+	want := ConfirmBindHash(connectionID, statement)
+	if !strings.EqualFold(bind, want) {
+		return fmt.Errorf("confirmBind mismatch: statement or connection changed; re-confirm required")
+	}
+	return nil
+}